Redox Reactions
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Electrode Potentials
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Standard Electrode Potentials
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Standard Potentials and Gibbs Free Energy
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Standard Potentials and Equilibrium Constants
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Electrolytic Cells
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Electrolysis
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Corrosion
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[{"Name":"Redox Reactions","TopicPlaylistFirstVideoID":0,"Duration":null,"Videos":[{"Watched":false,"Name":"Reviewing Redox Reactions","Duration":"4m 34s","ChapterTopicVideoID":28656,"CourseChapterTopicPlaylistID":286838,"HasSubtitles":true,"ThumbnailPath":null,"UploadDate":null,"DurationForVideoObject":null,"Description":null,"MetaTitle":null,"MetaDescription":null,"Canonical":null,"VideoComments":[],"Subtitles":[{"Start":"00:00.000 ","End":"00:06.585","Text":"In early videos, we talked about redox reactions and how to balance them."},{"Start":"00:06.585 ","End":"00:11.940","Text":"In this video, we return to this topic in connection with electrochemistry."},{"Start":"00:11.940 ","End":"00:15.990","Text":"We\u0027re going to start our discussion of electrochemistry."},{"Start":"00:15.990 ","End":"00:20.610","Text":"Electrochemistry is based on oxidation-reduction reactions."},{"Start":"00:20.610 ","End":"00:23.295","Text":"What we call redox reactions."},{"Start":"00:23.295 ","End":"00:25.770","Text":"If the reaction is spontaneous,"},{"Start":"00:25.770 ","End":"00:30.840","Text":"we can use it to obtain electricity and if the reaction is non-spontaneous,"},{"Start":"00:30.840 ","End":"00:34.715","Text":"we can use electricity to force the reaction to occur."},{"Start":"00:34.715 ","End":"00:37.760","Text":"Here\u0027s an example of a redox reaction."},{"Start":"00:37.760 ","End":"00:42.680","Text":"Zinc reacts with copper sulfate in"},{"Start":"00:42.680 ","End":"00:48.065","Text":"solution to give us copper and zinc sulfate in solution."},{"Start":"00:48.065 ","End":"00:50.195","Text":"That\u0027s the full equation."},{"Start":"00:50.195 ","End":"00:54.485","Text":"We can write the net ionic equation as Zn"},{"Start":"00:54.485 ","End":"01:01.910","Text":"plus Cu^2+ giving us Cu plus Zn^2+."},{"Start":"01:01.910 ","End":"01:09.890","Text":"Here\u0027s a picture. Here\u0027s a zinc rod in a copper sulfate solution which is blue."},{"Start":"01:09.890 ","End":"01:16.340","Text":"These react, some copper is deposited on the zinc rod,"},{"Start":"01:16.340 ","End":"01:18.965","Text":"but because it oxidizes in air,"},{"Start":"01:18.965 ","End":"01:23.400","Text":"it\u0027s copper oxide, it\u0027s dark gray."},{"Start":"01:24.320 ","End":"01:28.759","Text":"This is copper oxide. Zinc sulfate solution is produced,"},{"Start":"01:28.759 ","End":"01:35.050","Text":"and zinc sulfate is colorless so we\u0027ve gone from a blue solution to a colorless solution."},{"Start":"01:35.050 ","End":"01:40.565","Text":"Now any redox reaction can be written as 2 half-reactions."},{"Start":"01:40.565 ","End":"01:45.980","Text":"Zinc goes to Zn^2+ plus 2 electrons."},{"Start":"01:45.980 ","End":"01:48.770","Text":"That\u0027s the oxidation step."},{"Start":"01:48.770 ","End":"01:58.285","Text":"There\u0027s an increase in the oxidation state of zinc from 0 to +2 and electrons are lost."},{"Start":"01:58.285 ","End":"02:00.760","Text":"Here are the 2 electrons that are lost and"},{"Start":"02:00.760 ","End":"02:05.230","Text":"the electrons appear on the right-hand side of the equation."},{"Start":"02:05.230 ","End":"02:09.995","Text":"On oxidation, the electrons appear on the right-hand side of the equation."},{"Start":"02:09.995 ","End":"02:12.995","Text":"Here\u0027s a reduction step."},{"Start":"02:12.995 ","End":"02:17.115","Text":"Cu^2+ gains 2 electrons to give"},{"Start":"02:17.115 ","End":"02:22.165","Text":"copper so there\u0027s a decrease in the oxidation state of copper."},{"Start":"02:22.165 ","End":"02:28.360","Text":"It goes from +2 to 0 and a gain of electrons,"},{"Start":"02:28.360 ","End":"02:30.670","Text":"electrons appear on the left-hand side of"},{"Start":"02:30.670 ","End":"02:34.480","Text":"the equations so on oxidation they\u0027re on the right-hand side,"},{"Start":"02:34.480 ","End":"02:38.550","Text":"in reduction they\u0027re on the left-hand side."},{"Start":"02:38.550 ","End":"02:43.960","Text":"Now that\u0027s a very simple example and we\u0027ll return to this several times."},{"Start":"02:43.960 ","End":"02:47.620","Text":"Let\u0027s look at 2 reactions with copper metal."},{"Start":"02:47.620 ","End":"02:53.080","Text":"Supposing we have copper metal in a solution of zinc nitrate,"},{"Start":"02:53.080 ","End":"02:55.730","Text":"there will be no reaction."},{"Start":"02:55.730 ","End":"03:00.120","Text":"You can see that this is the inverse reaction or"},{"Start":"03:00.120 ","End":"03:06.575","Text":"the reverse to what we had before when we had zinc reacting with Cu^2+."},{"Start":"03:06.575 ","End":"03:09.510","Text":"That\u0027s the reaction that occurs spontaneously,"},{"Start":"03:09.510 ","End":"03:11.230","Text":"this one does not."},{"Start":"03:11.230 ","End":"03:17.215","Text":"However, if we have copper in silver nitrate rather than zinc nitrate,"},{"Start":"03:17.215 ","End":"03:23.300","Text":"it will react and we get copper nitrate and silver and here\u0027s a picture."},{"Start":"03:23.300 ","End":"03:26.600","Text":"Silver nitrate is colorless."},{"Start":"03:26.600 ","End":"03:33.680","Text":"Here\u0027s our copper rod and it reacts to give a silver"},{"Start":"03:33.680 ","End":"03:41.675","Text":"deposited on the copper rod and a solution of copper nitrate, which is blue."},{"Start":"03:41.675 ","End":"03:50.345","Text":"Here we have copper is oxidized to Cu^2+ and Ag+ is reduced to silver."},{"Start":"03:50.345 ","End":"03:55.820","Text":"We can conclude from the fact that copper does not react with zinc nitrate,"},{"Start":"03:55.820 ","End":"03:58.565","Text":"but does react with silver nitrate,"},{"Start":"03:58.565 ","End":"04:05.650","Text":"we can conclude that Ag+ is more readily reduced by copper than Zn^2+."},{"Start":"04:05.650 ","End":"04:15.455","Text":"Now we can quantify this tendency of an ion to be reduced using electrode potentials."},{"Start":"04:15.455 ","End":"04:17.975","Text":"Using these electrode potentials,"},{"Start":"04:17.975 ","End":"04:21.665","Text":"we can explain why copper reacts with Ag+,"},{"Start":"04:21.665 ","End":"04:25.400","Text":"but doesn\u0027t react with Zn^2+ and this is"},{"Start":"04:25.400 ","End":"04:29.900","Text":"a subject we\u0027re going to develop in the next few videos."},{"Start":"04:29.900 ","End":"04:34.620","Text":"In this video, we reviewed redox reactions."}],"ID":30184},{"Watched":false,"Name":"Exercise 1 part a","Duration":"4m 25s","ChapterTopicVideoID":31549,"CourseChapterTopicPlaylistID":286838,"HasSubtitles":false,"ThumbnailPath":null,"UploadDate":null,"DurationForVideoObject":null,"Description":null,"MetaTitle":null,"MetaDescription":null,"Canonical":null,"VideoComments":[],"Subtitles":[],"ID":33685},{"Watched":false,"Name":"Exercise 1 part b","Duration":"5m 33s","ChapterTopicVideoID":31550,"CourseChapterTopicPlaylistID":286838,"HasSubtitles":false,"ThumbnailPath":null,"UploadDate":null,"DurationForVideoObject":null,"Description":null,"MetaTitle":null,"MetaDescription":null,"Canonical":null,"VideoComments":[],"Subtitles":[],"ID":33686},{"Watched":false,"Name":"Exercise 2 part a","Duration":"6m 33s","ChapterTopicVideoID":31551,"CourseChapterTopicPlaylistID":286838,"HasSubtitles":false,"ThumbnailPath":null,"UploadDate":null,"DurationForVideoObject":null,"Description":null,"MetaTitle":null,"MetaDescription":null,"Canonical":null,"VideoComments":[],"Subtitles":[],"ID":33687},{"Watched":false,"Name":"Exercise 2 part b","Duration":"7m 6s","ChapterTopicVideoID":31552,"CourseChapterTopicPlaylistID":286838,"HasSubtitles":false,"ThumbnailPath":null,"UploadDate":null,"DurationForVideoObject":null,"Description":null,"MetaTitle":null,"MetaDescription":null,"Canonical":null,"VideoComments":[],"Subtitles":[],"ID":33688}],"Thumbnail":null,"ID":286838},{"Name":"Electrode Potentials","TopicPlaylistFirstVideoID":0,"Duration":null,"Videos":[{"Watched":false,"Name":"Electrochemical Cells","Duration":"5m 33s","ChapterTopicVideoID":28658,"CourseChapterTopicPlaylistID":286839,"HasSubtitles":true,"ThumbnailPath":null,"UploadDate":null,"DurationForVideoObject":null,"Description":null,"MetaTitle":null,"MetaDescription":null,"Canonical":null,"VideoComments":[],"Subtitles":[{"Start":"00:00.000 ","End":"00:01.830","Text":"In the previous video,"},{"Start":"00:01.830 ","End":"00:05.520","Text":"we reviewed redox reactions and half-reactions."},{"Start":"00:05.520 ","End":"00:11.700","Text":"In this video, we\u0027ll discuss electrochemical half cells and full cells."},{"Start":"00:11.700 ","End":"00:15.520","Text":"Let\u0027s start with half- cells."},{"Start":"00:16.970 ","End":"00:22.670","Text":"An electrochemical half cell consists of a metal strip or rod,"},{"Start":"00:22.670 ","End":"00:24.410","Text":"which we call an electrode,"},{"Start":"00:24.410 ","End":"00:27.979","Text":"immersed in an aqueous solution of its ions."},{"Start":"00:27.979 ","End":"00:33.095","Text":"For example, copper metal immersed in a solution of copper sulfate."},{"Start":"00:33.095 ","End":"00:34.670","Text":"Copper sulfate, of course,"},{"Start":"00:34.670 ","End":"00:36.920","Text":"has CU 2+ ions."},{"Start":"00:36.920 ","End":"00:44.195","Text":"Here\u0027s the copper electrode inside a solution of copper sulfate."},{"Start":"00:44.195 ","End":"00:47.585","Text":"There\u0027s an equilibrium between copper metal,"},{"Start":"00:47.585 ","End":"00:50.595","Text":"and copper 2+, plus 2 electrons."},{"Start":"00:50.595 ","End":"00:52.125","Text":"Going from left to right,"},{"Start":"00:52.125 ","End":"00:55.820","Text":"copper goes to copper 2+, plus 2 electrons."},{"Start":"00:55.820 ","End":"00:59.480","Text":"That\u0027s oxidation process, which electrons are produced,"},{"Start":"00:59.480 ","End":"01:01.435","Text":"and going from right to left,"},{"Start":"01:01.435 ","End":"01:05.080","Text":"copper 2+, plus 2 electrons gives us copper,"},{"Start":"01:05.080 ","End":"01:07.865","Text":"that\u0027s left to right, right to left."},{"Start":"01:07.865 ","End":"01:11.165","Text":"The changes in the metal ions are very small."},{"Start":"01:11.165 ","End":"01:17.164","Text":"Some measurements are made on a combination of 2 half cells based on different metals."},{"Start":"01:17.164 ","End":"01:19.670","Text":"Let\u0027s look at an electrochemical cell."},{"Start":"01:19.670 ","End":"01:23.045","Text":"I\u0027ve called it a full cell to distinguish from a half cell,"},{"Start":"01:23.045 ","End":"01:26.015","Text":"but usually, it\u0027s just called electrochemical cell."},{"Start":"01:26.015 ","End":"01:29.395","Text":"Electrochemical cell consists of 2 half cells."},{"Start":"01:29.395 ","End":"01:32.060","Text":"Oxidation takes place in 1 half cell,"},{"Start":"01:32.060 ","End":"01:33.695","Text":"and reduction in the other."},{"Start":"01:33.695 ","End":"01:34.895","Text":"Now, a Galvanic,"},{"Start":"01:34.895 ","End":"01:36.250","Text":"or Voltaic cell,"},{"Start":"01:36.250 ","End":"01:39.980","Text":"generates electrical energy from a chemical reaction,"},{"Start":"01:39.980 ","End":"01:42.905","Text":"and has 2 names are there after Galvani,"},{"Start":"01:42.905 ","End":"01:47.060","Text":"who was infamous for his experiments on frog legs"},{"Start":"01:47.060 ","End":"01:51.650","Text":"or after Volta, most Italian scientists."},{"Start":"01:51.650 ","End":"01:53.705","Text":"Here\u0027s a famous example,"},{"Start":"01:53.705 ","End":"01:59.285","Text":"zinc plus copper sulfate to give us copper and zinc sulfate,"},{"Start":"01:59.285 ","End":"02:01.355","Text":"and that\u0027s called the Daniell cell."},{"Start":"02:01.355 ","End":"02:07.920","Text":"The net ionic equation is zinc metal plus copper 2+ in a solution,"},{"Start":"02:07.920 ","End":"02:11.090","Text":"to give us copper metal and zinc 2+,"},{"Start":"02:11.090 ","End":"02:13.474","Text":"and that\u0027s the net ionic equation."},{"Start":"02:13.474 ","End":"02:18.505","Text":"Now, the Daniell cell consists of 2 half cells,"},{"Start":"02:18.505 ","End":"02:20.460","Text":"zinc and zinc sulfate,"},{"Start":"02:20.460 ","End":"02:23.565","Text":"and copper and copper sulfate. Here\u0027s a picture."},{"Start":"02:23.565 ","End":"02:27.570","Text":"Here\u0027s a zinc electrode that\u0027s called"},{"Start":"02:27.570 ","End":"02:31.930","Text":"the anode and the copper electrode that\u0027s called the cathode."},{"Start":"02:31.930 ","End":"02:36.875","Text":"We have anode on the left-hand side and the cathode on the right-hand side,"},{"Start":"02:36.875 ","End":"02:42.535","Text":"and we usually label the anode as negative in this cell,"},{"Start":"02:42.535 ","End":"02:46.171","Text":"and the cathode is positive."},{"Start":"02:46.171 ","End":"02:49.715","Text":"In electrolytic cells, which we\u0027ll talk about later,"},{"Start":"02:49.715 ","End":"02:51.545","Text":"it\u0027s the opposite case."},{"Start":"02:51.545 ","End":"02:55.570","Text":"The anode is positive, cathode negative,"},{"Start":"02:55.570 ","End":"03:01.280","Text":"but still, oxidation takes place at the anode and reduction at the cathode."},{"Start":"03:01.280 ","End":"03:05.020","Text":"At the anode, which we said has a negative charge,"},{"Start":"03:05.020 ","End":"03:13.170","Text":"zinc metal goes to zinc 2+ in the solution and 2 electrons, that\u0027s oxidation."},{"Start":"03:13.170 ","End":"03:17.775","Text":"At the cathode, which we said had a positive charge, copper 2+,"},{"Start":"03:17.775 ","End":"03:21.645","Text":"takes 2 electrons to give us copper,"},{"Start":"03:21.645 ","End":"03:23.880","Text":"that\u0027s a reduction process."},{"Start":"03:23.880 ","End":"03:30.255","Text":"We have oxidation at the anode and reduction at the cathode."},{"Start":"03:30.255 ","End":"03:34.700","Text":"The electrons flow from the anode to the cathode here in"},{"Start":"03:34.700 ","End":"03:38.450","Text":"this wire via a voltmeter"},{"Start":"03:38.450 ","End":"03:42.055","Text":"that measures the difference in voltage between the half- cells,"},{"Start":"03:42.055 ","End":"03:45.740","Text":"and we\u0027ll call that E cell, the cell voltage,"},{"Start":"03:45.740 ","End":"03:47.735","Text":"or electromotive force,"},{"Start":"03:47.735 ","End":"03:51.460","Text":"EMF, we\u0027ll also call it the cell potential."},{"Start":"03:51.460 ","End":"03:53.280","Text":"Now, for this particular cell,"},{"Start":"03:53.280 ","End":"03:54.630","Text":"the Daniell cell,"},{"Start":"03:54.630 ","End":"03:57.410","Text":"E cell, and this is under standard conditions."},{"Start":"03:57.410 ","End":"04:00.110","Text":"The little 0 here means standard conditions,"},{"Start":"04:00.110 ","End":"04:03.430","Text":"is equal to 1.103 volts,"},{"Start":"04:03.430 ","End":"04:10.530","Text":"and the standard conditions are 1 molar zinc sulfate and 1 molar copper sulfate,"},{"Start":"04:10.530 ","End":"04:12.345","Text":"and we should remember,"},{"Start":"04:12.345 ","End":"04:16.565","Text":"that a volt is equal to joule divided by a coulomb."},{"Start":"04:16.565 ","End":"04:19.790","Text":"Now, in addition to the wire carrying the electrons,"},{"Start":"04:19.790 ","End":"04:22.505","Text":"we also have the salt bridge,"},{"Start":"04:22.505 ","End":"04:27.530","Text":"and a salt bridge contains a salt such as a gel containing KCl."},{"Start":"04:27.530 ","End":"04:29.990","Text":"It allows the migration of ions,"},{"Start":"04:29.990 ","End":"04:31.520","Text":"to complete the circuit."},{"Start":"04:31.520 ","End":"04:34.055","Text":"We have not just the flow of electrons,"},{"Start":"04:34.055 ","End":"04:39.755","Text":"but also flow of ions, electrons and ions."},{"Start":"04:39.755 ","End":"04:44.195","Text":"Here, we have KCl in the salt bridge."},{"Start":"04:44.195 ","End":"04:49.515","Text":"The Cl- ions migrate into the cell,"},{"Start":"04:49.515 ","End":"04:54.125","Text":"and they neutralize the excess zinc 2+ ions,"},{"Start":"04:54.125 ","End":"04:57.295","Text":"because here we have zinc going to zinc 2+,"},{"Start":"04:57.295 ","End":"05:03.395","Text":"and the chloride ions neutralize the zinc 2+."},{"Start":"05:03.395 ","End":"05:05.010","Text":"On the cathode side,"},{"Start":"05:05.010 ","End":"05:08.925","Text":"the K+ ions migrate here,"},{"Start":"05:08.925 ","End":"05:13.249","Text":"and they neutralize the excess sulfate ions."},{"Start":"05:13.249 ","End":"05:19.670","Text":"There are excess sulfate ions because copper 2+ is turning into copper,"},{"Start":"05:19.670 ","End":"05:22.865","Text":"leaving behind sulfate ions,"},{"Start":"05:22.865 ","End":"05:24.515","Text":"which needs to be neutralized,"},{"Start":"05:24.515 ","End":"05:26.450","Text":"and they are neutralized by the K+."},{"Start":"05:26.450 ","End":"05:33.150","Text":"In this video, we talked about electrochemical half-cells and full-cells."}],"ID":30185},{"Watched":false,"Name":"Cell Diagrams","Duration":"3m 54s","ChapterTopicVideoID":28657,"CourseChapterTopicPlaylistID":286839,"HasSubtitles":true,"ThumbnailPath":null,"UploadDate":null,"DurationForVideoObject":null,"Description":null,"MetaTitle":null,"MetaDescription":null,"Canonical":null,"VideoComments":[],"Subtitles":[{"Start":"00:00.000 ","End":"00:02.340","Text":"In the previous video,"},{"Start":"00:02.340 ","End":"00:04.890","Text":"we learned about electrochemical cells,"},{"Start":"00:04.890 ","End":"00:06.150","Text":"and in this video,"},{"Start":"00:06.150 ","End":"00:10.830","Text":"we\u0027ll learn how to describe a cell using a simple diagram."},{"Start":"00:10.830 ","End":"00:14.550","Text":"We\u0027re going to talk about cell diagrams."},{"Start":"00:14.550 ","End":"00:17.250","Text":"Now, we said in the previous video that we have"},{"Start":"00:17.250 ","End":"00:19.935","Text":"the anode half-cell on the left-hand side,"},{"Start":"00:19.935 ","End":"00:22.590","Text":"the cathode half-cell on the right-hand side."},{"Start":"00:22.590 ","End":"00:24.975","Text":"This is how we describe it."},{"Start":"00:24.975 ","End":"00:27.030","Text":"We have the metal electrode,"},{"Start":"00:27.030 ","End":"00:33.060","Text":"and then a vertical line to separate it from the metal ion solution,"},{"Start":"00:33.060 ","End":"00:37.804","Text":"that a double vertical line to separate the anode from the cathode."},{"Start":"00:37.804 ","End":"00:41.420","Text":"Then we have the metal line solution of the cathode,"},{"Start":"00:41.420 ","End":"00:43.295","Text":"a single line,"},{"Start":"00:43.295 ","End":"00:46.625","Text":"and the metal electrode, will see examples."},{"Start":"00:46.625 ","End":"00:50.870","Text":"Another possibility is that we don\u0027t have a metal electrode,"},{"Start":"00:50.870 ","End":"00:54.835","Text":"but an inert electrode like platinum."},{"Start":"00:54.835 ","End":"00:57.270","Text":"Then here\u0027s our double line,"},{"Start":"00:57.270 ","End":"01:02.950","Text":"we could have another redox couple and an inert electrode for the cathode."},{"Start":"01:02.950 ","End":"01:07.680","Text":"Here\u0027s the situation of 2 inert electrodes, 1 for the anode,"},{"Start":"01:07.680 ","End":"01:09.030","Text":"1 for the cathode,"},{"Start":"01:09.030 ","End":"01:10.890","Text":"and 2 redox couples,"},{"Start":"01:10.890 ","End":"01:13.195","Text":"1 for the anode and 1 for the cathode."},{"Start":"01:13.195 ","End":"01:15.605","Text":"We could have a combination of the 2,"},{"Start":"01:15.605 ","End":"01:17.390","Text":"we could have a metal electrode,"},{"Start":"01:17.390 ","End":"01:19.445","Text":"and the metal line solution,"},{"Start":"01:19.445 ","End":"01:24.875","Text":"in 1 side and a redox couple and an inert electrode and the other side."},{"Start":"01:24.875 ","End":"01:28.700","Text":"The anode is always on the left with its negative sign,"},{"Start":"01:28.700 ","End":"01:31.940","Text":"and the cathode on the right with its positive side."},{"Start":"01:31.940 ","End":"01:37.040","Text":"This vertical line is the boundary between the electrode and solution,"},{"Start":"01:37.040 ","End":"01:42.450","Text":"and the double vertical line indicates a salt bridge."},{"Start":"01:42.880 ","End":"01:45.530","Text":"Here\u0027s an example."},{"Start":"01:45.530 ","End":"01:47.990","Text":"This is the example we saw before,"},{"Start":"01:47.990 ","End":"01:50.050","Text":"the Daniell cell,"},{"Start":"01:50.050 ","End":"01:53.580","Text":"and zinc sulfate in the anode,"},{"Start":"01:53.580 ","End":"01:57.980","Text":"and copper and copper sulfate is a cathode."},{"Start":"01:57.980 ","End":"02:02.885","Text":"We indicate this as zinc solid."},{"Start":"02:02.885 ","End":"02:07.070","Text":"That\u0027s the rod, the zinc anode,"},{"Start":"02:07.070 ","End":"02:10.530","Text":"zinc 2 plus, it\u0027s in our solution,"},{"Start":"02:10.530 ","End":"02:13.460","Text":"and sometimes we can write the conditions."},{"Start":"02:13.460 ","End":"02:19.060","Text":"Here, it\u0027s an aqueous solution and has a concentration of 1 molar."},{"Start":"02:19.060 ","End":"02:22.850","Text":"The other side, copper 2 plus in solution,"},{"Start":"02:22.850 ","End":"02:28.235","Text":"copper sulfate, copper 2 plus in solution with a concentration of 1 molar."},{"Start":"02:28.235 ","End":"02:30.644","Text":"Here, we have the cathode,"},{"Start":"02:30.644 ","End":"02:35.120","Text":"copper rod as the cathode."},{"Start":"02:35.120 ","End":"02:36.815","Text":"That\u0027s how we write it."},{"Start":"02:36.815 ","End":"02:42.395","Text":"Left is the anode and right is the cathode."},{"Start":"02:42.395 ","End":"02:44.030","Text":"Here\u0027s another example."},{"Start":"02:44.030 ","End":"02:51.350","Text":"Suppose we have an inert electrode of platinum on the left-hand side and the anode,"},{"Start":"02:51.350 ","End":"02:56.660","Text":"a redox couple consisting of Fe^2+ with concentration is"},{"Start":"02:56.660 ","End":"03:03.965","Text":"0.10 molar and Fe^3+ with a concentration of 0.20 molar."},{"Start":"03:03.965 ","End":"03:10.940","Text":"This is called a redox couple Fe^2+ and Fe^3+."},{"Start":"03:10.940 ","End":"03:19.520","Text":"Another right-hand side silver rod in a silver solution at a concentration of 1 molar."},{"Start":"03:19.520 ","End":"03:23.000","Text":"Here is mixed situation,"},{"Start":"03:23.000 ","End":"03:28.355","Text":"1 side inert electrode and on the other side, a metal electrode."},{"Start":"03:28.355 ","End":"03:29.810","Text":"Now, the redox couple,"},{"Start":"03:29.810 ","End":"03:32.945","Text":"which here is Fe^2+, Fe^3+,"},{"Start":"03:32.945 ","End":"03:36.410","Text":"is always written with the reduced form to the left,"},{"Start":"03:36.410 ","End":"03:39.395","Text":"and the oxidized form of the right."},{"Start":"03:39.395 ","End":"03:43.700","Text":"Fe^2+ goes to Fe^3+, plus electron."},{"Start":"03:43.700 ","End":"03:49.880","Text":"This is the oxidized form on the right and the reduced form on the left."},{"Start":"03:49.880 ","End":"03:54.300","Text":"In this video, we learned about cell diagrams."}],"ID":30186},{"Watched":false,"Name":"Exercise 1 part a","Duration":"2m 43s","ChapterTopicVideoID":31554,"CourseChapterTopicPlaylistID":286839,"HasSubtitles":false,"ThumbnailPath":null,"UploadDate":null,"DurationForVideoObject":null,"Description":null,"MetaTitle":null,"MetaDescription":null,"Canonical":null,"VideoComments":[],"Subtitles":[],"ID":33689},{"Watched":false,"Name":"Exercise 1 part b","Duration":"5m 53s","ChapterTopicVideoID":31555,"CourseChapterTopicPlaylistID":286839,"HasSubtitles":false,"ThumbnailPath":null,"UploadDate":null,"DurationForVideoObject":null,"Description":null,"MetaTitle":null,"MetaDescription":null,"Canonical":null,"VideoComments":[],"Subtitles":[],"ID":33690},{"Watched":false,"Name":"Exercise 2 part a","Duration":"3m 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49s","ChapterTopicVideoID":28663,"CourseChapterTopicPlaylistID":286840,"HasSubtitles":true,"ThumbnailPath":"https://www.proprep.uk/Images/Videos_Thumbnails/28663.jpeg","UploadDate":"2022-03-13T10:20:01.2330000","DurationForVideoObject":"PT6M49S","Description":null,"MetaTitle":"Standard Electrode and Cell Potentials 1: Video + Workbook | Proprep","MetaDescription":"Electrochemistry - Standard Electrode Potentials. Watch the video made by an expert in the field. Download the workbook and maximize your learning.","Canonical":"https://www.proprep.uk/general-modules/all/general-chemistry/electrochemistry/standard-electrode-potentials/vid33693","VideoComments":[],"Subtitles":[{"Start":"00:00.000 ","End":"00:02.205","Text":"In the previous video,"},{"Start":"00:02.205 ","End":"00:04.320","Text":"we learned about cell diagrams."},{"Start":"00:04.320 ","End":"00:11.070","Text":"In this video, we\u0027ll learn about standard electrode potentials and cell potentials."},{"Start":"00:11.070 ","End":"00:16.530","Text":"We\u0027re going to talk first about cell voltage or cell potential."},{"Start":"00:16.530 ","End":"00:20.640","Text":"The cell voltage is a difference between the potentials of"},{"Start":"00:20.640 ","End":"00:26.180","Text":"the 2 half cells and it can be measured very accurately."},{"Start":"00:26.180 ","End":"00:31.520","Text":"However, the potential of an individual half cell which we call the electrode potential,"},{"Start":"00:31.520 ","End":"00:34.385","Text":"cannot be determined precisely."},{"Start":"00:34.385 ","End":"00:39.709","Text":"What we do is we compare the half cell whose potential we want to determine"},{"Start":"00:39.709 ","End":"00:45.850","Text":"with a reference half-cell whose potential is arbitrarily chosen to be 0."},{"Start":"00:45.850 ","End":"00:48.410","Text":"The standard hydrogen electrode,"},{"Start":"00:48.410 ","End":"00:50.690","Text":"which we can write as SHE,"},{"Start":"00:50.690 ","End":"00:54.450","Text":"is often chosen for this purpose."},{"Start":"00:55.300 ","End":"01:00.800","Text":"The standard hydrogen electrode is usually used as the reference."},{"Start":"01:00.800 ","End":"01:05.075","Text":"Here\u0027s a diagram of the standard hydrogen electrode."},{"Start":"01:05.075 ","End":"01:08.330","Text":"We have a platinum wire attached to"},{"Start":"01:08.330 ","End":"01:13.970","Text":"a platinum electrode and hydrogen gas is bubbled in through this tube."},{"Start":"01:13.970 ","End":"01:17.880","Text":"Now it\u0027s supposed to be an activity equal to"},{"Start":"01:17.880 ","End":"01:23.015","Text":"1 and that\u0027s approximately 1 atmosphere or 1 bar."},{"Start":"01:23.015 ","End":"01:26.810","Text":"The values of the standard hydrogen electrode don\u0027t vary"},{"Start":"01:26.810 ","End":"01:31.280","Text":"much from using 1 atmosphere or 1 bar."},{"Start":"01:31.280 ","End":"01:36.245","Text":"Inside the solution, we have H^plus ions."},{"Start":"01:36.245 ","End":"01:43.463","Text":"In this context, it\u0027s usually just written as H^plus rather than H_3O^plus."},{"Start":"01:43.463 ","End":"01:47.910","Text":"Here\u0027s hydrogen bubbles, these little white bubbles."},{"Start":"01:48.380 ","End":"01:59.980","Text":"The solution is also at Activity 1 and that\u0027s approximately 1 molar and it\u0027s HCl usually."},{"Start":"02:01.220 ","End":"02:06.000","Text":"Here we have written H^plus is 1 molar,"},{"Start":"02:06.000 ","End":"02:12.205","Text":"so we have an equilibrium that takes place in the surface of the platinum electrode."},{"Start":"02:12.205 ","End":"02:14.768","Text":"It\u0027s written as a reduction reaction."},{"Start":"02:14.768 ","End":"02:17.090","Text":"Here it is, 2H^plus,"},{"Start":"02:17.090 ","End":"02:20.315","Text":"plus 2 electrons to give H_2."},{"Start":"02:20.315 ","End":"02:25.710","Text":"We define E^0 of this equilibrium to be"},{"Start":"02:25.710 ","End":"02:31.970","Text":"0 so the electrode potential for the standard hydrogen electrode is 0."},{"Start":"02:31.970 ","End":"02:38.360","Text":"We write the standard hydrogen electrode as H^plus with a bar H_2,"},{"Start":"02:38.360 ","End":"02:40.745","Text":"that\u0027s because there are 2 different phases."},{"Start":"02:40.745 ","End":"02:44.420","Text":"Another bar, platinum, that\u0027s our electrode."},{"Start":"02:44.420 ","End":"02:50.485","Text":"If it\u0027s on the right-hand side of the cell or if it\u0027s in the left-hand side, platinum,"},{"Start":"02:50.485 ","End":"02:52.935","Text":"a bar H_2,"},{"Start":"02:52.935 ","End":"02:54.715","Text":"a bar H^plus,"},{"Start":"02:54.715 ","End":"02:57.665","Text":"if it\u0027s on the left-hand side of the cell."},{"Start":"02:57.665 ","End":"03:02.440","Text":"How are we going to determine the standard electrode potential?"},{"Start":"03:02.440 ","End":"03:07.205","Text":"By convention, the standard electrode potential E^0"},{"Start":"03:07.205 ","End":"03:12.235","Text":"measures the tendency for reduction process to occur at the electrode."},{"Start":"03:12.235 ","End":"03:14.180","Text":"It\u0027s very important to remember it\u0027s"},{"Start":"03:14.180 ","End":"03:19.130","Text":"a reduction process and it occurs under standard conditions."},{"Start":"03:19.130 ","End":"03:22.460","Text":"That\u0027s unit activity for the aqueous solution and that\u0027s"},{"Start":"03:22.460 ","End":"03:26.625","Text":"approximately 1 molar and a pressure of 1 bar."},{"Start":"03:26.625 ","End":"03:29.250","Text":"Often in tables you\u0027ll see they\u0027ve actually used"},{"Start":"03:29.250 ","End":"03:33.425","Text":"1 atmosphere for gases. Here\u0027s an example."},{"Start":"03:33.425 ","End":"03:38.225","Text":"Determine the standard electrode potential for Cu^2"},{"Start":"03:38.225 ","End":"03:45.040","Text":"plus 1 molar plus 2 electrons to give us copper solid."},{"Start":"03:45.040 ","End":"03:48.535","Text":"You see it\u0027s a reduction reaction."},{"Start":"03:48.535 ","End":"03:52.764","Text":"Just note that we write the standard electrode potential as E^0"},{"Start":"03:52.764 ","End":"03:56.935","Text":"with Cu^2 plus the left-hand side slash Cu."},{"Start":"03:56.935 ","End":"04:03.890","Text":"They ion to be reduced on the left-hand side under reduced ion or in this case,"},{"Start":"04:03.890 ","End":"04:08.010","Text":"it\u0027s a metal on the right-hand side exactly as"},{"Start":"04:08.010 ","End":"04:13.680","Text":"written in the reaction Cu^2 plus on the left-hand side Cu on the right-hand side."},{"Start":"04:13.680 ","End":"04:15.900","Text":"We put the Cu half cell,"},{"Start":"04:15.900 ","End":"04:17.010","Text":"the copper half cell,"},{"Start":"04:17.010 ","End":"04:19.230","Text":"on the right as the cathode,"},{"Start":"04:19.230 ","End":"04:23.560","Text":"and the standard hydrogen electrode on the left as the anode."},{"Start":"04:23.560 ","End":"04:26.820","Text":"Here it\u0027s written. Here\u0027s our anode,"},{"Start":"04:26.820 ","End":"04:29.880","Text":"that\u0027s our standard hydrogen electrode,"},{"Start":"04:29.880 ","End":"04:34.450","Text":"and here\u0027s our copper electrode on the cathode side."},{"Start":"04:34.450 ","End":"04:38.115","Text":"Here\u0027s the cathode reaction, Cu^2 plus,"},{"Start":"04:38.115 ","End":"04:41.720","Text":"plus 2 electrons to give us copper and the anode is"},{"Start":"04:41.720 ","End":"04:47.405","Text":"H_2 gas to give us 2H plus and 2 electrons."},{"Start":"04:47.405 ","End":"04:52.780","Text":"We can add these 2 together and then we get Cu^2 plus,"},{"Start":"04:52.780 ","End":"04:57.735","Text":"plus hydrogen, and the 2 electrons cancel."},{"Start":"04:57.735 ","End":"05:00.420","Text":"On the right-hand side we have the copper,"},{"Start":"05:00.420 ","End":"05:03.703","Text":"Cu, plus 2H^plus."},{"Start":"05:03.703 ","End":"05:07.635","Text":"Here\u0027s our overall reaction."},{"Start":"05:07.635 ","End":"05:14.220","Text":"We measure the cell potential and that\u0027s E^0 of the right-hand side,"},{"Start":"05:14.220 ","End":"05:18.090","Text":"the cathode, minus E^0 of the left-hand side, the anode."},{"Start":"05:18.090 ","End":"05:23.655","Text":"The difference of the two is 0.340 volt,"},{"Start":"05:23.655 ","End":"05:25.170","Text":"that\u0027s what we measure."},{"Start":"05:25.170 ","End":"05:29.735","Text":"Since the left-hand side, since this is 0,"},{"Start":"05:29.735 ","End":"05:40.100","Text":"we can work out that E^0 for the copper electrode is equal to 0.340 volt."},{"Start":"05:40.100 ","End":"05:41.930","Text":"In a future video we\u0027ll show that"},{"Start":"05:41.930 ","End":"05:48.905","Text":"the standard cell potential E^0 cell is proportional to minus Delta G^0 cell."},{"Start":"05:48.905 ","End":"05:51.035","Text":"That\u0027s the Gibbs free energy."},{"Start":"05:51.035 ","End":"05:57.035","Text":"That means that when E_cell is positive,"},{"Start":"05:57.035 ","End":"06:00.485","Text":"Delta G will be negative."},{"Start":"06:00.485 ","End":"06:05.660","Text":"That means that the reaction is spontaneous and will proceed left to right."},{"Start":"06:05.660 ","End":"06:09.320","Text":"When E cell is positive,"},{"Start":"06:09.320 ","End":"06:14.000","Text":"the reaction is spontaneous and will proceed left to right."},{"Start":"06:14.000 ","End":"06:17.565","Text":"That means that copper^2 plus,"},{"Start":"06:17.565 ","End":"06:19.410","Text":"that\u0027s the left to right reaction,"},{"Start":"06:19.410 ","End":"06:24.590","Text":"is more easily reduced than H plus that\u0027s going right to left."},{"Start":"06:24.590 ","End":"06:27.890","Text":"When E is 0 is positive,"},{"Start":"06:27.890 ","End":"06:33.800","Text":"the reaction tends to go from left to right and the coppe^2 plus or"},{"Start":"06:33.800 ","End":"06:40.520","Text":"whichever other metal ion we\u0027re talking about will be more easily reduced than H^plus."},{"Start":"06:40.520 ","End":"06:42.740","Text":"In this video, we discussed"},{"Start":"06:42.740 ","End":"06:48.930","Text":"standard electrode potentials and discuss another example in the next video."}],"ID":33693},{"Watched":false,"Name":"Standard Electrode and Cell Potentials 2","Duration":"7m 30s","ChapterTopicVideoID":28662,"CourseChapterTopicPlaylistID":286840,"HasSubtitles":true,"ThumbnailPath":null,"UploadDate":null,"DurationForVideoObject":null,"Description":null,"MetaTitle":null,"MetaDescription":null,"Canonical":null,"VideoComments":[],"Subtitles":[{"Start":"00:00.000 ","End":"00:01.740","Text":"In the previous video,"},{"Start":"00:01.740 ","End":"00:04.975","Text":"we learned about standard electrode and cell potentials."},{"Start":"00:04.975 ","End":"00:06.270","Text":"In this video,"},{"Start":"00:06.270 ","End":"00:08.940","Text":"we\u0027ll discuss more examples."},{"Start":"00:08.940 ","End":"00:13.260","Text":"Let\u0027s recall the definition of the standard electrode potential."},{"Start":"00:13.260 ","End":"00:16.560","Text":"By convention, that means international agreement."},{"Start":"00:16.560 ","End":"00:20.820","Text":"The standard electrode potential E^0 measures the tendency for"},{"Start":"00:20.820 ","End":"00:25.380","Text":"reduction process to occur at the electrode under standard conditions."},{"Start":"00:25.380 ","End":"00:27.165","Text":"What are standard conditions?"},{"Start":"00:27.165 ","End":"00:33.960","Text":"For aqueous solutions, 1 molar and for gases and pressure of 1 bar."},{"Start":"00:33.960 ","End":"00:38.880","Text":"In the previous video, we took the example of copper; copper 2 plus,"},{"Start":"00:38.880 ","End":"00:41.055","Text":"plus 2 electrons to give copper,"},{"Start":"00:41.055 ","End":"00:46.355","Text":"E^0 for that is plus 0.340 volts."},{"Start":"00:46.355 ","End":"00:48.395","Text":"Note that it\u0027s positive."},{"Start":"00:48.395 ","End":"00:51.500","Text":"Now, we\u0027re going to consider an example"},{"Start":"00:51.500 ","End":"00:55.175","Text":"where the electrode potential turns out to be negative."},{"Start":"00:55.175 ","End":"00:58.230","Text":"That\u0027s for zinc. Zinc 2 plus,"},{"Start":"00:58.230 ","End":"01:00.275","Text":"plus 2 electrons to give zinc."},{"Start":"01:00.275 ","End":"01:04.070","Text":"We want to find E^0 for zinc."},{"Start":"01:04.070 ","End":"01:07.939","Text":"We put the zinc half cylinder right as a cathode"},{"Start":"01:07.939 ","End":"01:12.335","Text":"and the standard hydrogen electrode on the left of the anode."},{"Start":"01:12.335 ","End":"01:14.719","Text":"Here\u0027s the cell diagram."},{"Start":"01:14.719 ","End":"01:19.490","Text":"On the left-hand side we have the standard hydrogen electrode,"},{"Start":"01:19.490 ","End":"01:22.960","Text":"and the right-hand side zinc."},{"Start":"01:22.960 ","End":"01:26.760","Text":"At the cathode, zinc 2 plus,"},{"Start":"01:26.760 ","End":"01:31.115","Text":"plus 2 electrons to give zinc is a reduction process."},{"Start":"01:31.115 ","End":"01:36.805","Text":"At the anode we have H_2 hydrogen gas 1 bar pressure,"},{"Start":"01:36.805 ","End":"01:41.040","Text":"going to 2 H plus aqueous solution at"},{"Start":"01:41.040 ","End":"01:46.630","Text":"1 molar plus 2 electrons and that\u0027s an oxidation process."},{"Start":"01:46.660 ","End":"01:51.775","Text":"Reduction at the cathode and oxidation at the end."},{"Start":"01:51.775 ","End":"01:55.830","Text":"Overall, that zinc 2 plus,"},{"Start":"01:55.830 ","End":"01:58.230","Text":"plus hydrogen to give"},{"Start":"01:58.230 ","End":"02:06.405","Text":"zinc metal plus 2 hydrogen plus and of course the 2 electrons cancels."},{"Start":"02:06.405 ","End":"02:09.080","Text":"Now when we measure the cell potential,"},{"Start":"02:09.080 ","End":"02:14.004","Text":"we get minus 0.763 volts."},{"Start":"02:14.004 ","End":"02:20.040","Text":"The cell potential is E^0 for the cathode minus E^0 for the anode."},{"Start":"02:20.040 ","End":"02:27.440","Text":"That\u0027s E^0 for zinc minus 0 because we have 0 for the standard hydrogen electrode."},{"Start":"02:27.440 ","End":"02:31.780","Text":"E^0 is equal to 0."},{"Start":"02:31.780 ","End":"02:40.885","Text":"That means the E cell is equal to E^0 for zinc because of the minus 0 here."},{"Start":"02:40.885 ","End":"02:48.134","Text":"We have E^0 for zinc equal to minus 0.763 volts."},{"Start":"02:48.134 ","End":"02:50.370","Text":"In contrast to copper,"},{"Start":"02:50.370 ","End":"02:53.430","Text":"now we have E^0 that\u0027s negative."},{"Start":"02:53.430 ","End":"02:58.640","Text":"Now, the negative sign means that Delta G^0 is positive,"},{"Start":"02:58.640 ","End":"03:01.765","Text":"and the reverse reaction is a spontaneous one."},{"Start":"03:01.765 ","End":"03:05.070","Text":"Right to left is spontaneous."},{"Start":"03:05.070 ","End":"03:11.690","Text":"That means that zinc 2 plus is less easily reduced than H plus."},{"Start":"03:11.690 ","End":"03:15.330","Text":"H plus is reduced to H_2."},{"Start":"03:15.350 ","End":"03:20.750","Text":"Now, let\u0027s write some rules based on"},{"Start":"03:20.750 ","End":"03:25.805","Text":"this observation and the observations in the previous video."},{"Start":"03:25.805 ","End":"03:30.775","Text":"Let\u0027s start off with standard electrode potential being positive."},{"Start":"03:30.775 ","End":"03:34.135","Text":"If the standard electrode potential is positive,"},{"Start":"03:34.135 ","End":"03:40.000","Text":"reduction of the metal ion occurs more easily than the reduction of H plus."},{"Start":"03:40.000 ","End":"03:42.535","Text":"That\u0027s what we found in the previous video."},{"Start":"03:42.535 ","End":"03:45.760","Text":"Now another way of saying the same thing is"},{"Start":"03:45.760 ","End":"03:48.730","Text":"that if the standard electrode potential is positive,"},{"Start":"03:48.730 ","End":"03:52.520","Text":"the metal cation is reduced by H_2."},{"Start":"03:52.520 ","End":"03:55.510","Text":"Here\u0027s our metal cation and CU^2 plus,"},{"Start":"03:55.510 ","End":"03:58.085","Text":"and it\u0027s reduced to copper."},{"Start":"03:58.085 ","End":"04:01.785","Text":"The reducing agent is H_2."},{"Start":"04:01.785 ","End":"04:05.409","Text":"Here we have, if the standard electrode potential is positive,"},{"Start":"04:05.409 ","End":"04:09.065","Text":"the metal cation is reduced by hydrogen."},{"Start":"04:09.065 ","End":"04:13.850","Text":"Now if the standard electrode potential is negative rather than positive,"},{"Start":"04:13.850 ","End":"04:20.110","Text":"reduction of the metal cation occurs less easily than reduction of H plus."},{"Start":"04:20.110 ","End":"04:22.975","Text":"That\u0027s what we found for zinc."},{"Start":"04:22.975 ","End":"04:28.340","Text":"Another way of saying this is that if the standard electrode potential is negative,"},{"Start":"04:28.340 ","End":"04:31.240","Text":"the metal reduces H plus."},{"Start":"04:31.240 ","End":"04:38.320","Text":"Here\u0027s our reaction, zinc 2 plus plus hydrogen to give zinc plus 2 H plus."},{"Start":"04:38.320 ","End":"04:42.230","Text":"Now we saw that it should go from right to left."},{"Start":"04:42.230 ","End":"04:45.515","Text":"The spontaneous direction is right to left."},{"Start":"04:45.515 ","End":"04:50.800","Text":"That means H plus is being reduced to H_2."},{"Start":"04:50.800 ","End":"04:54.995","Text":"The reducing agent is the metal zinc."},{"Start":"04:54.995 ","End":"04:57.830","Text":"The standard electrode potential is negative,"},{"Start":"04:57.830 ","End":"05:01.765","Text":"the metal reduces H plus."},{"Start":"05:01.765 ","End":"05:09.130","Text":"H plus is reduced to H_2 and zinc is a reducing agent."},{"Start":"05:09.130 ","End":"05:13.820","Text":"Now, let\u0027s say a few words about the reactions with acids."},{"Start":"05:13.820 ","End":"05:21.085","Text":"This last rule means that metals with negative standard electrode potentials like zinc,"},{"Start":"05:21.085 ","End":"05:26.775","Text":"react with acids such as HCl, HBr, and HI."},{"Start":"05:26.775 ","End":"05:29.370","Text":"Here\u0027s zinc reacting with H plus."},{"Start":"05:29.370 ","End":"05:32.765","Text":"We\u0027ll talk about more about that in the next video."},{"Start":"05:32.765 ","End":"05:35.440","Text":"Now here\u0027s some more examples."},{"Start":"05:35.440 ","End":"05:40.320","Text":"Fluorine is reduced to F"},{"Start":"05:40.320 ","End":"05:46.760","Text":"minus and E^0 for that is plus 2.866 volts."},{"Start":"05:46.760 ","End":"05:48.785","Text":"That\u0027s a very high number."},{"Start":"05:48.785 ","End":"05:53.023","Text":"That means fluorine is strongly reduced,"},{"Start":"05:53.023 ","End":"05:57.859","Text":"and that also means fluorine is a strong oxidizing agent."},{"Start":"05:57.859 ","End":"06:01.580","Text":"Now let\u0027s take silver, silver plus,"},{"Start":"06:01.580 ","End":"06:09.964","Text":"plus electron to gives silver and E^0 for this is plus 0.800 volts."},{"Start":"06:09.964 ","End":"06:13.790","Text":"That means that silver doesn\u0027t"},{"Start":"06:13.790 ","End":"06:17.735","Text":"react with acid because its electrode potential is positive."},{"Start":"06:17.735 ","End":"06:22.395","Text":"Another example, Fe^3 plus going to Fe^2 plus."},{"Start":"06:22.395 ","End":"06:28.200","Text":"Here E^0 is again positive plus 0.771 volts."},{"Start":"06:28.200 ","End":"06:31.265","Text":"That means it doesn\u0027t react with acid."},{"Start":"06:31.265 ","End":"06:36.665","Text":"Now if we take sodium in contrast to silver and iron,"},{"Start":"06:36.665 ","End":"06:40.445","Text":"sodium plus is reduced sodium,"},{"Start":"06:40.445 ","End":"06:46.295","Text":"that means that silver reacts with acid and indeed it reacts rather violently with acid,"},{"Start":"06:46.295 ","End":"06:50.470","Text":"and it even reacts with water as we\u0027ll see in a future video."},{"Start":"06:50.470 ","End":"06:52.775","Text":"Now if we take lithium,"},{"Start":"06:52.775 ","End":"06:55.400","Text":"lithium plus reduced to lithium,"},{"Start":"06:55.400 ","End":"07:01.240","Text":"E^0 for this is very negative, minus 3.05 volts."},{"Start":"07:01.240 ","End":"07:05.535","Text":"That means that lithium is strongly oxidize,"},{"Start":"07:05.535 ","End":"07:10.620","Text":"this spontaneous direction is the opposite direction this way,"},{"Start":"07:10.620 ","End":"07:14.115","Text":"and lithium is a strong reducing agent."},{"Start":"07:14.115 ","End":"07:17.795","Text":"We have a fluorine strong oxidizing agent,"},{"Start":"07:17.795 ","End":"07:20.405","Text":"and lithium strong reducing agent."},{"Start":"07:20.405 ","End":"07:24.700","Text":"We\u0027ll talk about other substances in future videos."},{"Start":"07:24.700 ","End":"07:30.660","Text":"In this video, we continued the discussion of standard electrode potentials."}],"ID":33694},{"Watched":false,"Name":"Electrochemical Series","Duration":"6m 30s","ChapterTopicVideoID":28664,"CourseChapterTopicPlaylistID":286840,"HasSubtitles":true,"ThumbnailPath":null,"UploadDate":null,"DurationForVideoObject":null,"Description":null,"MetaTitle":null,"MetaDescription":null,"Canonical":null,"VideoComments":[],"Subtitles":[{"Start":"00:00.000 ","End":"00:02.850","Text":"In the 2 previous videos,"},{"Start":"00:02.850 ","End":"00:06.690","Text":"we learned about standard electrode and cell potentials."},{"Start":"00:06.690 ","End":"00:10.870","Text":"We\u0027re going to talk about the electrochemical series."},{"Start":"00:11.360 ","End":"00:16.300","Text":"Now when the redox couples are ordered by their standard electrode potentials,"},{"Start":"00:16.300 ","End":"00:18.825","Text":"you\u0027ll see lists like this in many books."},{"Start":"00:18.825 ","End":"00:24.420","Text":"It\u0027s equivalent to a list of oxidizing and reducing agents ordered by their strengths."},{"Start":"00:24.420 ","End":"00:28.110","Text":"We have the positive standard electrode potentials"},{"Start":"00:28.110 ","End":"00:31.035","Text":"at the top and the negative ones at the bottom."},{"Start":"00:31.035 ","End":"00:35.384","Text":"In this context the list is called the electrochemical series."},{"Start":"00:35.384 ","End":"00:37.440","Text":"Here is 3 examples."},{"Start":"00:37.440 ","End":"00:39.075","Text":"At the top of the list,"},{"Start":"00:39.075 ","End":"00:41.505","Text":"fluorine_2 plus 2 electrons,"},{"Start":"00:41.505 ","End":"00:46.730","Text":"giving us 2 fluorine minus and that has the highest electrode potential,"},{"Start":"00:46.730 ","End":"00:49.400","Text":"the most positive electrode potential."},{"Start":"00:49.400 ","End":"00:55.475","Text":"Then we can say that fluorine is the strongest oxidizing agent."},{"Start":"00:55.475 ","End":"00:59.870","Text":"Now at the bottom we have lithium^+ plus electron to give us lithium and"},{"Start":"00:59.870 ","End":"01:04.685","Text":"that has the most negative electrode potential."},{"Start":"01:04.685 ","End":"01:10.100","Text":"We can see that the strongest reducing agent is lithium."},{"Start":"01:10.100 ","End":"01:14.375","Text":"The more positive the standard electrode potential,"},{"Start":"01:14.375 ","End":"01:16.205","Text":"that\u0027s going up the way,"},{"Start":"01:16.205 ","End":"01:20.990","Text":"the greater the strength of the oxidized form as an oxidizing agent."},{"Start":"01:20.990 ","End":"01:25.375","Text":"That\u0027s the top-left of the list here, fluorine_2."},{"Start":"01:25.375 ","End":"01:30.350","Text":"The more negative the standard electrode potential that\u0027s going down here,"},{"Start":"01:30.350 ","End":"01:34.430","Text":"the greater the strength of the reduced form as a reducing agent."},{"Start":"01:34.430 ","End":"01:37.715","Text":"That\u0027s the bottom right of the list here, lithium."},{"Start":"01:37.715 ","End":"01:41.240","Text":"The strongest oxidizing agent is fluorine_2,"},{"Start":"01:41.240 ","End":"01:44.000","Text":"and the strongest reducing agent is lithium."},{"Start":"01:44.000 ","End":"01:48.620","Text":"Let\u0027s solve 2 examples to test this assertion."},{"Start":"01:48.620 ","End":"01:54.410","Text":"The question is, E^0 for calcium is minus 2.868"},{"Start":"01:54.410 ","End":"01:59.913","Text":"volts and E^0 for lead is minus 0.125 volts,"},{"Start":"01:59.913 ","End":"02:02.520","Text":"which is a stronger reducing agent?"},{"Start":"02:02.520 ","End":"02:04.790","Text":"Calcium or lead?"},{"Start":"02:04.790 ","End":"02:07.895","Text":"Now the more negative is calcium,"},{"Start":"02:07.895 ","End":"02:13.520","Text":"so calcium is the most negative and the reduced form here is calcium metal,"},{"Start":"02:13.520 ","End":"02:16.565","Text":"the oxidized form is calcium^2+,"},{"Start":"02:16.565 ","End":"02:21.545","Text":"so Calcium should be the stronger reducing agent according to what we wrote before."},{"Start":"02:21.545 ","End":"02:24.295","Text":"Let\u0027s test this numerically."},{"Start":"02:24.295 ","End":"02:28.035","Text":"Here we\u0027re writing the electrode potential for calcium."},{"Start":"02:28.035 ","End":"02:35.450","Text":"Calcium ^2+ plus 2 electrons to give calcium and E^0 is minus 2.868 volts."},{"Start":"02:35.450 ","End":"02:40.390","Text":"Now if we turn the equation around so the E^0 is now positive,"},{"Start":"02:40.390 ","End":"02:46.300","Text":"we get calcium reacting to give us calcium^2+ plus 2 electrons."},{"Start":"02:46.300 ","End":"02:48.555","Text":"Now it\u0027s oxidation."},{"Start":"02:48.555 ","End":"02:53.285","Text":"That was reduction and we\u0027ve turned it around to give us oxidation."},{"Start":"02:53.285 ","End":"02:55.415","Text":"Here\u0027s the equation for lead,"},{"Start":"02:55.415 ","End":"02:59.480","Text":"lead^2+ plus 2 electrons to give us lead and E^0 is"},{"Start":"02:59.480 ","End":"03:05.135","Text":"minus 0.125 volts and this of course its reduction."},{"Start":"03:05.135 ","End":"03:10.055","Text":"Now, if we add the final 2 equations,"},{"Start":"03:10.055 ","End":"03:15.270","Text":"we get calcium plus lead^2+ plus,"},{"Start":"03:15.270 ","End":"03:22.930","Text":"the 2 electrons cancels and the other side we get lead plus calcium^2+,"},{"Start":"03:22.930 ","End":"03:24.540","Text":"so here\u0027s our equation."},{"Start":"03:24.540 ","End":"03:29.375","Text":"When we add these 2 electrode potentials, this 1 and this 1,"},{"Start":"03:29.375 ","End":"03:36.449","Text":"we get E^0 for the cell to be 2.74 volts."},{"Start":"03:42.230 ","End":"03:46.453","Text":"Now, E^0 is positive,"},{"Start":"03:46.453 ","End":"03:50.975","Text":"that means that Delta G is negative so the reaction is spontaneous."},{"Start":"03:50.975 ","End":"03:54.000","Text":"It should go from left to right."},{"Start":"03:56.780 ","End":"03:59.330","Text":"That means calcium is"},{"Start":"03:59.330 ","End":"04:05.015","Text":"a stronger reducing agent than lead because it\u0027s going from left to right."},{"Start":"04:05.015 ","End":"04:07.550","Text":"Calcium is becoming oxidized,"},{"Start":"04:07.550 ","End":"04:11.285","Text":"so it is a strong reducing agent."},{"Start":"04:11.285 ","End":"04:13.265","Text":"Here\u0027s the second example."},{"Start":"04:13.265 ","End":"04:21.760","Text":"The couple Fe^2+ and Fe^3+ has an electrode potential 0.771 volts."},{"Start":"04:21.760 ","End":"04:27.440","Text":"Now the couple of silver and silver^+, it\u0027s 0.800 volts."},{"Start":"04:27.440 ","End":"04:34.445","Text":"We\u0027re asked which is a stronger oxidizing agent, Fe^3+ or Ag^+?"},{"Start":"04:34.445 ","End":"04:39.494","Text":"Now the more positive 1 is that for silver,"},{"Start":"04:39.494 ","End":"04:44.278","Text":"and the oxidized form here is silver^+,"},{"Start":"04:44.278 ","End":"04:47.720","Text":"so Ag^+ should be the stronger oxidizing agent."},{"Start":"04:47.720 ","End":"04:50.565","Text":"Let\u0027s test whether that\u0027s so."},{"Start":"04:50.565 ","End":"04:55.775","Text":"We write the equation for Ag^+ plus electron we get to silver,"},{"Start":"04:55.775 ","End":"05:02.815","Text":"we get E^0 is 0.800 volts and it\u0027s positive sign."},{"Start":"05:02.815 ","End":"05:05.880","Text":"We get iron^3+ plus electron,"},{"Start":"05:05.880 ","End":"05:10.470","Text":"giving us iron^2+ and the electrode potential of"},{"Start":"05:10.470 ","End":"05:15.885","Text":"that is 0.771 volts with a positive sign."},{"Start":"05:15.885 ","End":"05:19.139","Text":"Now if we turn this 1 around,"},{"Start":"05:19.139 ","End":"05:23.060","Text":"Fe^2+ going to Fe^3+ plus an electron."},{"Start":"05:23.060 ","End":"05:26.270","Text":"Here it was reduction and now it\u0027s oxidation,"},{"Start":"05:26.270 ","End":"05:28.955","Text":"this is reduction, of course."},{"Start":"05:28.955 ","End":"05:34.385","Text":"When we add the first equation and the third equation,"},{"Start":"05:34.385 ","End":"05:43.055","Text":"we get Ag^+ plus Fe^2+ the electron cancels,"},{"Start":"05:43.055 ","End":"05:47.323","Text":"giving us Ag plus Fe^3+,"},{"Start":"05:47.323 ","End":"05:49.190","Text":"so here\u0027s the equation."},{"Start":"05:49.190 ","End":"05:57.700","Text":"If we add 0.800 plus minus 0.771,"},{"Start":"05:57.700 ","End":"06:02.070","Text":"then we get 0.029 volts."},{"Start":"06:02.070 ","End":"06:04.910","Text":"E^0 for the cell is positive,"},{"Start":"06:04.910 ","End":"06:07.693","Text":"that means Delta G is negative,"},{"Start":"06:07.693 ","End":"06:13.325","Text":"so the reaction is spontaneous and Ag^+ is a better oxidizing agent than Fe^3+."},{"Start":"06:13.325 ","End":"06:19.280","Text":"Ag^+ is going to Ag."},{"Start":"06:19.280 ","End":"06:25.325","Text":"Ag plus is a better oxidizing agents and Fe^3+."},{"Start":"06:25.325 ","End":"06:30.630","Text":"In this video, we learned about the electrochemical series."}],"ID":33695},{"Watched":false,"Name":"Exercise 1","Duration":"3m 37s","ChapterTopicVideoID":31561,"CourseChapterTopicPlaylistID":286840,"HasSubtitles":false,"ThumbnailPath":null,"UploadDate":null,"DurationForVideoObject":null,"Description":null,"MetaTitle":null,"MetaDescription":null,"Canonical":null,"VideoComments":[],"Subtitles":[],"ID":33696},{"Watched":false,"Name":"Exercise 2","Duration":"4m 29s","ChapterTopicVideoID":31558,"CourseChapterTopicPlaylistID":286840,"HasSubtitles":false,"ThumbnailPath":null,"UploadDate":null,"DurationForVideoObject":null,"Description":null,"MetaTitle":null,"MetaDescription":null,"Canonical":null,"VideoComments":[],"Subtitles":[],"ID":33697},{"Watched":false,"Name":"Exercise 3","Duration":"4m 33s","ChapterTopicVideoID":31559,"CourseChapterTopicPlaylistID":286840,"HasSubtitles":false,"ThumbnailPath":null,"UploadDate":null,"DurationForVideoObject":null,"Description":null,"MetaTitle":null,"MetaDescription":null,"Canonical":null,"VideoComments":[],"Subtitles":[],"ID":33698},{"Watched":false,"Name":"Exercise 4","Duration":"4m 44s","ChapterTopicVideoID":31560,"CourseChapterTopicPlaylistID":286840,"HasSubtitles":false,"ThumbnailPath":null,"UploadDate":null,"DurationForVideoObject":null,"Description":null,"MetaTitle":null,"MetaDescription":null,"Canonical":null,"VideoComments":[],"Subtitles":[],"ID":33699},{"Watched":false,"Name":"Activity series of metals","Duration":"5m 54s","ChapterTopicVideoID":28661,"CourseChapterTopicPlaylistID":286840,"HasSubtitles":true,"ThumbnailPath":null,"UploadDate":null,"DurationForVideoObject":null,"Description":null,"MetaTitle":null,"MetaDescription":null,"Canonical":null,"VideoComments":[],"Subtitles":[{"Start":"00:00.020 ","End":"00:02.235","Text":"In the previous video,"},{"Start":"00:02.235 ","End":"00:04.847","Text":"we learned about the electrochemical series,"},{"Start":"00:04.847 ","End":"00:07.830","Text":"and in this video we\u0027ll study the related series,"},{"Start":"00:07.830 ","End":"00:10.680","Text":"the activity series of metals."},{"Start":"00:10.680 ","End":"00:14.940","Text":"Now the activity series of metals rank some metals according"},{"Start":"00:14.940 ","End":"00:19.515","Text":"to their ability to displace one another from solutions."},{"Start":"00:19.515 ","End":"00:22.800","Text":"The series is essentially the inverse of"},{"Start":"00:22.800 ","End":"00:27.345","Text":"the electrochemical series with the strongest metallic reducing agents,"},{"Start":"00:27.345 ","End":"00:31.605","Text":"the most reactive metal at the top."},{"Start":"00:31.605 ","End":"00:35.820","Text":"Now lithium is the top rather than the bottom,"},{"Start":"00:35.820 ","End":"00:41.135","Text":"and these all have negative electrode potentials."},{"Start":"00:41.135 ","End":"00:44.690","Text":"Here\u0027s 0 and then positive."},{"Start":"00:44.690 ","End":"00:52.880","Text":"The metals at the top from lithium to sodium can displace hydrogen gas from water,"},{"Start":"00:52.880 ","End":"00:54.560","Text":"and of course also from acid,"},{"Start":"00:54.560 ","End":"00:56.945","Text":"but it\u0027s rather violent reaction."},{"Start":"00:56.945 ","End":"00:59.510","Text":"Then from magnesium to iron,"},{"Start":"00:59.510 ","End":"01:03.110","Text":"they can displace hydrogen only from steam,"},{"Start":"01:03.110 ","End":"01:05.090","Text":"not just cold water,"},{"Start":"01:05.090 ","End":"01:10.280","Text":"and of course also from acids because they have negative electrode potentials."},{"Start":"01:10.280 ","End":"01:15.020","Text":"Then cadmium to lead can displace hydrogen from acid,"},{"Start":"01:15.020 ","End":"01:17.060","Text":"but not from water."},{"Start":"01:17.060 ","End":"01:19.070","Text":"Then we have hydrogen,"},{"Start":"01:19.070 ","End":"01:22.948","Text":"the center which has electric potential of 0 and then"},{"Start":"01:22.948 ","End":"01:27.125","Text":"those at the bottom have a positive electrode potential,"},{"Start":"01:27.125 ","End":"01:31.400","Text":"and they can\u0027t displace hydrogen from the acid."},{"Start":"01:31.400 ","End":"01:36.740","Text":"The most reactive metals displace hydrogen from water."},{"Start":"01:36.740 ","End":"01:40.550","Text":"Here\u0027s an example, lithium reacting with water"},{"Start":"01:40.550 ","End":"01:44.734","Text":"to give us lithium hydroxide and hydrogen gas."},{"Start":"01:44.734 ","End":"01:47.545","Text":"Now here\u0027s the oxidation state."},{"Start":"01:47.545 ","End":"01:50.795","Text":"Lithium going to lithium plus,"},{"Start":"01:50.795 ","End":"01:53.750","Text":"and here in order to balance the equation,"},{"Start":"01:53.750 ","End":"01:56.720","Text":"we have 2 lithium giving 2 lithium^plus,"},{"Start":"01:56.720 ","End":"01:58.025","Text":"plus 2 electrons,"},{"Start":"01:58.025 ","End":"02:00.529","Text":"but E^0 does not change."},{"Start":"02:00.529 ","End":"02:05.090","Text":"We\u0027ve taken the E^0, which is negative and inverted"},{"Start":"02:05.090 ","End":"02:10.385","Text":"the equation so that E^0 now becomes positive."},{"Start":"02:10.385 ","End":"02:13.145","Text":"Here\u0027s the reduction step."},{"Start":"02:13.145 ","End":"02:15.545","Text":"Water plus 2 electrons,"},{"Start":"02:15.545 ","End":"02:20.290","Text":"giving us hydrogen gas and 2 OH^minus."},{"Start":"02:20.290 ","End":"02:23.265","Text":"We\u0027re getting hydroxide."},{"Start":"02:23.265 ","End":"02:29.160","Text":"E^0 for this is negative minus 0.828."},{"Start":"02:29.160 ","End":"02:31.810","Text":"Now if we add these 2,"},{"Start":"02:31.810 ","End":"02:35.840","Text":"we get a positive number E^0 is positive."},{"Start":"02:35.840 ","End":"02:39.455","Text":"That means the reaction is spontaneous and"},{"Start":"02:39.455 ","End":"02:45.170","Text":"lithium is indeed reacting with water to give us hydrogen gas."},{"Start":"02:45.170 ","End":"02:50.840","Text":"Now the slightly less active metals require heat to displace hydrogen from water."},{"Start":"02:50.840 ","End":"02:53.195","Text":"I\u0027m not going to discuss that here."},{"Start":"02:53.195 ","End":"02:58.205","Text":"The metals with negative E^0 to displace hydrogen from acid."},{"Start":"02:58.205 ","End":"03:00.440","Text":"So we have some metals,"},{"Start":"03:00.440 ","End":"03:01.670","Text":"as we saw before,"},{"Start":"03:01.670 ","End":"03:05.465","Text":"they displace hydrogen from acid but not from water."},{"Start":"03:05.465 ","End":"03:07.490","Text":"Here\u0027s an example."},{"Start":"03:07.490 ","End":"03:15.300","Text":"Iron reacts with H^plus to give us hydrogen gas and Fe^2 plus."},{"Start":"03:15.320 ","End":"03:22.845","Text":"The oxidation step is Fe going to Fe^2 plus, plus 2 electrons."},{"Start":"03:22.845 ","End":"03:25.580","Text":"I\u0027ve inverted electrode potential,"},{"Start":"03:25.580 ","End":"03:30.275","Text":"which you remember always talks about reduction reactions."},{"Start":"03:30.275 ","End":"03:35.015","Text":"This is oxidation and E^0 is now positive rather than negative."},{"Start":"03:35.015 ","End":"03:37.560","Text":"Reduction step is 2 H^plus,"},{"Start":"03:37.560 ","End":"03:40.250","Text":"plus 2 electrons to give us hydrogen gas."},{"Start":"03:40.250 ","End":"03:43.865","Text":"E^0 for this is of course 0."},{"Start":"03:43.865 ","End":"03:46.610","Text":"Now if I add these 2 numbers,"},{"Start":"03:46.610 ","End":"03:48.530","Text":"then it\u0027s obviously positive."},{"Start":"03:48.530 ","End":"03:52.100","Text":"So the reaction is spontaneous and iron"},{"Start":"03:52.100 ","End":"03:56.930","Text":"reacts with H^plus reacts with an acid to give us hydrogen gas."},{"Start":"03:56.930 ","End":"03:59.275","Text":"Now the metals was positive E^0."},{"Start":"03:59.275 ","End":"04:04.105","Text":"Do not displace hydrogen from acid only those with negative E^0."},{"Start":"04:04.105 ","End":"04:08.360","Text":"Now we\u0027re going to show that metals that are higher up in the series can"},{"Start":"04:08.360 ","End":"04:13.380","Text":"replace metals in solution that are lower down in the series."},{"Start":"04:13.450 ","End":"04:23.705","Text":"Here\u0027s an example, copper reacting with Ag^plus to give us silver metal and Cu^2 plus."},{"Start":"04:23.705 ","End":"04:29.975","Text":"Copper is replacing the silver plus to form Cu^2 plus."},{"Start":"04:29.975 ","End":"04:31.775","Text":"Here is the oxidation step."},{"Start":"04:31.775 ","End":"04:33.590","Text":"Copper to Cu^2 plus,"},{"Start":"04:33.590 ","End":"04:34.970","Text":"plus 2 electrons,"},{"Start":"04:34.970 ","End":"04:41.570","Text":"E^0 so this is minus 0.340 volts because we\u0027ve inverted"},{"Start":"04:41.570 ","End":"04:44.150","Text":"the reaction where we write"},{"Start":"04:44.150 ","End":"04:49.625","Text":"the electrode potentials Cu^2 plus to copper and we\u0027ve turned it around."},{"Start":"04:49.625 ","End":"04:53.060","Text":"The reduction step is 2 Ag^plus,"},{"Start":"04:53.060 ","End":"04:59.780","Text":"plus 2 electrons to give us 2 silver and that solid form, silver metal."},{"Start":"04:59.780 ","End":"05:05.610","Text":"E^0 for this is plus 0.800 volts."},{"Start":"05:05.960 ","End":"05:08.360","Text":"We add these 2 numbers,"},{"Start":"05:08.360 ","End":"05:10.070","Text":"we get a positive number,"},{"Start":"05:10.070 ","End":"05:12.200","Text":"so E^0 is positive."},{"Start":"05:12.200 ","End":"05:14.615","Text":"That means the reaction is spontaneous."},{"Start":"05:14.615 ","End":"05:22.805","Text":"That means that copper is replacing silver in the solution."},{"Start":"05:22.805 ","End":"05:29.270","Text":"If you remember, copper is higher up than silver in the table."},{"Start":"05:29.270 ","End":"05:33.070","Text":"Here\u0027s copper and here\u0027s silver."},{"Start":"05:33.070 ","End":"05:35.840","Text":"But if we look at the copper and zinc,"},{"Start":"05:35.840 ","End":"05:39.230","Text":"will see that zinc is higher than copper."},{"Start":"05:39.230 ","End":"05:44.315","Text":"Zinc replace copper, but copper cannot replace zinc."},{"Start":"05:44.315 ","End":"05:49.870","Text":"This is the basis with Daniell cell, zinc replacing copper."},{"Start":"05:49.870 ","End":"05:54.780","Text":"In this video, we started the activity series of metals."}],"ID":33700}],"Thumbnail":null,"ID":286840},{"Name":"Standard Potentials and Gibbs Free Energy","TopicPlaylistFirstVideoID":0,"Duration":null,"Videos":[{"Watched":false,"Name":"Cell Potential and Gibbs Free Energy","Duration":"6m 55s","ChapterTopicVideoID":28659,"CourseChapterTopicPlaylistID":286841,"HasSubtitles":true,"ThumbnailPath":null,"UploadDate":null,"DurationForVideoObject":null,"Description":null,"MetaTitle":null,"MetaDescription":null,"Canonical":null,"VideoComments":[],"Subtitles":[{"Start":"00:00.000 ","End":"00:01.650","Text":"In previous videos,"},{"Start":"00:01.650 ","End":"00:05.910","Text":"we talked about the cell potential and its connection with the Gibbs free energy."},{"Start":"00:05.910 ","End":"00:10.365","Text":"In this video, we\u0027ll derive the expression for the relation between them."},{"Start":"00:10.365 ","End":"00:13.229","Text":"We start by describing"},{"Start":"00:13.229 ","End":"00:18.225","Text":"the relation between the potential difference and the Gibbs free energy."},{"Start":"00:18.225 ","End":"00:20.040","Text":"Now in thermodynamics,"},{"Start":"00:20.040 ","End":"00:23.130","Text":"we showed that Delta G is equal to W_e,"},{"Start":"00:23.130 ","End":"00:26.520","Text":"where W_e is the maximum non-expansion work"},{"Start":"00:26.520 ","End":"00:29.745","Text":"that a reaction can do at constant pressure and volume."},{"Start":"00:29.745 ","End":"00:35.040","Text":"That\u0027s all the work apart from PV work."},{"Start":"00:35.040 ","End":"00:40.115","Text":"Now when n moles of electrons travels through a potential difference E,"},{"Start":"00:40.115 ","End":"00:46.615","Text":"the work done is W_e equal to the total charge times the potential difference."},{"Start":"00:46.615 ","End":"00:52.385","Text":"Now the charge of 1 mole of electrons is minus e times N_A."},{"Start":"00:52.385 ","End":"00:54.169","Text":"e is electron charge."},{"Start":"00:54.169 ","End":"00:56.585","Text":"N is Avogadro\u0027s constant."},{"Start":"00:56.585 ","End":"00:59.420","Text":"The total charge is minus n,"},{"Start":"00:59.420 ","End":"01:01.040","Text":"n is the number of moles,"},{"Start":"01:01.040 ","End":"01:03.215","Text":"times e, the electron charge,"},{"Start":"01:03.215 ","End":"01:06.440","Text":"times N_A, Avogadro\u0027s constant."},{"Start":"01:06.440 ","End":"01:09.364","Text":"Now we\u0027re going to define Faraday\u0027s constant."},{"Start":"01:09.364 ","End":"01:11.395","Text":"Faraday\u0027s constant, F=e*N_A."},{"Start":"01:11.395 ","End":"01:19.960","Text":"e is 1.602177*10^-19 Coulombs,"},{"Start":"01:19.960 ","End":"01:27.525","Text":"and N_A is 6.0223*10^23 per mole."},{"Start":"01:27.525 ","End":"01:29.340","Text":"It can be electrons per mole,"},{"Start":"01:29.340 ","End":"01:31.575","Text":"all sorts of things per mole."},{"Start":"01:31.575 ","End":"01:33.780","Text":"When we multiply this out,"},{"Start":"01:33.780 ","End":"01:39.290","Text":"we get 9.6485*10^4 Coulombs per mole."},{"Start":"01:39.290 ","End":"01:42.925","Text":"Of course, it\u0027s mole of electrons here."},{"Start":"01:42.925 ","End":"01:49.590","Text":"Here\u0027s our value of F. We can write that W_e is equal"},{"Start":"01:49.590 ","End":"01:57.555","Text":"to the total charge -neN_A times E. That\u0027s minus n,"},{"Start":"01:57.555 ","End":"02:06.675","Text":"eN_A is F, so that\u0027s F*E. We have W_e equal to minus nFE."},{"Start":"02:06.675 ","End":"02:10.110","Text":"That means that Delta G,"},{"Start":"02:10.110 ","End":"02:12.150","Text":"which we saw was before,"},{"Start":"02:12.150 ","End":"02:16.990","Text":"was equal to W_e is equal to minus nFE."},{"Start":"02:16.990 ","End":"02:22.265","Text":"Now we have the connection between thermodynamics and electrochemistry."},{"Start":"02:22.265 ","End":"02:24.373","Text":"Delta G is thermodynamics,"},{"Start":"02:24.373 ","End":"02:26.915","Text":"and E is electrochemistry."},{"Start":"02:26.915 ","End":"02:31.530","Text":"The units are mole for the n,"},{"Start":"02:31.530 ","End":"02:34.320","Text":"Coulomb per mole for the F,"},{"Start":"02:34.320 ","End":"02:36.510","Text":"and V for E,"},{"Start":"02:36.510 ","End":"02:40.680","Text":"volts for E. When we multiply that out,"},{"Start":"02:40.680 ","End":"02:43.815","Text":"we get mole*mole^-1 is 1,"},{"Start":"02:43.815 ","End":"02:47.580","Text":"Coulomb times volts is equal to Joules."},{"Start":"02:47.580 ","End":"02:50.805","Text":"Now sometimes we need Delta G_r,"},{"Start":"02:50.805 ","End":"02:54.375","Text":"that\u0027s with the units of joules per mole,"},{"Start":"02:54.375 ","End":"02:55.640","Text":"and if we need that,"},{"Start":"02:55.640 ","End":"02:58.040","Text":"then n is just a number,"},{"Start":"02:58.040 ","End":"03:01.475","Text":"the number of moles without the moles."},{"Start":"03:01.475 ","End":"03:05.930","Text":"Now what\u0027s the connection between the cell potential and Gibbs free energy?"},{"Start":"03:05.930 ","End":"03:12.665","Text":"Now we get the maximum non expansion work when a cell is operating reversibly."},{"Start":"03:12.665 ","End":"03:15.650","Text":"That means that the pushing power of the cell"},{"Start":"03:15.650 ","End":"03:19.595","Text":"has to be matched by an external source of potential."},{"Start":"03:19.595 ","End":"03:22.640","Text":"This can be achieved using a volt meter"},{"Start":"03:22.640 ","End":"03:25.775","Text":"with a high resistance so that no current is drawn."},{"Start":"03:25.775 ","End":"03:30.740","Text":"We can see that from this famous equation, I=V/R."},{"Start":"03:30.740 ","End":"03:33.635","Text":"If the resistance is very high,"},{"Start":"03:33.635 ","End":"03:35.810","Text":"then I will be very small."},{"Start":"03:35.810 ","End":"03:37.840","Text":"I is the current,"},{"Start":"03:37.840 ","End":"03:40.155","Text":"V is the potential,"},{"Start":"03:40.155 ","End":"03:42.825","Text":"and R is the resistance."},{"Start":"03:42.825 ","End":"03:46.010","Text":"Under these circumstances, this is"},{"Start":"03:46.010 ","End":"03:51.340","Text":"the maximum possible potential and it\u0027s called the cell potential, E_cell."},{"Start":"03:51.340 ","End":"03:54.470","Text":"Now the working cell that produces current,"},{"Start":"03:54.470 ","End":"03:58.430","Text":"the potential will be smaller than this, smaller than E_cell."},{"Start":"03:58.430 ","End":"04:03.685","Text":"Delta G_r=-nFE_cell."},{"Start":"04:03.685 ","End":"04:08.950","Text":"For standard conditions we get Delta G_r^0=-nFE^0_cell."},{"Start":"04:12.280 ","End":"04:16.560","Text":"These are important relations."},{"Start":"04:16.730 ","End":"04:23.379","Text":"These are the relations between the cell potential and Gibbs free energy."},{"Start":"04:23.379 ","End":"04:26.880","Text":"Now if E_cell is positive,"},{"Start":"04:26.880 ","End":"04:31.640","Text":"Delta G will be negative and the reaction will be spontaneous."},{"Start":"04:31.640 ","End":"04:33.950","Text":"This is very important."},{"Start":"04:33.950 ","End":"04:41.060","Text":"Positive E cell gives us negative Delta G and a spontaneous reaction."},{"Start":"04:41.060 ","End":"04:43.400","Text":"Here\u0027s an example."},{"Start":"04:43.400 ","End":"04:48.105","Text":"Calculate Delta G^0_cell for the Danielle cell,"},{"Start":"04:48.105 ","End":"04:54.510","Text":"given that E^0_cell is equal to plus 1.103 volts."},{"Start":"04:54.510 ","End":"04:58.800","Text":"The oxidation reaction is zinc metal,"},{"Start":"04:58.800 ","End":"05:01.770","Text":"giving zinc^2+, +2 electrons."},{"Start":"05:01.770 ","End":"05:03.195","Text":"That\u0027s oxidation."},{"Start":"05:03.195 ","End":"05:05.580","Text":"It takes place at the anode."},{"Start":"05:05.580 ","End":"05:07.770","Text":"At the cathode,"},{"Start":"05:07.770 ","End":"05:10.900","Text":"we have reduction Cu^2+,"},{"Start":"05:10.900 ","End":"05:14.775","Text":"+2 electrons to give us copper metal."},{"Start":"05:14.775 ","End":"05:18.110","Text":"N is equal to 2 moles of electrons."},{"Start":"05:18.110 ","End":"05:20.080","Text":"Here we have 2 and 2."},{"Start":"05:20.080 ","End":"05:25.020","Text":"We can write that Delta G^0 is equal to -nFE^0_cell."},{"Start":"05:27.170 ","End":"05:31.245","Text":"N is -2 moles,"},{"Start":"05:31.245 ","End":"05:34.240","Text":"then we have Faraday\u0027s constant,"},{"Start":"05:35.480 ","End":"05:38.070","Text":"9.6485*10^4 Coulombs per mole,"},{"Start":"05:38.070 ","End":"05:41.850","Text":"and then we have the E^0_cell,"},{"Start":"05:41.850 ","End":"05:45.180","Text":"which is 1.103 volts."},{"Start":"05:45.180 ","End":"05:46.830","Text":"If we multiply all this,"},{"Start":"05:46.830 ","End":"05:52.150","Text":"we get 2.128*10^5 Joules."},{"Start":"05:52.250 ","End":"05:58.050","Text":"Moles*moles^-1 is 1, Coulomb*volts is Joules."},{"Start":"05:58.050 ","End":"06:02.060","Text":"Now a word about intensive and extensive properties."},{"Start":"06:02.060 ","End":"06:07.520","Text":"If we multiply the half reactions by 2 or any other number, then N,"},{"Start":"06:07.520 ","End":"06:09.725","Text":"the number of moles will also double,"},{"Start":"06:09.725 ","End":"06:12.230","Text":"and Delta G will also double,"},{"Start":"06:12.230 ","End":"06:15.280","Text":"but the cell potential remains the same."},{"Start":"06:15.280 ","End":"06:18.005","Text":"We can see that from this relationship,"},{"Start":"06:18.005 ","End":"06:22.970","Text":"E_cell is equal to -Delta G divided by nF."},{"Start":"06:22.970 ","End":"06:24.767","Text":"Delta G doubles,"},{"Start":"06:24.767 ","End":"06:26.495","Text":"n will also double,"},{"Start":"06:26.495 ","End":"06:30.425","Text":"and the ratio will remain constant."},{"Start":"06:30.425 ","End":"06:34.370","Text":"E_cell will remain constant even if we"},{"Start":"06:34.370 ","End":"06:39.700","Text":"multiply the reactions by a whole number or by any other number."},{"Start":"06:39.700 ","End":"06:44.030","Text":"We can say that E_cell is an intensive property,"},{"Start":"06:44.030 ","End":"06:47.824","Text":"whereas Delta G^0 is the extensive property."},{"Start":"06:47.824 ","End":"06:50.585","Text":"In this video, we learned about the relation"},{"Start":"06:50.585 ","End":"06:54.540","Text":"between Gibbs free energy and the cell potential."}],"ID":33701},{"Watched":false,"Name":"Exercise 1","Duration":"4m 58s","ChapterTopicVideoID":31557,"CourseChapterTopicPlaylistID":286841,"HasSubtitles":false,"ThumbnailPath":null,"UploadDate":null,"DurationForVideoObject":null,"Description":null,"MetaTitle":null,"MetaDescription":null,"Canonical":null,"VideoComments":[],"Subtitles":[],"ID":33702},{"Watched":false,"Name":"Combining Half-Reactions","Duration":"4m 42s","ChapterTopicVideoID":28660,"CourseChapterTopicPlaylistID":286841,"HasSubtitles":true,"ThumbnailPath":null,"UploadDate":null,"DurationForVideoObject":null,"Description":null,"MetaTitle":null,"MetaDescription":null,"Canonical":null,"VideoComments":[],"Subtitles":[{"Start":"00:00.000 ","End":"00:02.205","Text":"In the previous video,"},{"Start":"00:02.205 ","End":"00:06.719","Text":"we learned about the relation between Gibbs free energy and the cell potential."},{"Start":"00:06.719 ","End":"00:09.810","Text":"In this video, we use the relation to calculate"},{"Start":"00:09.810 ","End":"00:14.355","Text":"an electrode potential from 2 other electrode potentials."},{"Start":"00:14.355 ","End":"00:16.020","Text":"We\u0027re going to calculate"},{"Start":"00:16.020 ","End":"00:20.460","Text":"the standard electrode potential from 2 other electrode potentials."},{"Start":"00:20.460 ","End":"00:22.170","Text":"Here\u0027s an example."},{"Start":"00:22.170 ","End":"00:26.115","Text":"Calculate the standard electrode potential for the 1/2 reaction"},{"Start":"00:26.115 ","End":"00:30.885","Text":"cerium 4+ plus 4 electrons to give us cerium metal."},{"Start":"00:30.885 ","End":"00:34.590","Text":"Given that cerium 3++ 3 electrons to give"},{"Start":"00:34.590 ","End":"00:40.625","Text":"cerium metal as a electrode potential of -2.48 volts."},{"Start":"00:40.625 ","End":"00:49.825","Text":"Cerium 4++ electron giving cerium 3+ has an electrode potential of +1.61 volts."},{"Start":"00:49.825 ","End":"00:52.500","Text":"Let\u0027s add the 2 1/2-reactions."},{"Start":"00:52.500 ","End":"00:56.415","Text":"Cerium 3++ 3 electrons to give cerium."},{"Start":"00:56.415 ","End":"01:00.675","Text":"Cerium 4++ an electron to give you cerium 3+."},{"Start":"01:00.675 ","End":"01:04.275","Text":"Let\u0027s add them, cerium 3+ cancels,"},{"Start":"01:04.275 ","End":"01:06.390","Text":"we get cerium 4+,"},{"Start":"01:06.390 ","End":"01:09.910","Text":"plus 4 electrons to give cerium metal."},{"Start":"01:09.910 ","End":"01:14.390","Text":"Now we can\u0027t just add up the e zeros of these 2 reactions."},{"Start":"01:14.390 ","End":"01:17.605","Text":"We have to first calculate Delta G^0."},{"Start":"01:17.605 ","End":"01:21.735","Text":"Let\u0027s calculate Delta G^0 for each 1/2 reaction."},{"Start":"01:21.735 ","End":"01:25.020","Text":"Now for the first one is -nFE^0,"},{"Start":"01:25.360 ","End":"01:29.810","Text":"and we have 3 moles of electrons involved here."},{"Start":"01:29.810 ","End":"01:32.855","Text":"There\u0027s 3 in the first one and 1 in the second,"},{"Start":"01:32.855 ","End":"01:36.820","Text":"and 4 in the sum."},{"Start":"01:36.820 ","End":"01:40.910","Text":"It\u0027s -3 moles times the Faraday constant,"},{"Start":"01:40.910 ","End":"01:48.110","Text":"9.6485 times 10^4 coulombs per mole times the electric potential."},{"Start":"01:48.110 ","End":"01:51.655","Text":"Electric potential is -2.48 volts."},{"Start":"01:51.655 ","End":"01:53.925","Text":"We have minus times minus,"},{"Start":"01:53.925 ","End":"01:56.910","Text":"and that gives us a positive number."},{"Start":"01:56.910 ","End":"02:00.870","Text":"The moles goes with the moles^-1."},{"Start":"02:00.870 ","End":"02:06.470","Text":"We have coulomb times volts, which is joules."},{"Start":"02:06.470 ","End":"02:13.945","Text":"When we multiply all this out we get 7.179 times 10^5 joules."},{"Start":"02:13.945 ","End":"02:16.925","Text":"We do the same for the second reaction."},{"Start":"02:16.925 ","End":"02:24.455","Text":"Now it\u0027s -1 mole times the Faraday constant and times the E^0 for the second reaction,"},{"Start":"02:24.455 ","End":"02:27.590","Text":"which we saw was 1.61 volt."},{"Start":"02:27.590 ","End":"02:29.180","Text":"I multiply all that out,"},{"Start":"02:29.180 ","End":"02:35.020","Text":"we get -1.553 times 10^5 joules."},{"Start":"02:35.020 ","End":"02:39.785","Text":"Now they have different signs here we have a positive sign and here and negative sign."},{"Start":"02:39.785 ","End":"02:42.275","Text":"Let\u0027s add the Delta G\u0027s."},{"Start":"02:42.275 ","End":"02:48.695","Text":"When we add them we get 5.626 times 10^5 joules."},{"Start":"02:48.695 ","End":"02:51.170","Text":"Now we can go and calculate"},{"Start":"02:51.170 ","End":"02:58.010","Text":"the standard electrode potential for the reaction we\u0027re seeking."},{"Start":"02:58.010 ","End":"03:02.365","Text":"This ones, cerium 4++ plus 4 electrons give us cerium."},{"Start":"03:02.365 ","End":"03:07.880","Text":"That\u0027s equal to Delta G divided by -nF."},{"Start":"03:07.880 ","End":"03:14.055","Text":"Delta G is 5.626 times 10^5 joules,"},{"Start":"03:14.055 ","End":"03:17.580","Text":"and we divide it by minus n is this time"},{"Start":"03:17.580 ","End":"03:22.845","Text":"4 moles minus 4 moles times the Faraday constant,"},{"Start":"03:22.845 ","End":"03:26.610","Text":"and the moles times mole^-1."},{"Start":"03:26.610 ","End":"03:29.300","Text":"We\u0027ve got joules divided by coulomb,"},{"Start":"03:29.300 ","End":"03:30.860","Text":"which is votes,"},{"Start":"03:30.860 ","End":"03:36.184","Text":"and we multiply it out we get -1.406 volts."},{"Start":"03:36.184 ","End":"03:42.080","Text":"Now we could\u0027ve taken a shortcut if we recognize that we\u0027re"},{"Start":"03:42.080 ","End":"03:49.010","Text":"multiplying here by Faraday constant and then dividing by the Faraday constant."},{"Start":"03:49.010 ","End":"03:55.490","Text":"If we just don\u0027t include it just so we can see that E^0 for the reaction we\u0027re"},{"Start":"03:55.490 ","End":"04:02.850","Text":"looking for is 3 times E^0 for the first reaction,"},{"Start":"04:02.850 ","End":"04:05.860","Text":"plus 1 times E^0 for the second reaction."},{"Start":"04:05.860 ","End":"04:09.845","Text":"Here we have 3, 1 divided by 4."},{"Start":"04:09.845 ","End":"04:16.240","Text":"Multiply that out it\u0027s exactly the same as we had before, -1.46 volts."},{"Start":"04:16.240 ","End":"04:18.280","Text":"Now it\u0027s important to note that if"},{"Start":"04:18.280 ","End":"04:22.150","Text":"all the 1/2 equations involves the same number of electrons,"},{"Start":"04:22.150 ","End":"04:25.540","Text":"we can just add the standard electrode potentials,"},{"Start":"04:25.540 ","End":"04:27.240","Text":"this will say 2,"},{"Start":"04:27.240 ","End":"04:30.974","Text":"and again 2 divided by 2 they would all cancel"},{"Start":"04:30.974 ","End":"04:35.445","Text":"and then we could just sum up the electrode potentials."},{"Start":"04:35.445 ","End":"04:41.960","Text":"In this video, we calculated electrode potential from 2 other electrode potentials."}],"ID":33703}],"Thumbnail":null,"ID":286841},{"Name":"Standard Potentials and Equilibrium Constants","TopicPlaylistFirstVideoID":0,"Duration":null,"Videos":[{"Watched":false,"Name":"Standard Cell Potential and Equilibrium Constant","Duration":"6m 11s","ChapterTopicVideoID":28671,"CourseChapterTopicPlaylistID":286842,"HasSubtitles":true,"ThumbnailPath":null,"UploadDate":null,"DurationForVideoObject":null,"Description":null,"MetaTitle":null,"MetaDescription":null,"Canonical":null,"VideoComments":[],"Subtitles":[{"Start":"00:00.020 ","End":"00:04.260","Text":"In previous videos, we talked about the relation between"},{"Start":"00:04.260 ","End":"00:08.490","Text":"standard cell potentials and Gibbs free energy."},{"Start":"00:08.490 ","End":"00:11.970","Text":"In this video, we\u0027ll talk about the relation between"},{"Start":"00:11.970 ","End":"00:16.335","Text":"standard cell potentials and equilibrium constants."},{"Start":"00:16.335 ","End":"00:21.705","Text":"Here\u0027s the relation we found between the standard cell potential and Gibbs free energy."},{"Start":"00:21.705 ","End":"00:27.060","Text":"We saw that Delta G^0_r is = minus nF,"},{"Start":"00:27.060 ","End":"00:30.790","Text":"F is the Faraday constant E^0_cell."},{"Start":"00:31.510 ","End":"00:37.270","Text":"We know the relation between the Gibbs free energy and the equilibrium constant."},{"Start":"00:37.270 ","End":"00:42.950","Text":"There\u0027s Delta G^0_r=minus RTlnK,"},{"Start":"00:42.950 ","End":"00:46.190","Text":"where K is of course is the equilibrium constant."},{"Start":"00:46.190 ","End":"00:49.040","Text":"Now, we can combine these 2 equations to get"},{"Start":"00:49.040 ","End":"00:53.495","Text":"the standard cell potential and the equilibrium constant relation,"},{"Start":"00:53.495 ","End":"00:59.050","Text":"here we have it nFE^0_cell = RTlnK."},{"Start":"00:59.050 ","End":"01:07.380","Text":"From that we can see that lnK=nFE^0_cell divided by RT."},{"Start":"01:07.380 ","End":"01:15.295","Text":"Or we may need E^0_cell equal to RT divided by nFlnK."},{"Start":"01:15.295 ","End":"01:21.125","Text":"Now we have the relationship between K and the cell potential."},{"Start":"01:21.125 ","End":"01:27.560","Text":"Now, if we\u0027re doing experiments at 25 degrees Celsius,"},{"Start":"01:27.560 ","End":"01:33.680","Text":"RT divided by F=R is 8.3145 Joules per"},{"Start":"01:33.680 ","End":"01:39.810","Text":"mole per K. Then at 25 degrees Celsius,"},{"Start":"01:39.810 ","End":"01:45.660","Text":"T=298.15 K and F"},{"Start":"01:45.660 ","End":"01:51.065","Text":"is 96,485 Coulomb per mole."},{"Start":"01:51.065 ","End":"01:56.930","Text":"Now, if we multiply all these numbers, we get 0.025693."},{"Start":"01:56.930 ","End":"01:59.315","Text":"What about the units?"},{"Start":"01:59.315 ","End":"02:02.285","Text":"K^-1 goes with K,"},{"Start":"02:02.285 ","End":"02:08.555","Text":"mole^-1 goes with mole^-1 and we\u0027re left with joules divided by Coulomb."},{"Start":"02:08.555 ","End":"02:13.570","Text":"We know that Joules divided by Coulomb is equal to volts."},{"Start":"02:13.570 ","End":"02:19.605","Text":"We\u0027re left with 0.025693 volts."},{"Start":"02:19.605 ","End":"02:21.820","Text":"That\u0027s our volume."},{"Start":"02:21.820 ","End":"02:29.705","Text":"Now, we can write that 25 degrees Celsius E^0_cell=RT divided by"},{"Start":"02:29.705 ","End":"02:39.175","Text":"nFlnK and that\u0027s 0.0257 divided by n volts times lnK."},{"Start":"02:39.175 ","End":"02:44.615","Text":"Because if you remember what we worked out up here was RT divided by F,"},{"Start":"02:44.615 ","End":"02:48.610","Text":"and that was 0.0257 volts."},{"Start":"02:48.610 ","End":"02:52.580","Text":"Or we can turn this around and see that"},{"Start":"02:52.580 ","End":"03:00.775","Text":"lnK=nE^0_cell divided by 0.0257 volts."},{"Start":"03:00.775 ","End":"03:03.225","Text":"We have 2 relationships."},{"Start":"03:03.225 ","End":"03:06.210","Text":"E cell is equal to this,"},{"Start":"03:06.210 ","End":"03:08.640","Text":"our lnK is equal to this."},{"Start":"03:08.640 ","End":"03:15.964","Text":"Now, supposing E_cell is greater than 0, then it\u0027s positive."},{"Start":"03:15.964 ","End":"03:18.435","Text":"The lnK will also be positive."},{"Start":"03:18.435 ","End":"03:21.105","Text":"Because it\u0027s a log relationship,"},{"Start":"03:21.105 ","End":"03:24.195","Text":"K will be much greater than 1."},{"Start":"03:24.195 ","End":"03:28.365","Text":"If on the other hand, E_cell is negative,"},{"Start":"03:28.365 ","End":"03:33.940","Text":"lnK will be negative and K will be much much less than 1."},{"Start":"03:33.940 ","End":"03:37.300","Text":"This means the reaction has gone to completion,"},{"Start":"03:37.300 ","End":"03:39.740","Text":"and this it is barely started."},{"Start":"03:39.740 ","End":"03:45.770","Text":"Now, we can calculate K for any reaction that can be written as a sum of 2.5 reactions."},{"Start":"03:45.770 ","End":"03:50.035","Text":"Any reaction where we can find the E_cell,"},{"Start":"03:50.035 ","End":"03:54.815","Text":"the cell potential, we can find the equilibrium constant."},{"Start":"03:54.815 ","End":"03:58.250","Text":"Here\u0027s an example. Calculate K,"},{"Start":"03:58.250 ","End":"04:02.045","Text":"the equilibrium constant for the Daniell cell reaction."},{"Start":"04:02.045 ","End":"04:05.839","Text":"We know that the anode,"},{"Start":"04:05.839 ","End":"04:10.250","Text":"the oxidation is Zn zinc to zinc 2 plus,"},{"Start":"04:10.250 ","End":"04:13.135","Text":"plus 2 electrons, that\u0027s the oxidation."},{"Start":"04:13.135 ","End":"04:17.085","Text":"We know that reduction is copper 2 plus,"},{"Start":"04:17.085 ","End":"04:19.865","Text":"plus 2 electrons to give us copper."},{"Start":"04:19.865 ","End":"04:24.895","Text":"We see from the 2 electrons that n is = 2."},{"Start":"04:24.895 ","End":"04:29.610","Text":"E cell is E^0 for the cathode,"},{"Start":"04:29.610 ","End":"04:36.665","Text":"that\u0027s a reduction step minus E^0 for the anode which is the oxidation step."},{"Start":"04:36.665 ","End":"04:45.675","Text":"That\u0027s E^0 for the copper 2 plus/copper minus E^0 for zinc 2 plus/zinc."},{"Start":"04:45.675 ","End":"04:52.140","Text":"These numbers are 0.340 volts for the copper"},{"Start":"04:52.140 ","End":"04:59.700","Text":"minus 0.763 minus is for the zinc."},{"Start":"04:59.700 ","End":"05:01.230","Text":"When we work this out,"},{"Start":"05:01.230 ","End":"05:03.795","Text":"we get 1.103 volts."},{"Start":"05:03.795 ","End":"05:08.070","Text":"That\u0027s what was measured if for the Daniell cell."},{"Start":"05:08.070 ","End":"05:10.080","Text":"Now we can see that"},{"Start":"05:10.080 ","End":"05:19.380","Text":"lnK=nE^0_cell divided by 0.0257 volts."},{"Start":"05:19.380 ","End":"05:22.980","Text":"What\u0027s that? N is 2,"},{"Start":"05:22.980 ","End":"05:27.820","Text":"E^0_cell is 1.103 volts."},{"Start":"05:28.040 ","End":"05:34.250","Text":"Here we have on the denominator 0.0257 volts."},{"Start":"05:34.250 ","End":"05:36.440","Text":"The volts cancel."},{"Start":"05:36.440 ","End":"05:42.540","Text":"That gives us 85.8. lnK"},{"Start":"05:42.540 ","End":"05:48.600","Text":"is 85.84 which means that K is e to the power 8.845."},{"Start":"05:48.600 ","End":"05:50.255","Text":"That\u0027s a very large number,"},{"Start":"05:50.255 ","End":"05:54.265","Text":"is 1.90 times 10^37."},{"Start":"05:54.265 ","End":"05:59.595","Text":"We can certainly say that K is much greater than 1."},{"Start":"05:59.595 ","End":"06:03.105","Text":"The reaction certainly goes to completion."},{"Start":"06:03.105 ","End":"06:06.260","Text":"In this video, we talked about the relationship between"},{"Start":"06:06.260 ","End":"06:10.200","Text":"cell potential and the equilibrium constant."}],"ID":33704},{"Watched":false,"Name":"Exercise 1 part a","Duration":"3m 45s","ChapterTopicVideoID":31565,"CourseChapterTopicPlaylistID":286842,"HasSubtitles":false,"ThumbnailPath":null,"UploadDate":null,"DurationForVideoObject":null,"Description":null,"MetaTitle":null,"MetaDescription":null,"Canonical":null,"VideoComments":[],"Subtitles":[],"ID":33705},{"Watched":false,"Name":"Exercise 1 part b","Duration":"2m 4s","ChapterTopicVideoID":31562,"CourseChapterTopicPlaylistID":286842,"HasSubtitles":false,"ThumbnailPath":null,"UploadDate":null,"DurationForVideoObject":null,"Description":null,"MetaTitle":null,"MetaDescription":null,"Canonical":null,"VideoComments":[],"Subtitles":[],"ID":33706},{"Watched":false,"Name":"Exercise 1 part c","Duration":"4m 2s","ChapterTopicVideoID":31563,"CourseChapterTopicPlaylistID":286842,"HasSubtitles":false,"ThumbnailPath":null,"UploadDate":null,"DurationForVideoObject":null,"Description":null,"MetaTitle":null,"MetaDescription":null,"Canonical":null,"VideoComments":[],"Subtitles":[],"ID":33707},{"Watched":false,"Name":"Cell Potential for Non-Standard Concentrations","Duration":"5m 3s","ChapterTopicVideoID":28670,"CourseChapterTopicPlaylistID":286842,"HasSubtitles":true,"ThumbnailPath":null,"UploadDate":null,"DurationForVideoObject":null,"Description":null,"MetaTitle":null,"MetaDescription":null,"Canonical":null,"VideoComments":[],"Subtitles":[{"Start":"00:00.000 ","End":"00:02.250","Text":"In a previous video,"},{"Start":"00:02.250 ","End":"00:04.170","Text":"we learned about the connection between"},{"Start":"00:04.170 ","End":"00:08.205","Text":"the standard cell potential and the equilibrium constant."},{"Start":"00:08.205 ","End":"00:14.580","Text":"In this video, we\u0027ll learn about the case when the concentrations are non-standard."},{"Start":"00:14.580 ","End":"00:20.960","Text":"Now, from previous studies of the equilibrium and thermodynamics,"},{"Start":"00:20.960 ","End":"00:27.705","Text":"we found that Delta G_r equal to Delta G^0_r+RT Ln Q,"},{"Start":"00:27.705 ","End":"00:31.140","Text":"where Q is the reaction quotient."},{"Start":"00:31.140 ","End":"00:41.735","Text":"Now, if we substitute Delta G_r= -nFE_cell and Delta G_r for the standard case,"},{"Start":"00:41.735 ","End":"00:45.845","Text":"0 equal to minus nFE^0_cell."},{"Start":"00:45.845 ","End":"00:50.210","Text":"We substitute these two expressions in this one,"},{"Start":"00:50.210 ","End":"00:55.100","Text":"we get minus nFE_cell,"},{"Start":"00:55.100 ","End":"01:00.805","Text":"that\u0027s instead of Delta G_r= -nFE^0_cell."},{"Start":"01:00.805 ","End":"01:07.645","Text":"That\u0027s instead of Delta G_r 0+RT Ln Q."},{"Start":"01:07.645 ","End":"01:12.125","Text":"If we divide the whole thing by minus nF,"},{"Start":"01:12.125 ","End":"01:15.785","Text":"we get E_cell=E^0_"},{"Start":"01:15.785 ","End":"01:23.625","Text":"cell-RTF Ln Q."},{"Start":"01:23.625 ","End":"01:31.380","Text":"Is a very famous equations called the Nernst equation and was written in 1889."},{"Start":"01:31.390 ","End":"01:36.575","Text":"We\u0027re going to use this equation quite a number of times."},{"Start":"01:36.575 ","End":"01:47.740","Text":"We saw in a previous video that at 25 degrees Celsius, RT/F=0.0257 volts."},{"Start":"01:47.740 ","End":"01:55.910","Text":"We can write the E_cell=E_cell 0-RTF Ln Q."},{"Start":"01:55.910 ","End":"01:58.100","Text":"Instead of writing that,"},{"Start":"01:58.100 ","End":"02:02.490","Text":"we can substitute for RT/F, this value."},{"Start":"02:02.490 ","End":"02:11.790","Text":"We get E_cell=E_cell 0-0.0257 volts and we still have the n,"},{"Start":"02:11.790 ","End":"02:17.490","Text":"so here is the n. Now we have"},{"Start":"02:17.490 ","End":"02:26.590","Text":"E_cell=E0_cell-0.0257 volts Ln Q."},{"Start":"02:26.960 ","End":"02:29.835","Text":"Here\u0027s an example."},{"Start":"02:29.835 ","End":"02:36.470","Text":"Calculate E_cell for Daniell cell where the concentration of copper 2 plus is"},{"Start":"02:36.470 ","End":"02:43.520","Text":"1.5 molar and the concentration of zinc 2 plus 0.15 molar."},{"Start":"02:43.520 ","End":"02:51.120","Text":"We\u0027re told that the standard cell is 1.103 volts."},{"Start":"02:51.140 ","End":"02:53.955","Text":"Here\u0027s our total reaction."},{"Start":"02:53.955 ","End":"03:02.330","Text":"Zinc+copper 2+ and we\u0027re given the concentration 1.5 molar."},{"Start":"03:02.330 ","End":"03:11.290","Text":"Going to copper+zinc 2+ and here the concentration 0.15 molar."},{"Start":"03:12.470 ","End":"03:15.590","Text":"We can work out Q."},{"Start":"03:15.590 ","End":"03:17.810","Text":"Remember it\u0027s just like K,"},{"Start":"03:17.810 ","End":"03:21.365","Text":"except that it\u0027s valid for any concentrations."},{"Start":"03:21.365 ","End":"03:29.435","Text":"Q is equal to Zn 2+ concentration divided by Cu 2+ concentration."},{"Start":"03:29.435 ","End":"03:33.440","Text":"The solids, the metals aren\u0027t included."},{"Start":"03:33.440 ","End":"03:36.035","Text":"The activity for them is just 1."},{"Start":"03:36.035 ","End":"03:41.720","Text":"We have 0.15 molar/1.5 molar,"},{"Start":"03:41.720 ","End":"03:45.835","Text":"which is just 0.10."},{"Start":"03:45.835 ","End":"03:52.240","Text":"If we work out the Ln, Ln of Q=-2.30."},{"Start":"03:52.520 ","End":"03:57.779","Text":"E_cell=1.103 volts."},{"Start":"03:57.779 ","End":"04:00.430","Text":"That\u0027s for the value for E^0,"},{"Start":"04:00.970 ","End":"04:08.480","Text":"minus 0.0257 volts, we have to divide by the right value"},{"Start":"04:08.480 ","End":"04:15.715","Text":"of n. We see that the right value is 2 because we have 2+ so we need 2 electrons."},{"Start":"04:15.715 ","End":"04:22.750","Text":"Divide by 2 times minus 2.30 Ln Q."},{"Start":"04:23.660 ","End":"04:29.580","Text":"Work that out, we get 1.103 volts for the first part,"},{"Start":"04:29.580 ","End":"04:35.280","Text":"plus, this minus times minus 0.029 volts."},{"Start":"04:35.280 ","End":"04:40.455","Text":"We add these two we\u0027ve got 1.132 volts."},{"Start":"04:40.455 ","End":"04:49.450","Text":"We can see that the E_cell potential here is greater than the standard cell potential."},{"Start":"04:49.450 ","End":"04:52.475","Text":"Since E_cell is positive,"},{"Start":"04:52.475 ","End":"04:55.655","Text":"we can see that the reaction is spontaneous."},{"Start":"04:55.655 ","End":"05:02.580","Text":"In this video, we learned about the Nernst equation for non-standard concentrations."}],"ID":33708},{"Watched":false,"Name":"Exercise 2","Duration":"7m 44s","ChapterTopicVideoID":31564,"CourseChapterTopicPlaylistID":286842,"HasSubtitles":false,"ThumbnailPath":null,"UploadDate":null,"DurationForVideoObject":null,"Description":null,"MetaTitle":null,"MetaDescription":null,"Canonical":null,"VideoComments":[],"Subtitles":[],"ID":33709},{"Watched":false,"Name":"Concentration Cells and pH","Duration":"4m 27s","ChapterTopicVideoID":28669,"CourseChapterTopicPlaylistID":286842,"HasSubtitles":true,"ThumbnailPath":null,"UploadDate":null,"DurationForVideoObject":null,"Description":null,"MetaTitle":null,"MetaDescription":null,"Canonical":null,"VideoComments":[],"Subtitles":[{"Start":"00:00.000 ","End":"00:01.950","Text":"In the previous video,"},{"Start":"00:01.950 ","End":"00:03.870","Text":"we learnt about the Nernst equation."},{"Start":"00:03.870 ","End":"00:06.090","Text":"In this video, we\u0027ll apply the equation to"},{"Start":"00:06.090 ","End":"00:11.115","Text":"concentration cells and show how they can be used to measure pH."},{"Start":"00:11.115 ","End":"00:14.580","Text":"We\u0027re going to talk about concentration cells."},{"Start":"00:14.580 ","End":"00:17.940","Text":"A concentration cell consists of"},{"Start":"00:17.940 ","End":"00:24.075","Text":"2 half-cells with identical electrodes but different ion concentrations."},{"Start":"00:24.075 ","End":"00:30.125","Text":"Here\u0027s a picture. Since the electrodes are identical,"},{"Start":"00:30.125 ","End":"00:36.665","Text":"E standard cell is equal to 0 and E cell is equal to"},{"Start":"00:36.665 ","End":"00:44.435","Text":"E cell 0 minus 0.0257 volts divided by n ln Q."},{"Start":"00:44.435 ","End":"00:46.840","Text":"That\u0027s the Nernst equation."},{"Start":"00:46.840 ","End":"00:51.885","Text":"Because E cell 0 is 0,"},{"Start":"00:51.885 ","End":"01:01.165","Text":"then we get E cell is equal to minus 0.0257 volts divided by n ln Q."},{"Start":"01:01.165 ","End":"01:05.960","Text":"Although the cathode and anode are identical,"},{"Start":"01:05.960 ","End":"01:08.480","Text":"the 2 concentrations are different and we put"},{"Start":"01:08.480 ","End":"01:11.585","Text":"the higher concentration usually on the right."},{"Start":"01:11.585 ","End":"01:16.220","Text":"This is silver, silver plus half-cells."},{"Start":"01:16.220 ","End":"01:21.265","Text":"The more concentration solution is placed on the cathode side."},{"Start":"01:21.265 ","End":"01:26.150","Text":"Now we can relate the cell potential to the pH."},{"Start":"01:26.150 ","End":"01:33.005","Text":"We\u0027re going to have 2 identical half-cells on the left and the right."},{"Start":"01:33.005 ","End":"01:38.135","Text":"They both have platinum electrodes and they\u0027re both hydrogen electrodes,"},{"Start":"01:38.135 ","End":"01:40.100","Text":"but on the left-hand side,"},{"Start":"01:40.100 ","End":"01:44.715","Text":"the concentration is unknown, it\u0027s x molar."},{"Start":"01:44.715 ","End":"01:46.160","Text":"On the right-hand side,"},{"Start":"01:46.160 ","End":"01:48.800","Text":"this is a standard hydrogen electrode."},{"Start":"01:48.800 ","End":"01:51.925","Text":"The concentration is 1 molar."},{"Start":"01:51.925 ","End":"01:56.765","Text":"We have the standard hydrogen electrode on the right-hand side,"},{"Start":"01:56.765 ","End":"02:01.420","Text":"and a hydrogen electrode of unknown pH on the left-hand side."},{"Start":"02:01.420 ","End":"02:06.810","Text":"The anode H_2 gas goes to 2H plus in solution,"},{"Start":"02:06.810 ","End":"02:15.195","Text":"and the concentration is x and of course it\u0027s plus 2 electrons because this is oxidation."},{"Start":"02:15.195 ","End":"02:24.210","Text":"On the cathode side 2H plus concentration of 1 molar plus 2 electrons to give us H_2 gas."},{"Start":"02:24.210 ","End":"02:27.130","Text":"That\u0027s reduction."},{"Start":"02:27.230 ","End":"02:30.645","Text":"Overall, adding the 2 equations,"},{"Start":"02:30.645 ","End":"02:32.415","Text":"the 2 electrons goes,"},{"Start":"02:32.415 ","End":"02:38.400","Text":"we get 2H plus the concentration 1 molar on the left-hand side,"},{"Start":"02:38.400 ","End":"02:43.490","Text":"and 2H plus on the right-hand side with unknown concentration."},{"Start":"02:43.490 ","End":"02:45.665","Text":"We can write our equation,"},{"Start":"02:45.665 ","End":"02:50.530","Text":"E cell is equal to minus 0.0257 volts divided by"},{"Start":"02:50.530 ","End":"02:57.325","Text":"n ln Q as minus 0.0257 volts divided by 2,"},{"Start":"02:57.325 ","End":"02:59.990","Text":"because we have 2 electrons."},{"Start":"03:00.710 ","End":"03:04.965","Text":"ln x squared because we have 2H plus,"},{"Start":"03:04.965 ","End":"03:08.860","Text":"so we have ln x squared."},{"Start":"03:09.920 ","End":"03:17.590","Text":"ln x squared is equal to 2 ln x."},{"Start":"03:17.930 ","End":"03:23.680","Text":"We have 2 learn X here and we have a 2 here, so these cancel."},{"Start":"03:23.810 ","End":"03:29.205","Text":"We can write minus 0.0257 volts"},{"Start":"03:29.205 ","End":"03:37.535","Text":"ln x. ln x can be written in terms of log x."},{"Start":"03:37.535 ","End":"03:43.390","Text":"That\u0027s 2.303 log x."},{"Start":"03:43.390 ","End":"03:52.240","Text":"Here we have 0.0257 volts times 2.303 times minus log x."},{"Start":"03:52.240 ","End":"03:56.730","Text":"We can multiply these 2,"},{"Start":"03:56.730 ","End":"04:00.060","Text":"we get 0.059 volts."},{"Start":"04:00.060 ","End":"04:03.070","Text":"This of course is the pH,"},{"Start":"04:03.070 ","End":"04:08.495","Text":"because x is the concentration of H plus."},{"Start":"04:08.495 ","End":"04:16.530","Text":"Finally, we can write the E cell is equal to 0.059 volts times the pH."},{"Start":"04:16.720 ","End":"04:19.085","Text":"If we measure E cell,"},{"Start":"04:19.085 ","End":"04:20.945","Text":"we can find the pH."},{"Start":"04:20.945 ","End":"04:23.975","Text":"In this video we discussed concentration cells,"},{"Start":"04:23.975 ","End":"04:28.050","Text":"and how they have been used to measure the pH of a solution."}],"ID":33710},{"Watched":false,"Name":"Concentration Cells and Solubility Products","Duration":"3m 21s","ChapterTopicVideoID":28673,"CourseChapterTopicPlaylistID":286842,"HasSubtitles":true,"ThumbnailPath":null,"UploadDate":null,"DurationForVideoObject":null,"Description":null,"MetaTitle":null,"MetaDescription":null,"Canonical":null,"VideoComments":[],"Subtitles":[{"Start":"00:00.000 ","End":"00:02.115","Text":"In the previous video,"},{"Start":"00:02.115 ","End":"00:06.540","Text":"we learned about concentration cells and how to use them to measure pH."},{"Start":"00:06.540 ","End":"00:09.750","Text":"In this video, we use them to measure Ksp."},{"Start":"00:09.750 ","End":"00:14.505","Text":"We\u0027re going to measure the Ksp of silver iodide."},{"Start":"00:14.505 ","End":"00:17.490","Text":"Here\u0027s our cell, the same one as we had in"},{"Start":"00:17.490 ","End":"00:21.270","Text":"the previous video, just different concentrations."},{"Start":"00:21.270 ","End":"00:26.460","Text":"On the left-hand side of the silver, silver plus cell,"},{"Start":"00:26.460 ","End":"00:29.055","Text":"we have a saturated solution,"},{"Start":"00:29.055 ","End":"00:31.125","Text":"and on the right-hand side,"},{"Start":"00:31.125 ","End":"00:35.835","Text":"we have a concentration of 0.10 molar."},{"Start":"00:35.835 ","End":"00:41.620","Text":"It\u0027s x on the left-hand side and 0.10 on the right-hand side."},{"Start":"00:41.620 ","End":"00:43.850","Text":"When we measure the cell potential,"},{"Start":"00:43.850 ","End":"00:47.495","Text":"it\u0027s plus 0.417 volts."},{"Start":"00:47.495 ","End":"00:51.739","Text":"The anode we have silver going to silver plus,"},{"Start":"00:51.739 ","End":"00:54.980","Text":"plus an electron and on the cathode side,"},{"Start":"00:54.980 ","End":"00:56.480","Text":"we have silver plus,"},{"Start":"00:56.480 ","End":"00:58.760","Text":"plus electron going to silver."},{"Start":"00:58.760 ","End":"01:02.990","Text":"This is oxidation and this is reduction."},{"Start":"01:02.990 ","End":"01:12.010","Text":"Here we have the concentrations x on the anode and 0.10 on the cathode,"},{"Start":"01:12.010 ","End":"01:13.795","Text":"and when we add the 2,"},{"Start":"01:13.795 ","End":"01:16.130","Text":"the electron of course cancels."},{"Start":"01:16.130 ","End":"01:21.630","Text":"We get Ag plus with the concentration 0.10 molar on"},{"Start":"01:21.630 ","End":"01:27.605","Text":"the left-hand side going to Ag plus with concentration x on the right-hand side,"},{"Start":"01:27.605 ","End":"01:31.570","Text":"and we see the n is equal to 1 because there\u0027s only 1 electron involved."},{"Start":"01:31.570 ","End":"01:33.185","Text":"We can write that E cell,"},{"Start":"01:33.185 ","End":"01:36.965","Text":"which we know from measurement to 0.417,"},{"Start":"01:36.965 ","End":"01:46.765","Text":"is equal to minus 0.0257 volts divided by n lnQ and n is 1."},{"Start":"01:46.765 ","End":"01:51.950","Text":"We can work out that lnQ is equal to 0.417 divided by"},{"Start":"01:51.950 ","End":"02:00.300","Text":"0.0257 with a minus sign and that gives us lnQ equal to minus 16.2,"},{"Start":"02:00.300 ","End":"02:05.010","Text":"so Q is e to the power minus 16.2."},{"Start":"02:05.010 ","End":"02:08.955","Text":"That\u0027s 9.2 times 10 to the power of minus 8."},{"Start":"02:08.955 ","End":"02:12.200","Text":"Now we can write what Q is."},{"Start":"02:12.200 ","End":"02:16.385","Text":"Q is x because that\u0027s the concentration in right-hand side,"},{"Start":"02:16.385 ","End":"02:20.310","Text":"divided by 0.10, the concentration on the left-hand side,"},{"Start":"02:20.310 ","End":"02:26.755","Text":"so x divided by 0.10 is equal to 9.2 times 10 to the power of minus 8,"},{"Start":"02:26.755 ","End":"02:29.805","Text":"9.2 times 10 to the power minus 8."},{"Start":"02:29.805 ","End":"02:31.815","Text":"We can see what x is."},{"Start":"02:31.815 ","End":"02:39.040","Text":"x is just the multiplication of 0.10 times 9.21 times 10 to the power minus 8."},{"Start":"02:39.040 ","End":"02:43.905","Text":"X is 9.21 times 10 to the power minus 9."},{"Start":"02:43.905 ","End":"02:47.040","Text":"Now we can work out what Ksp is."},{"Start":"02:47.040 ","End":"02:53.570","Text":"Ksp is the concentration of Ag plus times the concentration of I minus,"},{"Start":"02:53.570 ","End":"02:58.290","Text":"and that\u0027s just x squared because for every Ag plus we get,"},{"Start":"02:58.290 ","End":"02:59.910","Text":"we get 1 I minus,"},{"Start":"02:59.910 ","End":"03:03.000","Text":"so that\u0027s x squared and we square this x,"},{"Start":"03:03.000 ","End":"03:06.990","Text":"we get 8.5 times 10 to the power minus 17."},{"Start":"03:06.990 ","End":"03:13.884","Text":"Ksp of AgI is 8.5 times 10 to the power minus 17."},{"Start":"03:13.884 ","End":"03:21.600","Text":"In this video, we used a concentration cell to calculate the solubility product of AgI."}],"ID":33711},{"Watched":false,"Name":"Ion-Selective Electrodes","Duration":"8m 50s","ChapterTopicVideoID":28672,"CourseChapterTopicPlaylistID":286842,"HasSubtitles":true,"ThumbnailPath":null,"UploadDate":null,"DurationForVideoObject":null,"Description":null,"MetaTitle":null,"MetaDescription":null,"Canonical":null,"VideoComments":[],"Subtitles":[{"Start":"00:00.000 ","End":"00:02.190","Text":"In a previous video,"},{"Start":"00:02.190 ","End":"00:07.215","Text":"we showed how to measure the pH using a concentration cell and in this video,"},{"Start":"00:07.215 ","End":"00:10.500","Text":"we\u0027ll talk about ion-selective electrodes,"},{"Start":"00:10.500 ","End":"00:14.850","Text":"and also more convenient ways to measure the pH."},{"Start":"00:14.850 ","End":"00:19.080","Text":"Let\u0027s start with ion-selective electrodes."},{"Start":"00:19.080 ","End":"00:23.250","Text":"An ion-selective electrode is an electrode that can be used to measure"},{"Start":"00:23.250 ","End":"00:27.975","Text":"the concentration of a particular ion in an aqueous solution."},{"Start":"00:27.975 ","End":"00:31.020","Text":"Examples are H^plus, Na^plus,"},{"Start":"00:31.020 ","End":"00:33.540","Text":"Ca^2 plus, NH4^plus,"},{"Start":"00:33.540 ","End":"00:36.000","Text":"CN^minus, S^2 minus."},{"Start":"00:36.000 ","End":"00:40.315","Text":"In this video, we\u0027ll concentrate on each plus."},{"Start":"00:40.315 ","End":"00:46.040","Text":"I\u0027m going to start by measuring the pH using a calomel electrode."},{"Start":"00:46.040 ","End":"00:51.935","Text":"We saw in a previous video that the pH can be measured using a concentration cell."},{"Start":"00:51.935 ","End":"00:53.930","Text":"It can also be measured using"},{"Start":"00:53.930 ","End":"01:00.245","Text":"a hydrogen electrode connected to a calomel electrode through a salt bridge."},{"Start":"01:00.245 ","End":"01:06.230","Text":"Calomel is a common name from mercury I chloride, that\u0027s Hg_2CO_2."},{"Start":"01:06.230 ","End":"01:12.799","Text":"The electrode consists of a piece of Hg_2CO_2 mixed with liquid mercury"},{"Start":"01:12.799 ","End":"01:19.415","Text":"in an inner tube and that is inserted in a solution of 1 molar KCl in an outer tube."},{"Start":"01:19.415 ","End":"01:24.030","Text":"The electrical connection is via a platinum wire."},{"Start":"01:24.610 ","End":"01:28.250","Text":"We have Hg_2CO_2,"},{"Start":"01:28.250 ","End":"01:31.625","Text":"liquid mercury as the electrode,"},{"Start":"01:31.625 ","End":"01:34.225","Text":"and 1 molar KCl."},{"Start":"01:34.225 ","End":"01:42.300","Text":"At the cathode, Hg_2CO_2 acquires 2 electrons and turns into 2 Hg,"},{"Start":"01:42.300 ","End":"01:44.520","Text":"that\u0027s liquid mercury,"},{"Start":"01:44.520 ","End":"01:52.680","Text":"plus 2 Cl minus and E^0 for that is plus 0.2680 volts."},{"Start":"01:52.680 ","End":"01:56.545","Text":"The anode is the hydrogen electrode,"},{"Start":"01:56.545 ","End":"02:04.645","Text":"H_2 gas at 1 bar that standard pressure to give 2 H^plus,"},{"Start":"02:04.645 ","End":"02:09.275","Text":"and here we have unknown concentration of H^plus,"},{"Start":"02:09.275 ","End":"02:13.370","Text":"so that\u0027s x molar plus 2 electrons."},{"Start":"02:13.370 ","End":"02:21.370","Text":"Now, the standard electrode potential for the hydrogen electrode we know to be 0."},{"Start":"02:21.370 ","End":"02:27.330","Text":"Overall we have Hg_2CO_2 plus H_2 to give 2 H^plus,"},{"Start":"02:27.330 ","End":"02:32.760","Text":"plus 2 Hg plus 2 Cl^minus and the E^0 cell for that"},{"Start":"02:32.760 ","End":"02:39.105","Text":"is equals 0.2680 volts because E^0 is 0,"},{"Start":"02:39.105 ","End":"02:44.860","Text":"so it\u0027s just the same as the electrode potential of the calomel cell."},{"Start":"02:44.860 ","End":"02:54.890","Text":"Now, we can use the Nernst equation to calculate the potential of this cell."},{"Start":"02:54.890 ","End":"02:59.975","Text":"If you recall, its E cell is equal to"},{"Start":"02:59.975 ","End":"03:09.280","Text":"E^0 cell minus RT divided by nF, ln Q."},{"Start":"03:09.280 ","End":"03:14.220","Text":"In this case, n is 2 because we have 2 electrons here."},{"Start":"03:14.220 ","End":"03:17.070","Text":"N is equal to 2."},{"Start":"03:17.070 ","End":"03:22.040","Text":"Here\u0027s the expression for Q. Q is equal to the concentration of"},{"Start":"03:22.040 ","End":"03:26.345","Text":"H^plus squared times the concentration of Cl minus squared."},{"Start":"03:26.345 ","End":"03:28.955","Text":"Now, why is that the volume of Q?"},{"Start":"03:28.955 ","End":"03:33.170","Text":"Because for Hg_2Cl_2 solid,"},{"Start":"03:33.170 ","End":"03:35.510","Text":"the activity is just 1."},{"Start":"03:35.510 ","End":"03:38.660","Text":"For H_2, which is standard pressure,"},{"Start":"03:38.660 ","End":"03:42.800","Text":"it\u0027s also 1 for Hg is a liquid,"},{"Start":"03:42.800 ","End":"03:46.655","Text":"so it\u0027s also 1 and we\u0027re left just with H^plus"},{"Start":"03:46.655 ","End":"03:51.340","Text":"and Cl^minus and they\u0027re squared because of this 2 and these 2."},{"Start":"03:51.340 ","End":"03:55.790","Text":"Q is equal to H^plus squared times Cl^minus squared."},{"Start":"03:55.790 ","End":"04:02.930","Text":"We can write that E_cell is equal to E^o_cell minus RT divided by 2F,"},{"Start":"04:02.930 ","End":"04:07.690","Text":"ln of H^plus squared times Cl^minus squared."},{"Start":"04:07.690 ","End":"04:12.010","Text":"Now we know that the ln of a product,"},{"Start":"04:12.010 ","End":"04:17.605","Text":"ln of ab is equal to ln of a plus ln of b."},{"Start":"04:17.605 ","End":"04:24.050","Text":"We can write this as E^0_cell minus RT over 2F ln of"},{"Start":"04:24.050 ","End":"04:30.305","Text":"Cl minus squared minus RT over 2F ln of H^plus squared."},{"Start":"04:30.305 ","End":"04:34.190","Text":"If we have the ln of something squared,"},{"Start":"04:34.190 ","End":"04:36.680","Text":"we know that ln x squared,"},{"Start":"04:36.680 ","End":"04:39.580","Text":"for example, is 2ln x."},{"Start":"04:39.580 ","End":"04:44.825","Text":"Now we can write this as 2ln Cl^minus,"},{"Start":"04:44.825 ","End":"04:48.260","Text":"and the 2 will then cancel with this 2 and we\u0027re left with"},{"Start":"04:48.260 ","End":"04:52.220","Text":"minus T divided by F ln Cl^minus."},{"Start":"04:52.220 ","End":"04:58.875","Text":"The same thing for the H^plus minus RT divided by F ln of H^plus."},{"Start":"04:58.875 ","End":"05:08.450","Text":"Now, if we take these two as a constant called E_O^c, c for calomel,"},{"Start":"05:08.450 ","End":"05:13.715","Text":"we get that this is E^c_0"},{"Start":"05:13.715 ","End":"05:21.455","Text":"minus RT divided by F times 2.3 or 3."},{"Start":"05:21.455 ","End":"05:24.610","Text":"The turns are ln to a log,"},{"Start":"05:24.610 ","End":"05:32.540","Text":"has a volume of 0.0592 volts at 25 degrees Celsius."},{"Start":"05:32.540 ","End":"05:35.914","Text":"We\u0027ve met that in previous videos."},{"Start":"05:35.914 ","End":"05:44.420","Text":"Now we have E_0^c minus 0.0592 volts times the log of H^plus."},{"Start":"05:44.420 ","End":"05:48.830","Text":"We know that minus the log of H^plus is a pH."},{"Start":"05:48.830 ","End":"05:59.885","Text":"We can write that E_cell is equal to E_0^c plus 0.0592 volts times the pH."},{"Start":"05:59.885 ","End":"06:05.735","Text":"We can calibrate the cell by measuring the cell potential for known pH."},{"Start":"06:05.735 ","End":"06:09.515","Text":"Then we can plot the E_cell versus the pH,"},{"Start":"06:09.515 ","End":"06:20.140","Text":"and that gives us a straight line and the intercept is E_cell^0 or rather E_0^c."},{"Start":"06:20.170 ","End":"06:25.820","Text":"What\u0027s the saturated calomel electrode that\u0027s called SCE?"},{"Start":"06:25.820 ","End":"06:30.890","Text":"Now if the KCl in the calomel electrode is saturated,"},{"Start":"06:30.890 ","End":"06:34.550","Text":"it\u0027s called the saturated calomel electrode and it\u0027s often used as"},{"Start":"06:34.550 ","End":"06:39.065","Text":"the standard electrode potential 0.2412 volts."},{"Start":"06:39.065 ","End":"06:43.430","Text":"It\u0027s a very accurate put standard."},{"Start":"06:43.430 ","End":"06:46.940","Text":"We\u0027re going to talk a little about the glass electrode."},{"Start":"06:46.940 ","End":"06:52.820","Text":"A glass electrode is much easier to use than a hydrogen electrode."},{"Start":"06:52.820 ","End":"06:56.660","Text":"It consists of a thin-walled porous glass bulb at"},{"Start":"06:56.660 ","End":"07:00.650","Text":"the end of a tube containing an Ag-AgCl electrode,"},{"Start":"07:00.650 ","End":"07:05.570","Text":"and an HCl solution of known concentration."},{"Start":"07:05.570 ","End":"07:10.520","Text":"Here\u0027s a picture, here\u0027s the Ag-AgCl electrode"},{"Start":"07:10.520 ","End":"07:19.195","Text":"here and the HCl solution of known concentration, usually 1 molar."},{"Start":"07:19.195 ","End":"07:24.755","Text":"Here\u0027s our thin-walled porous glass bulb."},{"Start":"07:24.755 ","End":"07:28.595","Text":"Now when the bulb is placed in the solution of unknown pH,"},{"Start":"07:28.595 ","End":"07:31.535","Text":"a potential develops across the membrane."},{"Start":"07:31.535 ","End":"07:35.315","Text":"This membrane, just as in a concentration cell."},{"Start":"07:35.315 ","End":"07:37.580","Text":"To measure the potential difference,"},{"Start":"07:37.580 ","End":"07:40.130","Text":"we can use a reference cell such as"},{"Start":"07:40.130 ","End":"07:46.580","Text":"a saturated calomel electrode that we\u0027ve met before or yet another Ag-AgCl electrode,"},{"Start":"07:46.580 ","End":"07:51.095","Text":"and that\u0027s connected to the glass electrode by a salt bridge."},{"Start":"07:51.095 ","End":"07:56.090","Text":"Now if we use the Ag-AgCl electrode as the reference,"},{"Start":"07:56.090 ","End":"07:59.554","Text":"and of course, that is also in the glass electrode."},{"Start":"07:59.554 ","End":"08:04.790","Text":"Then E_cell^0 will just be"},{"Start":"08:04.790 ","End":"08:11.975","Text":"0 because we have the same electrode in both anode and cathode."},{"Start":"08:11.975 ","End":"08:19.520","Text":"E_cell we can show is 0.0592 volts times the pH."},{"Start":"08:19.520 ","End":"08:24.425","Text":"We can have a meter that converts E_cell to the pH."},{"Start":"08:24.425 ","End":"08:29.510","Text":"Now modern pH meters have both electrodes and the salt bridge in 1 probe."},{"Start":"08:29.510 ","End":"08:31.370","Text":"Here\u0027s the probe, here."},{"Start":"08:31.370 ","End":"08:36.830","Text":"You can see the bulb of the glass lecture peeping out."},{"Start":"08:36.830 ","End":"08:39.095","Text":"Here on the screen,"},{"Start":"08:39.095 ","End":"08:43.210","Text":"we get the pH and also the temperature."},{"Start":"08:43.210 ","End":"08:50.669","Text":"In this video, we talked about ion-selective electrodes and methods of measuring the pH."}],"ID":33712}],"Thumbnail":null,"ID":286842},{"Name":"Electrolytic Cells","TopicPlaylistFirstVideoID":0,"Duration":null,"Videos":[{"Watched":false,"Name":"Electrolytic Cells 1","Duration":"5m 41s","ChapterTopicVideoID":28665,"CourseChapterTopicPlaylistID":286843,"HasSubtitles":true,"ThumbnailPath":null,"UploadDate":null,"DurationForVideoObject":null,"Description":null,"MetaTitle":null,"MetaDescription":null,"Canonical":null,"VideoComments":[],"Subtitles":[{"Start":"00:00.000 ","End":"00:04.425","Text":"In previous videos we learned about galvanic or voltaic cells."},{"Start":"00:04.425 ","End":"00:06.000","Text":"In this video and the next,"},{"Start":"00:06.000 ","End":"00:08.950","Text":"we\u0027ll learn about electrolytic cells."},{"Start":"00:09.440 ","End":"00:13.845","Text":"What did we learn about galvanic or voltaic cells?"},{"Start":"00:13.845 ","End":"00:18.945","Text":"We learned that they generate electrical energy from a chemical reaction."},{"Start":"00:18.945 ","End":"00:23.250","Text":"The overall chemical reaction is spontaneous."},{"Start":"00:23.250 ","End":"00:26.115","Text":"Now, what\u0027s electrolysis?"},{"Start":"00:26.115 ","End":"00:31.860","Text":"Electrolysis is a process of driving a reaction in the non-spontaneous direction,"},{"Start":"00:31.860 ","End":"00:36.290","Text":"the opposite direction, using an electric current."},{"Start":"00:36.290 ","End":"00:39.370","Text":"What\u0027s an electrolytic cell?"},{"Start":"00:39.370 ","End":"00:44.255","Text":"That\u0027s an electrochemical cell in which electrolysis takes place."},{"Start":"00:44.255 ","End":"00:46.460","Text":"It\u0027s called electrolytic cell."},{"Start":"00:46.460 ","End":"00:48.680","Text":"Now, very often, but not always,"},{"Start":"00:48.680 ","End":"00:51.880","Text":"the 2 electrodes share the same container."},{"Start":"00:51.880 ","End":"00:54.625","Text":"Then there\u0027s only 1 electrolyte."},{"Start":"00:54.625 ","End":"00:58.825","Text":"The concentrations in pressures are not always standard."},{"Start":"00:58.825 ","End":"01:00.889","Text":"Lets consider the example,"},{"Start":"01:00.889 ","End":"01:06.529","Text":"the electrolysis of natch above 801 degrees Celsius."},{"Start":"01:06.529 ","End":"01:09.320","Text":"That\u0027s called molten NaCL."},{"Start":"01:09.320 ","End":"01:12.430","Text":"The process is called the Downs process."},{"Start":"01:12.430 ","End":"01:18.025","Text":"It\u0027s a method of preparing sodium and chlorine gas."},{"Start":"01:18.025 ","End":"01:20.715","Text":"Here\u0027s an illustration."},{"Start":"01:20.715 ","End":"01:24.355","Text":"Here\u0027s our anode and cathode,"},{"Start":"01:24.355 ","End":"01:27.379","Text":"and here\u0027s the battery."},{"Start":"01:27.379 ","End":"01:30.640","Text":"We\u0027ll see that the cathode, in this case,"},{"Start":"01:30.640 ","End":"01:36.450","Text":"is negative and the anode is positive."},{"Start":"01:37.580 ","End":"01:42.209","Text":"The electrons come out of this battery,"},{"Start":"01:42.209 ","End":"01:45.999","Text":"and are pushed along here to the cathode."},{"Start":"01:45.999 ","End":"01:51.740","Text":"Then the ions carry the current along to the anode,"},{"Start":"01:51.740 ","End":"01:58.375","Text":"which is positive, and then the electrons are pushed along this far."},{"Start":"01:58.375 ","End":"02:02.055","Text":"Now, oxidation takes place at the anode,"},{"Start":"02:02.055 ","End":"02:04.205","Text":"and reduction at the cathode."},{"Start":"02:04.205 ","End":"02:09.320","Text":"In this respect, this is the same as the voltaic cell."},{"Start":"02:09.320 ","End":"02:11.545","Text":"That\u0027s the meaning of this plus."},{"Start":"02:11.545 ","End":"02:13.995","Text":"If I write across,"},{"Start":"02:13.995 ","End":"02:17.960","Text":"that means that it\u0027s different from the voltaic cell."},{"Start":"02:17.960 ","End":"02:23.450","Text":"The anode, 2Cl minus goes to chlorine gas plus 2 electrons."},{"Start":"02:23.450 ","End":"02:25.640","Text":"That\u0027s an oxidation process."},{"Start":"02:25.640 ","End":"02:29.790","Text":"E^0 is minus 1.36 volts."},{"Start":"02:31.280 ","End":"02:35.370","Text":"At the cathode, 2Na plus,"},{"Start":"02:35.370 ","End":"02:38.670","Text":"plus 2 electrons gives us 2Na."},{"Start":"02:38.670 ","End":"02:40.800","Text":"That\u0027s a reduction process."},{"Start":"02:40.800 ","End":"02:45.160","Text":"E^0 is minus 2.71 volts."},{"Start":"02:46.430 ","End":"02:49.590","Text":"When we add the 2,"},{"Start":"02:49.590 ","End":"02:52.275","Text":"the 2 electrons cancels,"},{"Start":"02:52.275 ","End":"02:54.360","Text":"we get 2Na plus,"},{"Start":"02:54.360 ","End":"02:59.520","Text":"plus 2Cl minus, giving us 2Na plus Cl_2."},{"Start":"02:59.520 ","End":"03:02.145","Text":"That Cl_2, of course, is a gas."},{"Start":"03:02.145 ","End":"03:11.040","Text":"Then we take the sum of these 2 E^0s and we get E^0 for the cell is minus 4.07 volts."},{"Start":"03:11.040 ","End":"03:17.540","Text":"That\u0027s negative, which means we\u0027re talking about a non-spontaneous process."},{"Start":"03:17.540 ","End":"03:25.025","Text":"Just a remark, it\u0027s important to separate the Na from Cl_2 so they do not react."},{"Start":"03:25.025 ","End":"03:28.100","Text":"In contrast to voltaic cell,"},{"Start":"03:28.100 ","End":"03:31.445","Text":"current must be supplied for the reaction to occur."},{"Start":"03:31.445 ","End":"03:33.995","Text":"The current supplied by the battery,"},{"Start":"03:33.995 ","End":"03:36.965","Text":"a battery is a galvanic cell in this case,"},{"Start":"03:36.965 ","End":"03:39.395","Text":"which pushes electrons along the wire,"},{"Start":"03:39.395 ","End":"03:41.690","Text":"forcing oxidation at the anode,"},{"Start":"03:41.690 ","End":"03:44.430","Text":"and reduction at the cathode."},{"Start":"03:45.680 ","End":"03:48.610","Text":"Now, in order for the reaction to occur,"},{"Start":"03:48.610 ","End":"03:52.060","Text":"the battery must supply more than 4 volts."},{"Start":"03:52.060 ","End":"03:55.585","Text":"Here we have minus 4.07 volts."},{"Start":"03:55.585 ","End":"03:58.750","Text":"In order to overcome this negative potential,"},{"Start":"03:58.750 ","End":"04:02.240","Text":"we have to supply more than 4 volts."},{"Start":"04:02.240 ","End":"04:06.750","Text":"Now, distinction from the galvanic cell,"},{"Start":"04:06.750 ","End":"04:10.630","Text":"the anode here is positive and the cathode is negative."},{"Start":"04:10.630 ","End":"04:13.675","Text":"Remember, for a voltaic cell,"},{"Start":"04:13.675 ","End":"04:14.890","Text":"the anode is negative,"},{"Start":"04:14.890 ","End":"04:17.150","Text":"the cathode is positive."},{"Start":"04:20.390 ","End":"04:23.970","Text":"But similar to the voltaic cell,"},{"Start":"04:23.970 ","End":"04:27.730","Text":"the electrons travel through the wire from the anode to the cathode."},{"Start":"04:27.730 ","End":"04:33.830","Text":"Now, anions in"},{"Start":"04:33.830 ","End":"04:38.885","Text":"the electrolyte move towards the anode and cations move towards the cathode."},{"Start":"04:38.885 ","End":"04:44.130","Text":"You can see the an, cat, cot."},{"Start":"04:46.610 ","End":"04:49.740","Text":"Here, we can see it in the picture,"},{"Start":"04:49.740 ","End":"04:52.800","Text":"Na plus cations moving to the cathode,"},{"Start":"04:52.800 ","End":"04:55.830","Text":"Cl minus anions moving into the anode."},{"Start":"04:55.830 ","End":"04:57.825","Text":"Now, in a galvanic cell,"},{"Start":"04:57.825 ","End":"04:59.300","Text":"this is also the case,"},{"Start":"04:59.300 ","End":"05:01.940","Text":"but it\u0027s the anions in the salt bridge that go to"},{"Start":"05:01.940 ","End":"05:06.305","Text":"the anode and the cations in the salt bridge that go to the cathode."},{"Start":"05:06.305 ","End":"05:10.945","Text":"Now, what to do about electrode charges because this is a confusing subject."},{"Start":"05:10.945 ","End":"05:12.240","Text":"In a galvanic cell,"},{"Start":"05:12.240 ","End":"05:15.065","Text":"the electrons are generated at the anode,"},{"Start":"05:15.065 ","End":"05:16.685","Text":"so it\u0027s negative,"},{"Start":"05:16.685 ","End":"05:18.440","Text":"and consumed at the cathode,"},{"Start":"05:18.440 ","End":"05:20.425","Text":"so it\u0027s considered positive."},{"Start":"05:20.425 ","End":"05:24.240","Text":"In an electrolytic cell,"},{"Start":"05:24.240 ","End":"05:28.385","Text":"an external power source supplies electrons to the cathode,"},{"Start":"05:28.385 ","End":"05:29.765","Text":"so it\u0027s negative,"},{"Start":"05:29.765 ","End":"05:33.080","Text":"and removes them from the anode, so it\u0027s positive."},{"Start":"05:33.080 ","End":"05:35.420","Text":"In this video, we learned about"},{"Start":"05:35.420 ","End":"05:40.650","Text":"electrolytic cells and we\u0027ll continue the discussion in the next video."}],"ID":30198},{"Watched":false,"Name":"Electrolytic Cells 2","Duration":"7m 57s","ChapterTopicVideoID":28666,"CourseChapterTopicPlaylistID":286843,"HasSubtitles":true,"ThumbnailPath":null,"UploadDate":null,"DurationForVideoObject":null,"Description":null,"MetaTitle":null,"MetaDescription":null,"Canonical":null,"VideoComments":[],"Subtitles":[{"Start":"00:00.000 ","End":"00:02.160","Text":"In the previous video,"},{"Start":"00:02.160 ","End":"00:04.605","Text":"we learned about electrolytic cells."},{"Start":"00:04.605 ","End":"00:08.010","Text":"In this video, we\u0027ll continue the discussion."},{"Start":"00:08.010 ","End":"00:12.600","Text":"Now there are a few complicating issues when we"},{"Start":"00:12.600 ","End":"00:17.955","Text":"discuss electrolytic cells and the first one is the overpotential."},{"Start":"00:17.955 ","End":"00:22.679","Text":"In order to drive a reaction in the non-spontaneous direction,"},{"Start":"00:22.679 ","End":"00:27.330","Text":"the potential difference supplied by the power source must be greater and"},{"Start":"00:27.330 ","End":"00:32.910","Text":"often much greater than the potential difference for the spontaneous reaction."},{"Start":"00:32.910 ","End":"00:37.860","Text":"This extra potential is called the overpotential."},{"Start":"00:37.860 ","End":"00:39.600","Text":"Let\u0027s take an example,"},{"Start":"00:39.600 ","End":"00:42.010","Text":"the electrolysis of water."},{"Start":"00:42.010 ","End":"00:44.805","Text":"Here\u0027s a spontaneous reaction,"},{"Start":"00:44.805 ","End":"00:51.720","Text":"2 moles of hydrogen gas plus 1 mole of oxygen gas to give us 2 moles of liquid water."},{"Start":"00:51.730 ","End":"01:00.035","Text":"The E cell for that is +1.23 volts at pH=7."},{"Start":"01:00.035 ","End":"01:03.709","Text":"Now for the non-spontaneous reaction,"},{"Start":"01:03.709 ","End":"01:06.380","Text":"which write the equation the other way round,"},{"Start":"01:06.380 ","End":"01:13.175","Text":"2 moles of water to give us 2 moles of hydrogen and 1 mole of oxygen."},{"Start":"01:13.175 ","End":"01:16.445","Text":"Then E cell has the opposite sign."},{"Start":"01:16.445 ","End":"01:21.795","Text":"It\u0027s minus 1.23 volts at pH=7."},{"Start":"01:21.795 ","End":"01:26.000","Text":"You would think that we needed to supply 1.23"},{"Start":"01:26.000 ","End":"01:31.850","Text":"volts in order to overcome this negative E cell."},{"Start":"01:31.850 ","End":"01:35.690","Text":"Now, when we perform the experiment,"},{"Start":"01:35.690 ","End":"01:37.910","Text":"we see that for platinum electrodes,"},{"Start":"01:37.910 ","End":"01:43.135","Text":"the potential required to drive the reaction is 1.8 volts,"},{"Start":"01:43.135 ","End":"01:46.370","Text":"so overpotential is 0.6 volts."},{"Start":"01:46.370 ","End":"01:53.640","Text":"We thought we needed to supply 1.2 volts and in fact we need 1.8 volts."},{"Start":"01:55.430 ","End":"02:01.114","Text":"This is our overpotential is 0.6 volts."},{"Start":"02:01.114 ","End":"02:06.640","Text":"Just to remark that oxygen is produced at the anode and hydrogen at the cathode."},{"Start":"02:06.640 ","End":"02:09.675","Text":"Now, when we want to electrolyze water,"},{"Start":"02:09.675 ","End":"02:11.680","Text":"an electrolyte is usually added."},{"Start":"02:11.680 ","End":"02:19.045","Text":"That\u0027s because water itself has low conductivity because it has so few ions."},{"Start":"02:19.045 ","End":"02:25.315","Text":"Usually you add sodium sulfate since neither iron reacts during electrolysis,"},{"Start":"02:25.315 ","End":"02:31.555","Text":"neither the sodium plus nor the sulfate reacts, SO_4_2 minus."},{"Start":"02:31.555 ","End":"02:36.345","Text":"Another issue is that there are competing electrode reactions."},{"Start":"02:36.345 ","End":"02:40.970","Text":"Let\u0027s consider the electrolysis of salt solution."},{"Start":"02:40.970 ","End":"02:45.050","Text":"Now, when we talked about molten sodium chloride,"},{"Start":"02:45.050 ","End":"02:50.935","Text":"there was only one possible oxidation and one possible reduction process."},{"Start":"02:50.935 ","End":"02:55.535","Text":"However, in the electrolysis of NaCl in aqueous solution,"},{"Start":"02:55.535 ","End":"03:01.105","Text":"there are two possible oxidation and two possible reduction processes."},{"Start":"03:01.105 ","End":"03:05.295","Text":"The first reduction process is 2Na+,"},{"Start":"03:05.295 ","End":"03:13.770","Text":"plus 2 electrons to give us Na and E^0 for that is -2.71 volts."},{"Start":"03:13.770 ","End":"03:20.915","Text":"Another reduction process is 2 moles of water reacting with 2 electrons to give us"},{"Start":"03:20.915 ","End":"03:27.470","Text":"H_2 gas and 2OH minus ions, that\u0027s hydroxide."},{"Start":"03:27.470 ","End":"03:32.530","Text":"E^0 for that is -0.83 volts."},{"Start":"03:32.530 ","End":"03:36.289","Text":"There are two possible oxidation processes."},{"Start":"03:36.289 ","End":"03:41.240","Text":"2Cl minus, to give us chlorine gas and 2 electrons."},{"Start":"03:41.240 ","End":"03:47.960","Text":"E^0 for that is -1.36 volts and also 2 moles"},{"Start":"03:47.960 ","End":"03:54.665","Text":"of water to give us oxygen gas plus 4 moles of H plus, plus 4 electrons."},{"Start":"03:54.665 ","End":"03:59.050","Text":"E^0 for that is -1.23 volts."},{"Start":"03:59.050 ","End":"04:01.990","Text":"Now the first reduction process doesn\u0027t"},{"Start":"04:01.990 ","End":"04:06.250","Text":"occur because it\u0027s very negative compared to the others."},{"Start":"04:06.250 ","End":"04:09.950","Text":"This is out, this doesn\u0027t occur."},{"Start":"04:10.230 ","End":"04:14.245","Text":"We don\u0027t get sodium produced."},{"Start":"04:14.245 ","End":"04:18.170","Text":"There are two possible combinations."},{"Start":"04:18.170 ","End":"04:21.360","Text":"First combination we\u0027ll call A,"},{"Start":"04:21.360 ","End":"04:26.470","Text":"is 2 water molecules plus 2 electrons to give us hydrogen plus"},{"Start":"04:26.470 ","End":"04:36.730","Text":"2 moles of hydroxide and that\u0027s E^0 equal to -0.83 volts."},{"Start":"04:36.730 ","End":"04:38.940","Text":"That of course is reduction."},{"Start":"04:38.940 ","End":"04:41.865","Text":"Then we have oxidation,"},{"Start":"04:41.865 ","End":"04:47.265","Text":"2Cl- ions going to CO_2 plus 2 electrons."},{"Start":"04:47.265 ","End":"04:51.480","Text":"E^0 for that is -1.36 volts."},{"Start":"04:51.480 ","End":"04:54.825","Text":"Overall we have 2 moles of water,"},{"Start":"04:54.825 ","End":"05:00.940","Text":"plus 2 moles of Cl- to give us H_2 gas plus chlorine gas,"},{"Start":"05:00.940 ","End":"05:05.370","Text":"Cl_2 gas plus 2 moles of OH minus."},{"Start":"05:05.370 ","End":"05:12.310","Text":"We add this up, we get E cell equal to -2.19 volts."},{"Start":"05:12.310 ","End":"05:14.620","Text":"That\u0027s one process."},{"Start":"05:14.620 ","End":"05:18.265","Text":"A second possibility, we\u0027ll call that B,"},{"Start":"05:18.265 ","End":"05:26.823","Text":"is 4 moles of water plus 4 electrons to give us 2 moles of hydrogen plus 4 of OH-,"},{"Start":"05:26.823 ","End":"05:31.025","Text":"and E^0 for that is -0.83 volts."},{"Start":"05:31.025 ","End":"05:32.420","Text":"It\u0027s the same as we had before,"},{"Start":"05:32.420 ","End":"05:37.340","Text":"except we\u0027ve multiplied by 2 in order to add properly."},{"Start":"05:37.340 ","End":"05:41.375","Text":"The second process, which is oxidation,"},{"Start":"05:41.375 ","End":"05:45.110","Text":"this is reduction, of course, this oxidation."},{"Start":"05:45.110 ","End":"05:53.045","Text":"2 moles of water to give us 1 mole of oxygen gas plus 4H+ plus 4 electrons."},{"Start":"05:53.045 ","End":"06:00.330","Text":"That\u0027s E^0 equal to -1.23 volts so that when we add the two,"},{"Start":"06:00.330 ","End":"06:04.875","Text":"we get 6H_2O here 4 and 2,"},{"Start":"06:04.875 ","End":"06:10.620","Text":"to give us 2H_2 plus oxygen 2 plus 4H+,"},{"Start":"06:10.620 ","End":"06:11.955","Text":"that\u0027s from here,"},{"Start":"06:11.955 ","End":"06:14.435","Text":"and 4OH- from here."},{"Start":"06:14.435 ","End":"06:19.880","Text":"But of course, H+ and OH- together give us water."},{"Start":"06:19.880 ","End":"06:22.910","Text":"We have 4 water molecules here,"},{"Start":"06:22.910 ","End":"06:29.190","Text":"4 moles of water and here we have 6 so we\u0027re left with just 2."},{"Start":"06:29.190 ","End":"06:33.840","Text":"2 moles of water to give us 2 hydrogen 2,"},{"Start":"06:33.840 ","End":"06:37.195","Text":"plus 1 oxygen 2."},{"Start":"06:37.195 ","End":"06:39.470","Text":"When we add these two up,"},{"Start":"06:39.470 ","End":"06:43.295","Text":"we get -2.06 volts."},{"Start":"06:43.295 ","End":"06:45.755","Text":"The two doubles are very similar."},{"Start":"06:45.755 ","End":"06:51.140","Text":"Here we have -2.19 and here -2.06."},{"Start":"06:51.140 ","End":"06:56.165","Text":"The cell potentials are similar but there is an overpotential."},{"Start":"06:56.165 ","End":"07:00.580","Text":"The overpotential for B is much greater than for A."},{"Start":"07:00.580 ","End":"07:07.085","Text":"What happens is A because the overall potential for B is much greater."},{"Start":"07:07.085 ","End":"07:11.030","Text":"A is what happens and we get chlorine at"},{"Start":"07:11.030 ","End":"07:16.340","Text":"the inert anode and hydrogen and NaOH at the cathode."},{"Start":"07:16.340 ","End":"07:19.580","Text":"I\u0027ve emphasized that we needed an inert anode,"},{"Start":"07:19.580 ","End":"07:22.480","Text":"so it\u0027s not to react with the chlorine 2."},{"Start":"07:22.480 ","End":"07:24.385","Text":"Now, a few words,"},{"Start":"07:24.385 ","End":"07:29.990","Text":"B relates to the cell potential for the electrolysis of water under standard conditions."},{"Start":"07:29.990 ","End":"07:38.450","Text":"That\u0027s a concentration of H+=1 M at the anode and OH- =1 M at the cathode."},{"Start":"07:38.450 ","End":"07:41.945","Text":"But if we\u0027re talking about pure water with pH 7,"},{"Start":"07:41.945 ","End":"07:46.465","Text":"E cell is -1.23 volts."},{"Start":"07:46.465 ","End":"07:51.830","Text":"Here when pH is 7, it\u0027s nonstandard conditions."},{"Start":"07:51.830 ","End":"07:57.090","Text":"In this video and the previous one we learned about electrolytic cells."}],"ID":30199}],"Thumbnail":null,"ID":286843},{"Name":"Electrolysis","TopicPlaylistFirstVideoID":0,"Duration":null,"Videos":[{"Watched":false,"Name":"Products of Electrolysis","Duration":"5m 4s","ChapterTopicVideoID":28668,"CourseChapterTopicPlaylistID":286844,"HasSubtitles":true,"ThumbnailPath":null,"UploadDate":null,"DurationForVideoObject":null,"Description":null,"MetaTitle":null,"MetaDescription":null,"Canonical":null,"VideoComments":[],"Subtitles":[{"Start":"00:00.000 ","End":"00:01.665","Text":"In the previous videos,"},{"Start":"00:01.665 ","End":"00:05.445","Text":"we talked about electrolysis and electrolytic cells."},{"Start":"00:05.445 ","End":"00:07.560","Text":"In this video, we\u0027ll calculate"},{"Start":"00:07.560 ","End":"00:12.480","Text":"the maximum amount of product that can be formed by electrolysis."},{"Start":"00:12.480 ","End":"00:16.710","Text":"Let\u0027s talk about Faraday\u0027s law of electrolysis."},{"Start":"00:16.710 ","End":"00:21.899","Text":"This says that the amount of product formed or reactant consumed"},{"Start":"00:21.899 ","End":"00:27.195","Text":"by an electric current is equivalent to the moles of electrons supplied."},{"Start":"00:27.195 ","End":"00:29.130","Text":"Let\u0027s take an example."},{"Start":"00:29.130 ","End":"00:33.239","Text":"Let\u0027s consider refining copper in an electrolytic cell,"},{"Start":"00:33.239 ","End":"00:35.405","Text":"that\u0027s called electro refining."},{"Start":"00:35.405 ","End":"00:38.555","Text":"Now the anode, which we know is positive,"},{"Start":"00:38.555 ","End":"00:42.890","Text":"consists of impure copper and the cathode,"},{"Start":"00:42.890 ","End":"00:45.020","Text":"which we know as minus,"},{"Start":"00:45.020 ","End":"00:46.925","Text":"consists of pure copper."},{"Start":"00:46.925 ","End":"00:51.335","Text":"We have impure copper here and pure copper here."},{"Start":"00:51.335 ","End":"00:55.380","Text":"Here\u0027s our battery, positive and negative."},{"Start":"00:55.380 ","End":"01:01.505","Text":"The electrolyte is copper sulfate solution and often sulfuric acid is added to it."},{"Start":"01:01.505 ","End":"01:05.080","Text":"Here\u0027s our copper sulfate solution, nice blue color."},{"Start":"01:05.080 ","End":"01:10.905","Text":"This is carried out in low voltage so the impurities are not oxidized."},{"Start":"01:10.905 ","End":"01:12.560","Text":"This is impure copper,"},{"Start":"01:12.560 ","End":"01:14.930","Text":"so there are lots of impurities."},{"Start":"01:14.930 ","End":"01:17.435","Text":"Now at the anode,"},{"Start":"01:17.435 ","End":"01:19.190","Text":"the copper is oxidized,"},{"Start":"01:19.190 ","End":"01:22.910","Text":"so we get copper going to CU^2 plus, plus 2 electrons."},{"Start":"01:22.910 ","End":"01:28.310","Text":"Then these CU^2 plus ions migrate to the cathode,"},{"Start":"01:28.310 ","End":"01:31.119","Text":"where the reduced pure copper."},{"Start":"01:31.119 ","End":"01:33.690","Text":"We have at the cathode, CU^2 plus,"},{"Start":"01:33.690 ","End":"01:37.350","Text":"plus 2 electrons to give us copper."},{"Start":"01:37.350 ","End":"01:41.839","Text":"The CU^2 plus ions are going in this direction."},{"Start":"01:41.839 ","End":"01:44.480","Text":"Now, as we can see from the equation,"},{"Start":"01:44.480 ","End":"01:48.975","Text":"we need 2 moles of electrons to produce 1 mole of copper."},{"Start":"01:48.975 ","End":"01:51.110","Text":"We can write that as this equation."},{"Start":"01:51.110 ","End":"01:58.100","Text":"Number of moles of electrons divided by the number of moles of copper is equal to 2."},{"Start":"01:58.100 ","End":"02:01.105","Text":"This is important ratio that we need to use,"},{"Start":"02:01.105 ","End":"02:04.595","Text":"and the impurities dropped to the bottom of the beaker."},{"Start":"02:04.595 ","End":"02:10.519","Text":"How many moles of electrons are supplied by our power source?"},{"Start":"02:10.519 ","End":"02:18.620","Text":"Now Q, the quantity of electricity passed through the cell in coulombs is equal to I,"},{"Start":"02:18.620 ","End":"02:22.130","Text":"the current in amperes,"},{"Start":"02:22.130 ","End":"02:25.535","Text":"times t, the time in seconds."},{"Start":"02:25.535 ","End":"02:29.705","Text":"Q is the quantity of electricity passed through the cell in coulombs,"},{"Start":"02:29.705 ","End":"02:31.730","Text":"I is the current in amperes,"},{"Start":"02:31.730 ","End":"02:34.730","Text":"and we know the amperes is equal to coulombs per second,"},{"Start":"02:34.730 ","End":"02:37.930","Text":"and t is the time the current flows in second."},{"Start":"02:37.930 ","End":"02:41.030","Text":"Now we also know that Q is equal to n,"},{"Start":"02:41.030 ","End":"02:43.880","Text":"the number of moles of electrons times F,"},{"Start":"02:43.880 ","End":"02:46.750","Text":"where F is Faraday\u0027s constant."},{"Start":"02:46.750 ","End":"02:53.490","Text":"Remember that F is equal to 9.6485 times 10^4 coulombs per mole."},{"Start":"02:53.490 ","End":"02:56.500","Text":"We can equate these, It=nF,"},{"Start":"02:57.920 ","End":"03:02.154","Text":"so nF=It, that means n,"},{"Start":"03:02.154 ","End":"03:06.325","Text":"the number of moles of electrons is equals to It/F."},{"Start":"03:06.325 ","End":"03:08.525","Text":"Here\u0027s an example."},{"Start":"03:08.525 ","End":"03:16.655","Text":"What mass of copper can be deposited on the cathode in 1 hour by current of 1.5 amperes?"},{"Start":"03:16.655 ","End":"03:21.250","Text":"Now the number of moles of electrons is It/F."},{"Start":"03:21.250 ","End":"03:25.170","Text":"That\u0027s 1.5 coulombs per second,"},{"Start":"03:25.170 ","End":"03:27.000","Text":"that\u0027s the same as amperes,"},{"Start":"03:27.000 ","End":"03:29.520","Text":"times 3,600 seconds,"},{"Start":"03:29.520 ","End":"03:32.460","Text":"that\u0027s 1 hour divided by F,"},{"Start":"03:32.460 ","End":"03:37.765","Text":"F is 9.6485 times 10^4 Coulombs per mole."},{"Start":"03:37.765 ","End":"03:39.020","Text":"If we work that out,"},{"Start":"03:39.020 ","End":"03:43.200","Text":"we get 0.0560 moles."},{"Start":"03:44.200 ","End":"03:50.780","Text":"Seconds of power minus 1 goes with seconds and coulombs goes with coulombs."},{"Start":"03:50.780 ","End":"03:56.930","Text":"We\u0027re left just with mol^-1, 1/mol^-1 is moles."},{"Start":"03:56.930 ","End":"04:01.840","Text":"That\u0027s the number of moles of electrons we require,"},{"Start":"04:01.840 ","End":"04:05.645","Text":"0.0560 moles of electrons."},{"Start":"04:05.645 ","End":"04:09.710","Text":"Now the number of moles of copper is the number of moles of"},{"Start":"04:09.710 ","End":"04:14.285","Text":"copper divided by the number of moles of electrons times the number moles of electrons."},{"Start":"04:14.285 ","End":"04:19.490","Text":"We already saw that this ratio is 1/2."},{"Start":"04:19.490 ","End":"04:24.065","Text":"The number of moles of electrons is 0.0560,"},{"Start":"04:24.065 ","End":"04:28.910","Text":"multiply that out, 0.0280 moles."},{"Start":"04:28.910 ","End":"04:31.385","Text":"This is moles of copper."},{"Start":"04:31.385 ","End":"04:33.995","Text":"Now we can work out the mass of copper,"},{"Start":"04:33.995 ","End":"04:40.415","Text":"that 0.0280 moles of copper multiplied by the molar mass,"},{"Start":"04:40.415 ","End":"04:42.901","Text":"63.5 grams per mole."},{"Start":"04:42.901 ","End":"04:44.330","Text":"When we multiply that out,"},{"Start":"04:44.330 ","End":"04:47.515","Text":"we get 1.78 grams."},{"Start":"04:47.515 ","End":"04:51.440","Text":"The mass of copper that is deposited at the cathode in 1 hour by"},{"Start":"04:51.440 ","End":"04:56.975","Text":"current of 1.5 amperes is 1.78 grams."},{"Start":"04:56.975 ","End":"05:00.170","Text":"In this video, we calculated the maximum amount of"},{"Start":"05:00.170 ","End":"05:03.900","Text":"product that can be formed by electrolysis."}],"ID":30200},{"Watched":false,"Name":"Applications of Electrolysis","Duration":"3m 6s","ChapterTopicVideoID":28667,"CourseChapterTopicPlaylistID":286844,"HasSubtitles":true,"ThumbnailPath":null,"UploadDate":null,"DurationForVideoObject":null,"Description":null,"MetaTitle":null,"MetaDescription":null,"Canonical":null,"VideoComments":[],"Subtitles":[{"Start":"00:00.000 ","End":"00:02.010","Text":"In the previous videos,"},{"Start":"00:02.010 ","End":"00:03.925","Text":"we learned about electrolysis."},{"Start":"00:03.925 ","End":"00:08.595","Text":"In this video, we\u0027ll talk about some applications of electrolysis."},{"Start":"00:08.595 ","End":"00:12.480","Text":"We talked about some applications in previous videos."},{"Start":"00:12.480 ","End":"00:14.655","Text":"A few remarks,"},{"Start":"00:14.655 ","End":"00:20.609","Text":"we used inert electrodes and the cell is designed to keep the sodium chlorine separate,"},{"Start":"00:20.609 ","End":"00:22.275","Text":"and away from water."},{"Start":"00:22.275 ","End":"00:27.930","Text":"We can add calcium chloride to reduce the melting point of NaCl."},{"Start":"00:27.930 ","End":"00:31.800","Text":"That\u0027s in the video, Electrolytic cells 1."},{"Start":"00:33.560 ","End":"00:36.930","Text":"Then in Electrolytic cells 2,"},{"Start":"00:36.930 ","End":"00:40.310","Text":"we talked about the chlor-alkali industrial process."},{"Start":"00:40.310 ","End":"00:45.035","Text":"That\u0027s an industrial production of chlorine gas, hydrogen gas,"},{"Start":"00:45.035 ","End":"00:53.890","Text":"and sodium hydroxide in aqueous form by electrolysis of concentrated NaCl solution."},{"Start":"00:53.890 ","End":"00:57.145","Text":"We also talked about electrorefining,"},{"Start":"00:57.145 ","End":"01:00.305","Text":"that\u0027s refining copper in electrolytic cell,"},{"Start":"01:00.305 ","End":"01:03.470","Text":"and that was in the video, Products of electrolysis."},{"Start":"01:03.470 ","End":"01:05.750","Text":"Here are a few more applications."},{"Start":"01:05.750 ","End":"01:12.395","Text":"First of all, the production of pure magnesium and aluminum."},{"Start":"01:12.395 ","End":"01:16.130","Text":"In a similar way to production of pure sodium,"},{"Start":"01:16.130 ","End":"01:18.950","Text":"pure magnesium metal can be produced from"},{"Start":"01:18.950 ","End":"01:24.875","Text":"molten magnesium chloride and pure aluminum metal can be produced from alumina,"},{"Start":"01:24.875 ","End":"01:33.345","Text":"that\u0027s Al_2O_3, and that\u0027s mixed with molten cryolite, Na_3AlF_6."},{"Start":"01:33.345 ","End":"01:36.165","Text":"There\u0027s also electroplating."},{"Start":"01:36.165 ","End":"01:40.760","Text":"Electroplating is electrolytic deposition of a thin film of"},{"Start":"01:40.760 ","End":"01:45.845","Text":"metal on an object to improve its appearance or protect it from corrosion."},{"Start":"01:45.845 ","End":"01:51.200","Text":"For example, the electroplating of nickel onto steel."},{"Start":"01:51.200 ","End":"01:57.425","Text":"We have an anode made of nickel metal and a cathode of steel."},{"Start":"01:57.425 ","End":"02:03.920","Text":"We insert these electrodes in nickel sulfate."},{"Start":"02:03.920 ","End":"02:06.830","Text":"When an external voltage is applied,"},{"Start":"02:06.830 ","End":"02:12.935","Text":"the oxidation of nickel occurs at the anode and reduction occurs at the cathode."},{"Start":"02:12.935 ","End":"02:15.170","Text":"Here\u0027s that reduction process,"},{"Start":"02:15.170 ","End":"02:18.775","Text":"Ni_2 plus, plus 2 electrons to give us nickel."},{"Start":"02:18.775 ","End":"02:24.399","Text":"E^0 for that is minus 0.28 volts."},{"Start":"02:24.470 ","End":"02:32.150","Text":"At the cathode, steel cathode is coated with a thin layer of nickel."},{"Start":"02:32.150 ","End":"02:38.524","Text":"Now, since both the anode and cathode have the same reaction occurring,"},{"Start":"02:38.524 ","End":"02:41.660","Text":"the cell potential is 0."},{"Start":"02:41.660 ","End":"02:47.945","Text":"We only require a very small potential to transfer nickel from anode to cathode."},{"Start":"02:47.945 ","End":"02:53.280","Text":"In this video, we discussed some applications of electrolysis."}],"ID":30201}],"Thumbnail":null,"ID":286844},{"Name":"Corrosion","TopicPlaylistFirstVideoID":0,"Duration":null,"Videos":[{"Watched":false,"Name":"Corrosion","Duration":"8m 3s","ChapterTopicVideoID":28674,"CourseChapterTopicPlaylistID":286845,"HasSubtitles":true,"ThumbnailPath":null,"UploadDate":null,"DurationForVideoObject":null,"Description":null,"MetaTitle":null,"MetaDescription":null,"Canonical":null,"VideoComments":[],"Subtitles":[{"Start":"00:00.750 ","End":"00:03.100","Text":"In the previous videos,"},{"Start":"00:03.100 ","End":"00:06.070","Text":"we talked about electrolysis and its uses."},{"Start":"00:06.070 ","End":"00:09.560","Text":"In this video we\u0027ll talk about corrosion."},{"Start":"00:10.500 ","End":"00:13.960","Text":"We\u0027re going to talk about corrosion."},{"Start":"00:13.960 ","End":"00:19.230","Text":"Corrosion is the undesired oxidation of metals."},{"Start":"00:19.230 ","End":"00:26.705","Text":"It\u0027s an electrochemical process related to the process occurring in Galvanic cells."},{"Start":"00:26.705 ","End":"00:30.610","Text":"Now, the electrochemical series that we learnt in"},{"Start":"00:30.610 ","End":"00:34.810","Text":"the previous video can help to explain this process."},{"Start":"00:34.810 ","End":"00:39.730","Text":"We need to recall that the more negative the standard electrode potential,"},{"Start":"00:39.730 ","End":"00:45.435","Text":"the greater the strength of the reduced form as a reducing agent."},{"Start":"00:45.435 ","End":"00:52.695","Text":"Let\u0027s first talk about the rusting of iron in water with no air, no oxygen."},{"Start":"00:52.695 ","End":"01:00.675","Text":"2 water molecules reacts with 2 electrons to give us H_2 gas and 2OH minus,"},{"Start":"01:00.675 ","End":"01:06.220","Text":"and E^0 for this is minus 0.83 volts."},{"Start":"01:06.220 ","End":"01:09.499","Text":"Now, this is a standard electrode potential"},{"Start":"01:09.499 ","End":"01:13.840","Text":"because the concentration of OH minus is 1 molar."},{"Start":"01:13.840 ","End":"01:16.795","Text":"But if we have pH 7,"},{"Start":"01:16.795 ","End":"01:20.300","Text":"these are no longer standard conditions, then E,"},{"Start":"01:20.300 ","End":"01:21.455","Text":"the electric potential,"},{"Start":"01:21.455 ","End":"01:24.925","Text":"is minus 0.42 volts."},{"Start":"01:24.925 ","End":"01:30.200","Text":"Any metal with standard electrode potential more negative than minus"},{"Start":"01:30.200 ","End":"01:36.215","Text":"0.42 volts can reduce water and undergo oxidation."},{"Start":"01:36.215 ","End":"01:38.720","Text":"Let\u0027s look at iron."},{"Start":"01:38.720 ","End":"01:42.180","Text":"Fe^2 plus, plus 2 electrons gives us Fe,"},{"Start":"01:42.180 ","End":"01:44.190","Text":"that\u0027s a reduction process,"},{"Start":"01:44.190 ","End":"01:49.950","Text":"and E^0 for this is minus 0.44 volts."},{"Start":"01:49.950 ","End":"01:58.140","Text":"It\u0027s very, very similar to the E for water at pH 7."},{"Start":"01:58.140 ","End":"02:02.705","Text":"The standard electrode potential of iron is similar to that of water,"},{"Start":"02:02.705 ","End":"02:07.975","Text":"pH 7, so the iron does not rust in water in the absence of oxygen."},{"Start":"02:07.975 ","End":"02:10.200","Text":"You can try this at home,"},{"Start":"02:10.200 ","End":"02:14.284","Text":"take something made of iron and put it in water,"},{"Start":"02:14.284 ","End":"02:19.250","Text":"excluding the oxygen, and it will just stay there without rusting."},{"Start":"02:19.250 ","End":"02:21.829","Text":"However, usually we do have oxygen,"},{"Start":"02:21.829 ","End":"02:26.410","Text":"so what about the rusting of iron in damp air?"},{"Start":"02:26.410 ","End":"02:30.310","Text":"That\u0027s air containing water and oxygen."},{"Start":"02:30.310 ","End":"02:34.570","Text":"We need to take into account this process,"},{"Start":"02:34.570 ","End":"02:37.453","Text":"O_2, oxygen, plus 4H,"},{"Start":"02:37.453 ","End":"02:47.184","Text":"plus 4 electrons to give us 2H_20 and the E^0 for that is plus 1.23 volts."},{"Start":"02:47.184 ","End":"02:50.870","Text":"Now, this is a standard electrode potential when"},{"Start":"02:50.870 ","End":"02:54.575","Text":"the concentration of H plus is 1 molar,"},{"Start":"02:54.575 ","End":"02:56.525","Text":"1 mole per liter."},{"Start":"02:56.525 ","End":"02:58.470","Text":"But if we have pH 7,"},{"Start":"02:58.470 ","End":"03:00.230","Text":"as we usually do in water,"},{"Start":"03:00.230 ","End":"03:06.815","Text":"and the partial pressure of O_2 is 0.2 bars,"},{"Start":"03:06.815 ","End":"03:11.585","Text":"then E is plus 0.81 volts."},{"Start":"03:11.585 ","End":"03:17.435","Text":"That sits lower than the standard electrode potential."},{"Start":"03:17.435 ","End":"03:20.910","Text":"Now, the electrode potential is higher,"},{"Start":"03:20.910 ","End":"03:24.135","Text":"plus 0.81, than that for iron."},{"Start":"03:24.135 ","End":"03:27.330","Text":"Remember, iron was minus 0.44."},{"Start":"03:27.330 ","End":"03:32.290","Text":"Iron can reduce the oxygen and become oxidized."},{"Start":"03:32.290 ","End":"03:36.190","Text":"Iron is oxidized."},{"Start":"03:37.910 ","End":"03:42.259","Text":"Iron is oxidized in the presence of oxygen and water."},{"Start":"03:42.259 ","End":"03:45.945","Text":"After it\u0027s oxidized to Fe^2 plus,"},{"Start":"03:45.945 ","End":"03:49.750","Text":"Fe^2 plus can then be oxidized to Fe^3 plus."},{"Start":"03:49.750 ","End":"03:53.325","Text":"Here\u0027s the electrode potential, Fe^3 plus,"},{"Start":"03:53.325 ","End":"03:55.560","Text":"plus electrode to Fe^2 plus,"},{"Start":"03:55.560 ","End":"04:01.440","Text":"and E^0 for that is plus 0.77 volts."},{"Start":"04:01.440 ","End":"04:08.375","Text":"Now, let\u0027s consider the rusting of iron as a series of steps."},{"Start":"04:08.375 ","End":"04:11.885","Text":"Let\u0027s consider the very first oxidation step."},{"Start":"04:11.885 ","End":"04:16.370","Text":"Here we have the water droplet on iron, this is iron,"},{"Start":"04:16.370 ","End":"04:18.380","Text":"this is water,"},{"Start":"04:18.380 ","End":"04:23.725","Text":"and there\u0027s oxygen near air."},{"Start":"04:23.725 ","End":"04:27.110","Text":"The water has oxygen in it near the air boundary,"},{"Start":"04:27.110 ","End":"04:30.020","Text":"the boundary between the iron and the air."},{"Start":"04:30.020 ","End":"04:33.665","Text":"Now, this is like a very small Galvanic cell."},{"Start":"04:33.665 ","End":"04:39.740","Text":"The water droplet is the electrolyte of iron near the center of the drop here,"},{"Start":"04:39.740 ","End":"04:41.795","Text":"where there\u0027s less oxygen here,"},{"Start":"04:41.795 ","End":"04:48.990","Text":"it\u0027s the anode and where there is oxygen is the cathode, near here."},{"Start":"04:48.990 ","End":"04:52.020","Text":"The anode, 2 moles of"},{"Start":"04:52.020 ","End":"05:00.030","Text":"iron is oxidized to 2 moles of Fe^2 plus, plus 4 electrons."},{"Start":"05:00.030 ","End":"05:02.975","Text":"That\u0027s oxidation. At the cathode,"},{"Start":"05:02.975 ","End":"05:05.390","Text":"oxygen reacts with 4 H plus,"},{"Start":"05:05.390 ","End":"05:08.360","Text":"plus 4 electrons to give us 2H_2O."},{"Start":"05:08.360 ","End":"05:10.310","Text":"That\u0027s reduction process."},{"Start":"05:10.310 ","End":"05:14.730","Text":"Overall, cross electrons, cancels."},{"Start":"05:14.730 ","End":"05:22.545","Text":"We have 2Fe plus O_2 plus 4 H plus to give us 2Fe^2 plus,"},{"Start":"05:22.545 ","End":"05:25.860","Text":"plus 2H_2O, and we\u0027re going to call that A."},{"Start":"05:25.860 ","End":"05:30.830","Text":"Now, the electrons move from the anode to the cathode and"},{"Start":"05:30.830 ","End":"05:36.965","Text":"then they\u0027re replenished from the metal underneath the oxygen-poor part of the water."},{"Start":"05:36.965 ","End":"05:43.810","Text":"This is the oxygen-poor part of the water and that produces Fe^2 plus."},{"Start":"05:43.810 ","End":"05:50.815","Text":"Now, these ions dissolve in the water drop and that leaves small pits in the metal."},{"Start":"05:50.815 ","End":"05:55.395","Text":"Our metal is breaking up at small pits in it."},{"Start":"05:55.395 ","End":"05:58.965","Text":"Now, we have the 2nd oxidation process."},{"Start":"05:58.965 ","End":"06:05.835","Text":"In that one, Fe(II) is oxidized to Fe(III) by the dissolved oxygen."},{"Start":"06:05.835 ","End":"06:11.430","Text":"The anode, we have 2Fe^2 plus going to 2Fe^3 plus,"},{"Start":"06:11.430 ","End":"06:16.590","Text":"plus 2 electrons, that\u0027s our oxidation."},{"Start":"06:16.590 ","End":"06:20.460","Text":"At the cathode, 1/2 O_2 plus 2 H plus,"},{"Start":"06:20.460 ","End":"06:24.045","Text":"plus 2 electrons, giving us water, that\u0027s reduction."},{"Start":"06:24.045 ","End":"06:26.490","Text":"Overall when we add it up,"},{"Start":"06:26.490 ","End":"06:27.690","Text":"it goes with 2 electrons,"},{"Start":"06:27.690 ","End":"06:29.190","Text":"goes with 2 electrons."},{"Start":"06:29.190 ","End":"06:31.260","Text":"We get 2Fe^2 plus,"},{"Start":"06:31.260 ","End":"06:37.665","Text":"plus half O2 plus 2H plus to give us 2Fe^3 plus, plus water."},{"Start":"06:37.665 ","End":"06:40.095","Text":"We\u0027re going to call that B."},{"Start":"06:40.095 ","End":"06:47.865","Text":"Now, these irons precipitate as Fe_2O_3.H_2O, that\u0027s brown rust."},{"Start":"06:47.865 ","End":"06:49.670","Text":"How does that happen?"},{"Start":"06:49.670 ","End":"06:52.930","Text":"The oxygen ions come from the water,"},{"Start":"06:52.930 ","End":"07:01.185","Text":"4H_2O plus 2Fe^3 plus to give us 6H plus, plus Fe_2O_3.H_20."},{"Start":"07:01.185 ","End":"07:06.270","Text":"We\u0027re going to call that Process C. We have Process A, B,"},{"Start":"07:06.270 ","End":"07:11.625","Text":"and C. The removal of the rust drives the reaction to the right,"},{"Start":"07:11.625 ","End":"07:17.600","Text":"so the rust is precipitating and the reaction goes to the right."},{"Start":"07:17.600 ","End":"07:20.825","Text":"Now, we have 6H plus ions here,"},{"Start":"07:20.825 ","End":"07:26.760","Text":"and 6H plus ions participate in the 1st and 2nd oxidations,"},{"Start":"07:26.760 ","End":"07:29.310","Text":"2 in the 1st and 4 in the 2nd,"},{"Start":"07:29.310 ","End":"07:31.290","Text":"and so it\u0027s like a catalyst."},{"Start":"07:31.290 ","End":"07:34.835","Text":"6H plus gets recycled all the time."},{"Start":"07:34.835 ","End":"07:37.635","Text":"Now, if we add up A, B, and C,"},{"Start":"07:37.635 ","End":"07:43.874","Text":"we get iron plus 3 halves oxygen 2 plus water,"},{"Start":"07:43.874 ","End":"07:48.840","Text":"giving us Fe_20_3.H_20 and that\u0027s our rust."},{"Start":"07:48.840 ","End":"07:53.045","Text":"Now, if we add salt to the water as happens near the sea,"},{"Start":"07:53.045 ","End":"07:58.580","Text":"that makes the water more conductive and leads to even more rust."},{"Start":"07:58.580 ","End":"08:03.240","Text":"In this video, we talked about the corrosion of iron."}],"ID":30202},{"Watched":false,"Name":"Preventing Corrosion","Duration":"3m 32s","ChapterTopicVideoID":28675,"CourseChapterTopicPlaylistID":286845,"HasSubtitles":true,"ThumbnailPath":null,"UploadDate":null,"DurationForVideoObject":null,"Description":null,"MetaTitle":null,"MetaDescription":null,"Canonical":null,"VideoComments":[],"Subtitles":[{"Start":"00:00.000 ","End":"00:01.680","Text":"In the previous video,"},{"Start":"00:01.680 ","End":"00:03.149","Text":"we talked about corrosion,"},{"Start":"00:03.149 ","End":"00:07.320","Text":"and this video will discuss methods of preventing corrosion."},{"Start":"00:07.320 ","End":"00:11.070","Text":"We\u0027re going to talk about preventing corrosion."},{"Start":"00:11.070 ","End":"00:15.960","Text":"Now, we learned to corrosion is an electrochemical process."},{"Start":"00:15.960 ","End":"00:20.775","Text":"We can use electrochemical processes to counteract it."},{"Start":"00:20.775 ","End":"00:24.030","Text":"Now, obviously the simplest process is to paint"},{"Start":"00:24.030 ","End":"00:28.005","Text":"the surface of metal to prevent contact with air and water."},{"Start":"00:28.005 ","End":"00:30.465","Text":"However, if the paint flakes off,"},{"Start":"00:30.465 ","End":"00:35.445","Text":"the iron is exposed and corrosion will occur, rusting will occur."},{"Start":"00:35.445 ","End":"00:38.955","Text":"Better method is to galvanize the iron."},{"Start":"00:38.955 ","End":"00:41.210","Text":"The iron could be galvanize,"},{"Start":"00:41.210 ","End":"00:44.615","Text":"that means coated with a thin layer of zinc."},{"Start":"00:44.615 ","End":"00:49.115","Text":"Zinc has a more negative electrode potential than iron."},{"Start":"00:49.115 ","End":"00:51.530","Text":"The electrode potential for iron,"},{"Start":"00:51.530 ","End":"01:00.320","Text":"iron 2 plus plus 2 electrons to give iron is E^0 = to minus 0.44 volts."},{"Start":"01:00.320 ","End":"01:02.960","Text":"The electrode potential for zinc,"},{"Start":"01:02.960 ","End":"01:10.415","Text":"zinc 2 plus plus 2 electrons to give zinc is minus 0.76 volts."},{"Start":"01:10.415 ","End":"01:13.925","Text":"It\u0027s more negative than that of iron."},{"Start":"01:13.925 ","End":"01:21.635","Text":"Zinc is a stronger reducing agent than iron and is more readily oxidized than iron."},{"Start":"01:21.635 ","End":"01:24.740","Text":"Even if the zinc coating is broken,"},{"Start":"01:24.740 ","End":"01:28.430","Text":"zinc will be oxidized rather than iron."},{"Start":"01:28.430 ","End":"01:32.120","Text":"Zinc also corrodes, but it corrodes much slower than"},{"Start":"01:32.120 ","End":"01:36.005","Text":"iron and develops a protective layer of zinc oxide,"},{"Start":"01:36.005 ","End":"01:41.540","Text":"which is later converted to zinc hydroxide when exposed to water in the atmosphere."},{"Start":"01:41.540 ","End":"01:43.355","Text":"Now if it\u0027s left a long time,"},{"Start":"01:43.355 ","End":"01:46.850","Text":"many other minerals and crystalline substances develop"},{"Start":"01:46.850 ","End":"01:50.720","Text":"on the zinc after exposure to the environment."},{"Start":"01:50.720 ","End":"01:56.965","Text":"Examples of zinc, carbonate and Zn_5 carbonate, OH_6."},{"Start":"01:56.965 ","End":"02:02.525","Text":"This is a mixture of zinc carbonate and zinc hydroxide."},{"Start":"02:02.525 ","End":"02:06.380","Text":"Now, often after the industrial coating of iron and with zinc,"},{"Start":"02:06.380 ","End":"02:10.010","Text":"we further process to form the zinc layer is"},{"Start":"02:10.010 ","End":"02:16.325","Text":"passivated and accrual be absolution to enhance its resistance to corrosion."},{"Start":"02:16.325 ","End":"02:19.055","Text":"This is called passivation."},{"Start":"02:19.055 ","End":"02:23.930","Text":"Another method used for large objects is cathodic protection."},{"Start":"02:23.930 ","End":"02:27.650","Text":"Cathodic protection is the electrochemical protection of"},{"Start":"02:27.650 ","End":"02:32.450","Text":"a metal object by connecting it to more strongly reducing metal."},{"Start":"02:32.450 ","End":"02:36.260","Text":"For example, if we want to protect an iron or steel pipeline,"},{"Start":"02:36.260 ","End":"02:41.930","Text":"it can be connected to blocks of magnesium or zinc buried in the earth."},{"Start":"02:41.930 ","End":"02:45.040","Text":"Here\u0027s our pipeline buried in the earth,"},{"Start":"02:45.040 ","End":"02:50.375","Text":"and here\u0027s our block of magnesium or zinc, and they\u0027re connected."},{"Start":"02:50.375 ","End":"02:54.515","Text":"Here\u0027s moist Earth that can act as an electrolyte."},{"Start":"02:54.515 ","End":"03:01.565","Text":"The pipeline is the cathode and the magnesium or zinc is a sacrificial anode,"},{"Start":"03:01.565 ","End":"03:04.310","Text":"and it supplies electrodes to the cathode here,"},{"Start":"03:04.310 ","End":"03:06.710","Text":"the electrons going from left to right,"},{"Start":"03:06.710 ","End":"03:08.825","Text":"going from the anode to the cathode."},{"Start":"03:08.825 ","End":"03:15.245","Text":"That prevents oxidation of the pipeline."},{"Start":"03:15.245 ","End":"03:21.300","Text":"But the anode is sacrificed to save the cathode."},{"Start":"03:21.300 ","End":"03:24.555","Text":"It disintegrates gradually,"},{"Start":"03:24.555 ","End":"03:27.480","Text":"and must be replaced periodically."},{"Start":"03:27.480 ","End":"03:31.740","Text":"In this video, we learnt how to prevent corrosion."}],"ID":30203}],"Thumbnail":null,"ID":286845},{"Name":"Batteries","TopicPlaylistFirstVideoID":0,"Duration":null,"Videos":[{"Watched":false,"Name":"Primary Cells","Duration":"5m 41s","ChapterTopicVideoID":28763,"CourseChapterTopicPlaylistID":292351,"HasSubtitles":true,"ThumbnailPath":null,"UploadDate":null,"DurationForVideoObject":null,"Description":null,"MetaTitle":null,"MetaDescription":null,"Canonical":null,"VideoComments":[],"Subtitles":[{"Start":"00:00.000 ","End":"00:02.370","Text":"In the previous videos,"},{"Start":"00:02.370 ","End":"00:04.940","Text":"we learned about electrochemical cells."},{"Start":"00:04.940 ","End":"00:06.870","Text":"Then, the next two videos we\u0027ll talk about"},{"Start":"00:06.870 ","End":"00:10.545","Text":"primary and secondary cells used in batteries."},{"Start":"00:10.545 ","End":"00:13.245","Text":"What\u0027s an electrical battery?"},{"Start":"00:13.245 ","End":"00:19.620","Text":"A battery is a device that stores chemical energy for later release as electrical energy."},{"Start":"00:19.620 ","End":"00:24.675","Text":"It can consist of one or more electrochemical cells."},{"Start":"00:24.675 ","End":"00:29.265","Text":"Battery should be safe, environmentally friendly,"},{"Start":"00:29.265 ","End":"00:34.335","Text":"portable, and inexpensive with a stable potential and a long life."},{"Start":"00:34.335 ","End":"00:38.010","Text":"Useful definition is the specific energy."},{"Start":"00:38.010 ","End":"00:44.300","Text":"The specific energy of a cell is the energy generated divided by the mass."},{"Start":"00:44.300 ","End":"00:49.120","Text":"The units are kilowatt-hours divided by kilograms."},{"Start":"00:49.120 ","End":"00:53.095","Text":"Obviously, we want the specific energy to be high."},{"Start":"00:53.095 ","End":"00:55.790","Text":"What\u0027s a primary cell?"},{"Start":"00:55.790 ","End":"01:01.474","Text":"A primary cell is a galvanic cell with the reactants sealed inside a container."},{"Start":"01:01.474 ","End":"01:08.090","Text":"It cannot be recharged and discarded hopefully safely when the reactants are used up."},{"Start":"01:08.090 ","End":"01:10.610","Text":"On the other hand, there\u0027s a secondary cell."},{"Start":"01:10.610 ","End":"01:13.115","Text":"We\u0027ll talk about that in the next video."},{"Start":"01:13.115 ","End":"01:18.800","Text":"A secondary cell can be recharged many times by passing electricity through the cell."},{"Start":"01:18.800 ","End":"01:22.400","Text":"It acts as a galvanic cell while discharging."},{"Start":"01:22.400 ","End":"01:26.795","Text":"Discharging is when it converts chemical energy to electrical energy."},{"Start":"01:26.795 ","End":"01:30.515","Text":"As electrolytic cell while being charged."},{"Start":"01:30.515 ","End":"01:34.475","Text":"That\u0027s when you convert electrical energy to chemical energy."},{"Start":"01:34.475 ","End":"01:37.495","Text":"Let\u0027s discuss a few primary cells."},{"Start":"01:37.495 ","End":"01:42.650","Text":"The oldest primary cell is probably the dry cell."},{"Start":"01:42.650 ","End":"01:45.215","Text":"That\u0027s based on the Leclanche cell,"},{"Start":"01:45.215 ","End":"01:48.980","Text":"which was patented in 1866."},{"Start":"01:48.980 ","End":"01:54.700","Text":"Here\u0027s a picture you\u0027re probably very familiar with these sorts of batteries."},{"Start":"01:54.700 ","End":"01:58.205","Text":"Dry cells are used in computer mice,"},{"Start":"01:58.205 ","End":"02:01.460","Text":"torches, remote controls, etc."},{"Start":"02:01.460 ","End":"02:05.170","Text":"The cylindrical zinc container is the anode."},{"Start":"02:05.170 ","End":"02:09.460","Text":"This is the anode. The carbon rod,"},{"Start":"02:09.460 ","End":"02:13.150","Text":"usually made of graphite in the center surrounded by"},{"Start":"02:13.150 ","End":"02:17.725","Text":"manganese oxide and carbon black is the cathode."},{"Start":"02:17.725 ","End":"02:19.990","Text":"This is a cathode."},{"Start":"02:19.990 ","End":"02:23.050","Text":"First, Anode is negative,"},{"Start":"02:23.050 ","End":"02:25.690","Text":"and the cathode is positive."},{"Start":"02:25.690 ","End":"02:31.820","Text":"The zinc container is lined with some fabric to form a porous barrier."},{"Start":"02:31.940 ","End":"02:36.670","Text":"The electrolyte is a moist paste of ammonium chloride,"},{"Start":"02:36.670 ","End":"02:40.600","Text":"NH_4Cl, zinc chloride, and starch."},{"Start":"02:40.600 ","End":"02:48.610","Text":"Disadvantages, the zinc reacts with ammonium to form zinc (NH_3)4^2 plus."},{"Start":"02:49.400 ","End":"02:56.060","Text":"The cell potential is 1.5 V. That\u0027s independent of the size of the battery."},{"Start":"02:56.060 ","End":"02:57.695","Text":"We can have A batteries,"},{"Start":"02:57.695 ","End":"02:59.660","Text":"AA batteries, AAA,"},{"Start":"02:59.660 ","End":"03:01.430","Text":"and all other batteries,"},{"Start":"03:01.430 ","End":"03:06.605","Text":"but they\u0027re all 1.5 V. Since the 1970s,"},{"Start":"03:06.605 ","End":"03:10.805","Text":"the alkaline battery has largely replaced the dry cell."},{"Start":"03:10.805 ","End":"03:14.100","Text":"It\u0027s more stable and has a long shelf life."},{"Start":"03:14.100 ","End":"03:17.090","Text":"It has no voltage drop, and it\u0027s reliable."},{"Start":"03:17.090 ","End":"03:19.734","Text":"Its performance is very reliable."},{"Start":"03:19.734 ","End":"03:24.330","Text":"It\u0027s similar to the dry cell apart from the electrolyte."},{"Start":"03:24.330 ","End":"03:28.550","Text":"The electrolyte is basic NaOH or KOH."},{"Start":"03:28.550 ","End":"03:31.055","Text":"Another word for basic is alkaline."},{"Start":"03:31.055 ","End":"03:33.010","Text":"That\u0027s how it got its name."},{"Start":"03:33.010 ","End":"03:39.400","Text":"NaOH or KOH don\u0027t react with zinc when the battery isn\u0027t in use."},{"Start":"03:39.400 ","End":"03:43.505","Text":"At the anode, zinc reacts with 2 moles of"},{"Start":"03:43.505 ","End":"03:48.605","Text":"OH minus to give us ZnO plus water plus 2 electrons."},{"Start":"03:48.605 ","End":"03:51.115","Text":"That of course it\u0027s oxidation."},{"Start":"03:51.115 ","End":"03:56.960","Text":"At the cathode, manganese oxide reacts with 2 moles of"},{"Start":"03:56.960 ","End":"04:03.625","Text":"water plus 2 electrons to give us manganese hydroxide and 2 moles of OH minus."},{"Start":"04:03.625 ","End":"04:06.495","Text":"That of course is reduction."},{"Start":"04:06.495 ","End":"04:15.920","Text":"Once again, the cell potential is 1.5 V. Another primary battery is a silver oxide cell."},{"Start":"04:15.920 ","End":"04:20.000","Text":"This is a more expensive cell but has a very stable voltage,"},{"Start":"04:20.000 ","End":"04:25.120","Text":"1.55 V. It\u0027s used for pacemakers and hearing aids."},{"Start":"04:25.120 ","End":"04:31.970","Text":"The silver oxide cell is a primary cell with silver oxide in graphite as the cathode,"},{"Start":"04:31.970 ","End":"04:39.765","Text":"zinc anode, and KOH potassium hydroxide gel as electrolyte."},{"Start":"04:39.765 ","End":"04:47.895","Text":"At the anode, zinc reacts with 2OH minus to give us ZnO plus water plus 2 electrons."},{"Start":"04:47.895 ","End":"04:50.205","Text":"That of course is oxidation."},{"Start":"04:50.205 ","End":"04:56.000","Text":"At the cathode, silver oxide reacts with water plus 2 electrons to give us"},{"Start":"04:56.000 ","End":"05:02.675","Text":"2 moles of metal silver plus 2 moles of hydroxide."},{"Start":"05:02.675 ","End":"05:09.950","Text":"Well, that\u0027s reduction. The battery can be made very small as a button or coin battery."},{"Start":"05:09.950 ","End":"05:13.445","Text":"Here\u0027s our button or coin battery."},{"Start":"05:13.445 ","End":"05:15.415","Text":"Let\u0027s look at the bottom one."},{"Start":"05:15.415 ","End":"05:18.440","Text":"We have a steel anode cap,"},{"Start":"05:18.440 ","End":"05:21.985","Text":"Zinc, which is the anode,"},{"Start":"05:21.985 ","End":"05:28.925","Text":"and KOH gel, which is the electrolyte then silver oxide in graphite,"},{"Start":"05:28.925 ","End":"05:30.470","Text":"which is the cathode,"},{"Start":"05:30.470 ","End":"05:32.240","Text":"another layer like that."},{"Start":"05:32.240 ","End":"05:34.295","Text":"Then the steel cathode can."},{"Start":"05:34.295 ","End":"05:36.265","Text":"That\u0027s from top to bottom."},{"Start":"05:36.265 ","End":"05:40.709","Text":"In this video, we learned about a few primary cells."}],"ID":30327},{"Watched":false,"Name":"Secondary Cells","Duration":"5m 57s","ChapterTopicVideoID":28764,"CourseChapterTopicPlaylistID":292351,"HasSubtitles":true,"ThumbnailPath":null,"UploadDate":null,"DurationForVideoObject":null,"Description":null,"MetaTitle":null,"MetaDescription":null,"Canonical":null,"VideoComments":[],"Subtitles":[{"Start":"00:00.350 ","End":"00:02.595","Text":"In the previous video,"},{"Start":"00:02.595 ","End":"00:05.760","Text":"we learned about primary cells that are non-rechargeable,"},{"Start":"00:05.760 ","End":"00:07.155","Text":"and in this video,"},{"Start":"00:07.155 ","End":"00:11.085","Text":"we\u0027ll learn about secondary cells that are rechargeable."},{"Start":"00:11.085 ","End":"00:15.075","Text":"We\u0027re talking about secondary cells."},{"Start":"00:15.075 ","End":"00:18.780","Text":"The secondary cell can be recharged many times,"},{"Start":"00:18.780 ","End":"00:21.570","Text":"by passing electricity through the cell."},{"Start":"00:21.570 ","End":"00:24.990","Text":"The first example is lead acid battery."},{"Start":"00:24.990 ","End":"00:30.975","Text":"That\u0027s a car battery or an automobile battery. Here\u0027s a picture."},{"Start":"00:30.975 ","End":"00:32.715","Text":"The lead-acid cell,"},{"Start":"00:32.715 ","End":"00:34.590","Text":"contains several grids,"},{"Start":"00:34.590 ","End":"00:36.405","Text":"that act as electrodes."},{"Start":"00:36.405 ","End":"00:38.200","Text":"Here we see the grids."},{"Start":"00:38.200 ","End":"00:41.990","Text":"The electrodes are labeled as anode, that\u0027s negative,"},{"Start":"00:41.990 ","End":"00:43.625","Text":"and cathode positive,"},{"Start":"00:43.625 ","End":"00:46.805","Text":"according to their function during discharge."},{"Start":"00:46.805 ","End":"00:50.390","Text":"Remember they change sign during charging."},{"Start":"00:50.390 ","End":"00:55.265","Text":"Some people don\u0027t bother to call it anode or cathode in these batteries,"},{"Start":"00:55.265 ","End":"01:00.090","Text":"but just call it negative and positive electrodes."},{"Start":"01:00.170 ","End":"01:03.560","Text":"The order is anode separator,"},{"Start":"01:03.560 ","End":"01:06.230","Text":"cathode separator, and so on."},{"Start":"01:06.230 ","End":"01:08.645","Text":"The anode grids are linked together."},{"Start":"01:08.645 ","End":"01:12.190","Text":"Here we see them linked together as other cathode grids,"},{"Start":"01:12.190 ","End":"01:14.535","Text":"here the cathode grids linked together,"},{"Start":"01:14.535 ","End":"01:19.110","Text":"and the anode grids contains spongy lead,"},{"Start":"01:19.110 ","End":"01:22.745","Text":"and the cathode grids contained lead oxide."},{"Start":"01:22.745 ","End":"01:26.885","Text":"Now the cell has a low specific energy but can produce"},{"Start":"01:26.885 ","End":"01:30.740","Text":"a sufficient current for short times to start an engine."},{"Start":"01:30.740 ","End":"01:37.890","Text":"The electrolyte is 4.5 molar H2SO4 sulfuric acid, or f if you\u0027re in America."},{"Start":"01:39.490 ","End":"01:43.790","Text":"Let\u0027s look at what happens during discharging."},{"Start":"01:43.790 ","End":"01:47.785","Text":"Then the cell acts as a voltaic cell."},{"Start":"01:47.785 ","End":"01:50.165","Text":"The anode, the lead,"},{"Start":"01:50.165 ","End":"01:54.545","Text":"reacts with sulfite that comes from the sulfuric acid,"},{"Start":"01:54.545 ","End":"01:59.890","Text":"to give us lead sulfate plus H plus 2 electrons."},{"Start":"01:59.890 ","End":"02:07.540","Text":"At the cathode, lead oxide reacts with 3H+ plus HSO4-,"},{"Start":"02:07.540 ","End":"02:11.720","Text":"that\u0027s a sulfite from the sulfuric acid plus 2 electrons to"},{"Start":"02:11.720 ","End":"02:15.790","Text":"give us lead sulfate plus 2 moles of water."},{"Start":"02:15.790 ","End":"02:22.160","Text":"We get lead sulfate in both the anode and cathode."},{"Start":"02:22.160 ","End":"02:27.260","Text":"Now when we charge the cell,"},{"Start":"02:27.260 ","End":"02:29.510","Text":"it behaves as an electrolytic cell."},{"Start":"02:29.510 ","End":"02:35.375","Text":"We use electric energy to reverse the half-reactions."},{"Start":"02:35.375 ","End":"02:39.500","Text":"Now, each lead acid cell has a potential 2 volts, and usually,"},{"Start":"02:39.500 ","End":"02:44.450","Text":"a battery has 6 cells in series, plus, minus,"},{"Start":"02:44.450 ","End":"02:46.280","Text":"plus, minus, and so on,"},{"Start":"02:46.280 ","End":"02:50.395","Text":"with a total potential of 12 volts."},{"Start":"02:50.395 ","End":"02:57.245","Text":"Now the second example is lithium-ion cell that\u0027s used in laptops and mobile phones."},{"Start":"02:57.245 ","End":"03:00.380","Text":"There are many versions of lithium-ion cells,"},{"Start":"03:00.380 ","End":"03:03.925","Text":"and it\u0027s a very active field of research."},{"Start":"03:03.925 ","End":"03:07.970","Text":"Again, the electrodes are labeled as anode that\u0027s negative,"},{"Start":"03:07.970 ","End":"03:13.150","Text":"and cathode positive according to their function during discharge."},{"Start":"03:13.150 ","End":"03:15.530","Text":"Here\u0027s a picture, here\u0027s a cathode,"},{"Start":"03:15.530 ","End":"03:17.165","Text":"and here\u0027s the anode."},{"Start":"03:17.165 ","End":"03:20.060","Text":"Now, since lithium is very light,"},{"Start":"03:20.060 ","End":"03:23.795","Text":"lithium-ion batteries of a high specific energy,"},{"Start":"03:23.795 ","End":"03:28.370","Text":"and since lithium has a very negative standard electrode potential,"},{"Start":"03:28.370 ","End":"03:31.963","Text":"remember it\u0027s minus 3.05 volts,"},{"Start":"03:31.963 ","End":"03:38.755","Text":"the lithium-ion battery has a high maximum potential of 3.7 volts,"},{"Start":"03:38.755 ","End":"03:43.505","Text":"and can deliver more power than other batteries of comparable size."},{"Start":"03:43.505 ","End":"03:49.175","Text":"Now the anode consists of lithium atoms that lie between graphite sheets."},{"Start":"03:49.175 ","End":"03:55.685","Text":"It\u0027s called lithiated graphite and its form as Li_xC_6,"},{"Start":"03:55.685 ","End":"03:58.570","Text":"where x can lie between 0 and 1."},{"Start":"03:58.570 ","End":"04:01.650","Text":"Here, the graphite sheets,"},{"Start":"04:01.650 ","End":"04:04.920","Text":"near lithium is in-between them."},{"Start":"04:04.920 ","End":"04:08.584","Text":"The cathode consists of a lithium metal oxide,"},{"Start":"04:08.584 ","End":"04:10.115","Text":"which also has layers."},{"Start":"04:10.115 ","End":"04:14.680","Text":"The example is lithium cobalt 3 oxide."},{"Start":"04:14.680 ","End":"04:16.975","Text":"You can see the layers here,"},{"Start":"04:16.975 ","End":"04:19.384","Text":"with the lithium in-between."},{"Start":"04:19.384 ","End":"04:22.085","Text":"The cobalt are the small yellow ones,"},{"Start":"04:22.085 ","End":"04:25.685","Text":"and the white spheres are the oxygen."},{"Start":"04:25.685 ","End":"04:29.270","Text":"Now, lithium plus ions can move in and out of"},{"Start":"04:29.270 ","End":"04:33.965","Text":"the space between the layers, that\u0027s called intercalation."},{"Start":"04:33.965 ","End":"04:40.590","Text":"A typical electrolyte is 1 molar LiPF6,"},{"Start":"04:40.590 ","End":"04:46.040","Text":"that\u0027s called lithium hexafluoro phosphate in an organic solvent."},{"Start":"04:46.040 ","End":"04:48.695","Text":"There\u0027s a great deal of research on the subject."},{"Start":"04:48.695 ","End":"04:52.205","Text":"Many different electrolytes are used."},{"Start":"04:52.205 ","End":"04:58.325","Text":"Now during discharging, the lithium plus ions go from the anode to the cathode,"},{"Start":"04:58.325 ","End":"05:03.500","Text":"is discharging the ions going from the anode to the cathode."},{"Start":"05:03.500 ","End":"05:09.315","Text":"The anode, Li_xC_6 goes to x lithium plus,"},{"Start":"05:09.315 ","End":"05:12.135","Text":"plus x electrons plus C_6."},{"Start":"05:12.135 ","End":"05:13.950","Text":"That\u0027s the graphite."},{"Start":"05:13.950 ","End":"05:15.750","Text":"At the cathode,"},{"Start":"05:15.750 ","End":"05:21.270","Text":"Li_1-xCoO_2 plus x lithium plus,"},{"Start":"05:21.270 ","End":"05:26.295","Text":"plus x electrons, goes to LiCoO_2."},{"Start":"05:26.295 ","End":"05:28.565","Text":"When the battery is charging,"},{"Start":"05:28.565 ","End":"05:32.330","Text":"electrical energy is used to reverse the half-reactions,"},{"Start":"05:32.330 ","End":"05:36.094","Text":"and the lithium plus ions go in the opposite direction."},{"Start":"05:36.094 ","End":"05:38.020","Text":"Here we have charging,"},{"Start":"05:38.020 ","End":"05:42.800","Text":"here\u0027s the lithium plus ions going from the cathode to the anode."},{"Start":"05:42.800 ","End":"05:46.820","Text":"During discharging they go from the anode to the cathode,"},{"Start":"05:46.820 ","End":"05:53.020","Text":"and during charging they go from the cathode to the anode."},{"Start":"05:53.020 ","End":"05:57.990","Text":"In this video, we learned about rechargeable batteries."}],"ID":30328}],"Thumbnail":null,"ID":292351}]

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