- 6/5/2025
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LearningTranscript
00:00Hello everyone. Welcome to this exciting lecture series on electrochemistry.
00:07In this video, we will study about a quick topic named standard electrode potential.
00:16So, according to IUPAC, the electrode potential has been defined as follows.
00:23In electrochemistry, the electrode potential is the electromotive force of a cell
00:29built of two electrodes. It is denoted by the sign E.
00:34So, whenever we have a cell, the electromotive force between two electrodes will be the cell potential
00:42or the electrode potential. Whether it is an electrochemical cell or the electrolytic cell,
00:49the difference between the electromotive force between the two electrodes will always correspond to the standard electrode potential.
00:56Sorry, the electrode potential. We will study about the standard electrode potential in the coming slides.
01:05Now, moving toward the measurement of electrode potential.
01:11Measuring the absolute potential of a single electrode on its own is actually not possible with current experimental methods.
01:20This is because electrode potential is inherently a relative quantity.
01:25It depends on the interaction between two electrodes rather than existing as an independent absolute value.
01:32So, when we talk about electrode potential, what we really mean is the potential difference between two electrodes.
01:39Only the difference in potential between the two electrodes can be measured experimentally.
01:50Since absolute electrode potential cannot be measured directly, scientists measure the potential difference between two electrodes instead.
01:58This potential difference is what we call the cell potential or electromotive force.
02:03By connecting two electrodes and measuring the voltage between them, we can gather important information about their relative tendency to gain or lose electrons also,
02:14which help us understand their chemical behavior.
02:18To measure the potential of an unknown electrode, we set up an electrochemical cell with two electrodes.
02:27One electrode will be a reference electrode.
02:30This is a well-characterized electrode with a known value and which have a stable potential.
02:40Common examples include the standard hydrogen electrode or the saturated column electrode.
02:48The other electrode is the one whose potential we want to find.
02:53By comparing the unknown electrode against the roughness, we can calculate the unknown electrode's potential.
03:06When the cell is set up, we measure the overall cell potential, often denoted as E.
03:14This measured value is essentially the algebraic sum of electrode potential of both electrodes involved in the cell.
03:22It is important to note that the cell potential is what we measure directly and from it we can infer the potential of the unknown electrode using the known potential of the reference electrode.
03:35Here is the key equation to remember.
03:37The cell potential is the sum of the potentials of the cathode and the anode.
03:43Conventionally, the cathode is where reduction occurs and has a certain potential, while the anode is where the oxidation occurs and has another potential.
03:55By using this relationship, we can break down the cell potential into its components.
04:02In this slide, we will look into a standard hydrogen electrode, which can be used as a reference electrode in the measurement of standard electrode potentials.
04:16So, here is a simple diagram.
04:17We see that, first of all, there is a platinum electrode.
04:22Okay.
04:23So, this platinum electrode is connected with the platinum wire.
04:27Hydrogen gas at a pressure of about 100 kilopascal is introduced into this cell or the glass, which goes into the solution.
04:38Here is a glass bell around the platinum wire and the electrode, where an opening allows the hydrogen gas to bubble out of the solution.
04:48The molarity of the solution is 1.
04:51It means 1 mol per decimeter cube of the concentration of the H plus signs.
05:00In electrochemistry, understanding the tendency of a species to gain or lose electrons is crucial.
05:07This tendency is quantified using electrode potential.
05:12The potential of a half reaction, which is a half cell, measured against the standard hydrogen electrode under standard condition is called the standard electrode potential for that cell or the half reaction.
05:25Okay.
05:26The standard condition for this to measure the standard electrode potential, if the temperature should be 298 Kelvin or 25 degrees centigrade,
05:36pressure should be 1 atmospheric for gases, and concentration of the electrolytic solution should be 1 mol, which is the 1 mol per liter of solution.
05:49Okay.
05:50The potential of a half cell reaction is measured against the standard hydrogen electrode.
06:02The standard hydrogen electrode is a gas sign electrode, which can be seen here, and we have studied about it in the previous slides.
06:12The standard hydrogen electrode is used as a reference electrode for determination of standard electrode potential of elements and other half cells, which are used in the other cells.
06:28The standard hydrogen electrode is assigned an arbitrary potential of zero volts under the standard condition to provide a baseline for measuring other electrode potentials.
06:38This reference allows the determination of standard electrode potential of elements and the other half cells by comparing their voltages against the standard hydrogen electrodes.
06:49The standard electrode potentials.
06:50The standard electrode potentials are fundamental for predicting the direction of redox reaction and the electrochemical behavior of different substances.
07:02Here we can see the more clear view for measuring the electrode potential.
07:09The one side of the side of the electrochemical action, it have the standard hydrogen electrode and in the other side, we have the another metal whose potential is to be measured.
07:25So by comparing the voltage between a hydrogen electrode and the zinc electrode, we can measure their strong potential.
07:32We can measure the voltage from this voltmeter also.
07:37Here is a salt bridge between these two solutions.
07:40The function of the salt bridge is to migrate from the one side to the other side.
07:46So the accumulation of charges in both of these solutions should be avoided.
07:54So the basic function of the salt bridge is to maintain the neutrality in both of these beakers or the two half cells.
08:03If there were no salt bridge, some of the ions will accumulate in one cell and the other ions will accumulate in the other cell and the reaction would stop in some time.
08:16On this slide, we will explore why standard electrode potentials are so important in electrochemistry.
08:25These potentials are not just numbers.
08:27They tell us how strongly a substance wants to gain or lose electrons.
08:32In practical terms, they help us understand which chemicals act as an oxidizing agent and which act as a reducing agent.
08:41So how we can predict the spontaneity, spontaneity and direction of the redox reactions.
08:48First of all, the first point relates to identifying the oxidizing and reducing agent based on standard electrode potential.
08:58A higher value of E0 means the species is a stronger oxidizing agent.
09:04It really wants to gain electrons and gets reduced.
09:09Conversely, a lower value of E0 means the species is a stronger reducing agent, which means it is more likely to lose electrons and gets reduced.
09:21So the position on the standard electrode potential scale directly reflects how reactive a substance is in terms of electron transfer.
09:32Now we will talk about determining the reaction direction.
09:38It is the second key use of the standard electrode potential.
09:42Ok.
09:43When two substances react, the one with the higher standard electrode potential will typically undergo reduction.
09:50Ok.
09:51While the one with the lower potential will undergo oxidation.
09:55This means that we can look at a pair of half cell reactions and determine not only which direction the electrons will flow,
10:10but also whether the overall reaction will be spontaneous under standard condition or not.
10:15This is an extremely useful tool in both lab experiments and in the industrial applications.
10:29So that is the end of our lecture.
10:32I hope that you have learned something new.
10:35Thank you very much.
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