16. Electroanalytical Techniques
Voltammetry
16. Electroanalytical Techniques
Voltammetry - Video Tutorials & Practice Problems
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Voltammetry
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So galvanic or voltaic cells represent spontaneous cells that produce or discharge electricity. Now when they fully discharge their electricity, they become a dead battery. Now we use the word battery because these things are creating electricity. Now with your typical type of galvanic or voltaic cell, we have two jars which represent electrochemical cells separated for one another. They are connected here by this salt bridge. Typically dipped inside of each one of these jars is a piece of metal which represents an electrode here we have electrode one, an electrode to within a galvanic. Overall take cell. The negatively charged electrode is called the anodes and the positively charged electrode is called the cathode. Now whether this is a spontaneous cell, like a galvanic or voltaic cell or non spontaneous cell which is called an electrolytic cell, it doesn't matter. This is always true. We're going to say that the anote always undergoes oxidation, so it will lose electrons and the cathode undergoes reduction where it gains electrons. This is illustrated by the fact that these electrodes are connected by a wire and we can see electrons leaving the anodes and heading down towards the cathode. This movement of electrons in one direction. So here we have our ad out here we have our cathode. So we have movement of negative electrons from the an ode to the cathode. But in order to complete the circuit, we need the movement of negative charges in the opposite direction. So negative charges have to move from the cathode to the anodes. What do these negative charges come from? Well, they come from the salt bridge itself inside the salt bridge we have inert ions. So typically chloride ion and nitrate ion, they move from the cath outside to the an outside. What is the point of doing this? Well if we take a look here, we have two half reactions written. We have at the cathode we have the reduction of copper to ion. So we're gonna say here that three moles of copper, two ion absorb six moles of electrons to become three moles of neutral copper solid at the same time at the anodes we have two chromium solids, losing six electrons to become to chromium three ions. So what's happening here is we're gonna say that this represents our chromium solid and this here represents our copper solid. We have the generation of copper three ions here and here's the thing, negative electrons are leaving my an out and going towards my calf out. But if there's a large build up of these positive ions here that will prevent the electrons from moving from the No to the cath outside because the build up of positive electrons here will attract these negative electrons and prevent them from moving from the No to the cathode. So how do I get rid of these positive ions that are generated? The salt bridge? The salt bridge releases the negative ions into here. They combine with these positive ions and neutralize them. So in a way we we depress or suppress the amount of positive ions generated here at the same time we have these copper two ions floating around here. And as these electrons come and attached to the cathode, the surface of the cathode is gonna become negatively charged. And what's gonna happen is the negatively charged surface is going to attract these positive ions here. They're going to attach themselves to the surface of the cathode electrode and solidify. So what's gonna start happening here is that you're gonna get an n crusting of these ions once they touch the negative surface they're gonna solidify into neutral metal. So we're gonna say that the cathode plates out at the same time the anad is losing electrons. So over time this electrodes gonna diminish in size. It's gonna shrink. Okay so we're gonna have less and less of the metal present. So we're gonna say here that the anna dissolves away over time. Now ionization energy is the energy necessary to remove an electron. We want the anodes to lose electrons easily so that they can go to the cathode. So you want the ionization energy here to be low at the same time. You want electrons to move from the an outside to the cathode side. You want them to n crust themselves on the surface of this cathode as much as possible, electron affinity. Is the liking of electrons to an ion or some surface here. You want the electron affinity to be high? You want that electrode surface to really want those electrons to attach their. Now how would we produce more voltage which is e in terms of the load compartment, you'd want to make sure that these positive ions again are very low so as to not prevent electrons from leaving the anodes and go to the cathode again. The salt bridge helps with that. So you want the concentration of an ode ions to be low at the same time. You want the positive ions here to be high because the more concentrated the solution becomes with positive ions the mortal attract electrons from the outside to the cathode side. So you want the catholic compartment to be high in terms of concentration there's a lot that goes into explaining what's going on with this galvanic oval takes out. These are the most important concepts to keep in mind when talking about it with ionization energy. We can talk about it in terms of the half reactions that we see here. So the and it would just be the equation that we have here would represent the ionization energy involved. We're losing electrons to become a positive ion. And the catholic equation here would represent electron affinity. The positive ions gain electrons to become neutral. And remember here later on we'll talk about how this movement of electrons from the and outside to the cath outside and how this reverse movement of the negative ions of chloride and nitrate from the catholic side to the end outside helps produce voltage will tie it into the idea of self potential and this idea of self potential will use it in terms of reduction half reactions. Now here all of these are written as reductions because here we have electrons as reactant, we have the elements absorbing these electrons to become more negatively charged. Remember reduction is accepting of electrons and becoming more negative in terms of your oxidation number. Now hear each of them have a self potential involved Later on we'll be able to determine our self potential based on information given to us by a galvanic cell for take cell, realize here when it comes to self potential, we're gonna say higher self potential or or yeah, hire yourself potential means more likely for reduction. Okay, so the higher self potential is for half reaction, the more that particular element wants to be reduced. And we're gonna say that the lower yourself potential than the more likely for oxidation. Remember also if you are more likely for oxidation, that would make you the stronger reducing agent. And then here, if you're more likely to be reduced, that makes you the stronger oxidizing agent. So keep in mind when it comes to galvanic or voltaic cell, we have the generation of electricity. If too much electricity is spent in the process, we become a dead battery when it comes to galvanic or voltaic cell, we are a spontaneous cell Later on, we'll talk about the variables necessary to represent spontaneity when it comes to sell potential, as well as other variables we discussed in the past. But keep in mind for now the basic layout of a typical galvanic or voltaic cell, and the different concepts, as well as theories involved.