Galvanic Cell - Video Tutorials & Practice Problems
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concept
The Galvanic Cell
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Now recall there are two types of electrochemical cells. One that produces electricity and one that consumes it in this video. We're gonna take a look at galvanic cell. Remember galvanic cell or sometimes called a voltaic cell is a spontaneous electrochemical cell that produces electricity. And since it's making electricity, it's basically a battery. Here, we're going to say the way it does this is it uses stored chemical energy and converts it into electrical energy. I remember it utilizes this through the um through uh redox reaction, we have oxidation where we're losing electron reduction where we're gaining electron. The transferring of this electron through a conductive wire is what produces our electricity. So just remember our galvanic cell is spontaneous, it produces electricity. So in essence, it's a battery. It's utilizing uh the chemical energy of a redox reaction and converting it into a electrical energy source.
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example
Galvanic Cell Example
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Here, it says the purpose of a galvanic cell is to a purify solids. B allow for only oxidation C generate electricity D to consume electricity. All right. So first of all, we never talked about purifying solids in any way. So we know that's not gonna be an answer. A galvanic cell is a type of electrochemical cell where both oxidation and reduction occur. And then remember we have two typess of electrochemical cells. One that can produce electricity and one that consumes it. Galvanic cells happen to be the ones that produce electricity or generate electricity in this case. So C would be our answer. D would not be our answer. So our final option here is choice C.
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concept
Galvanic Cell Components
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Now the major components of a galvanic cell are given as the fault. So first, we have our a node, our a node for galvanic cell is negatively charged. This is a metal electrode and compartment where oxidation occurs. Remember, oxidation means we are losing electrons. Then we have our cathode compartment. This is our positively charged electrode. So this is a metal electrode and compartment where reduction occurs, production means that we are gaining electrons. So if we take a look here, we have a galvanic cell. We have our anade compartment which is nega the ade here is this metal rod. In this case, it's a zig meat. The cathode here is positively charged represents our copper electrode. This copper rod. Now oxidation occurs at the a node reduction occurs at the cathode. So if we're losing electrons, electrons are literally leaving this metal zinc electrode and they are heading towards my copper electrode. Now, besides the adem the cathode, we have a salt bridge. This is a tube that connects both half cells to one another and allows for the flowing of neutral ions. Now, neutral ions may not make sense, right? Ion be neutral, has a positive and a negative charge. Well, here, when we say neutral ions, they're just a special type of spectator ions within the solution that possess no acidic or basic properties. Ions can be acidic, basic or neutral depending on their origin. Here, we're only using the ions that are neutral in nature. They're not acidic or basic. Now, here, what's the whole purpose of the salt bridge? Its purpose is to neutralize the build up of C ions within the anion have sub. So here, this tube would represent my salt bridge. This tube is what connects both electrolytic uh well, electrolyte solutions to one another. It's connecting both half cells to each other. Within this, we have neutral ions typical neutral ions are sodium ions, potassium ions, bromide ions. Here, we're going to say that the negative negatively charged ones like bromine ions would travel over here to the animal compartment and then the N A plus ones N A plus or K positive would go towards this side towards the cathode compartment. Later on, when we talk about electrodes a little bit more specifically, we'll talk about why this is necessary. We right now just realized that the salt bridge is that tube that connects both half cells to each other within it. We have neutral ions. Finally, we have our vault meter, the device that record the amount of electricity generated by the elec by the galvanic cell. It's a volt meter source measures voltage which is capital V. And here's the volt meter here, this little circular thing here, we're gonna put a V because it's measuring voltage. So as electrons, as electrons travel from the A O to the cathode. So on this connective wire, we have electrons traveling we're generating electricity. This volt meter will give us a reading of value of the amount of electricity that's being produced. Right? So here we just have the fundamental and major components of any given galvanic slash voltaic.
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example
Galvanic Cell Example
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Which of the following statements is true for assault bridge with the following redox reaction, right? So here we're talking about what side would my bromide ions flow c contains neutral atoms that interact with the ions in both half cell compartments. We know that the salt bridge itself doesn't contain atoms which are neutral, it deals with neutral ions. So this is not correct. OK. It's not atoms, it's ions, it's so flow to the magnesium cell have. So, all right. So we know that the negatively charged ones like bromide ions would flow towards the adult compartment and the positive ones in this case, sodium ions would flow to the catholic compartment. Remember the A node is where oxidation occurs and the cathode is where reduction occurs. Here. If we take a look at our overall redox reaction, we have magnesium going from zero to plus two. So its oxidation number increased. So it's being oxidized, which means it is the A node. OK. So this would be the magnesium compartment or have some cadmium goes from plus 2 to 0. So its oxidation number reduces. Therefore, it's the cathode. So we have our catholic compartment being the or cabin uh compartment being the catholic. So if we look here, it's bromide ions will flow with the magnesium half salt. So bromide is, in fact, yes, it should flow to the magnesium side because the magnesium compartment represents our Anno. So this is true, it wouldn't flow to the cadmium half cell because that's where a reduction occurs. If sodium ions flow should flow to the magnesium half cell, no sodium should be flowing towards the cathode side which deals with the cadmium half C. So out of all our options, only A is correct.
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concept
Galvanic Cell Electrodes
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In this video, we're gonna take a look at the galvanic cell electrodes. Here we're going to say recall all electrochemical cells possess two half cell compartments, one for oxidation and the other for reduction. Remember the A node equals oxidation and a way to remember that is an ox and then the cathode equals reduction. A way to remember that is red cat. Now, before we start filling in the rest of this, let's just talk about some he things we're gonna say for a galvanic cell in terms of its electrodes, the A node is negatively charged and the cathode is positively charged. What effect will this have on the electrodes over time? All right. So we know the anodes where oxidation occurs here. We're looking at the zinc electrode much more closely and we're gonna say that zinc is being oxidized to zinc on. Now, what's happening here is electrons are literally leaving the electrode and traveling towards the cathode. The cathode is positively charged, it's gaining electrons here. Copper two plus would be reduced to copper solid. Now, what effect is this gonna have? We're going to say here, we see our zinc solid surface here and what's happening is we have electrons traveling up the electrode leaving the electrode to go to the cathode. What effect does this have? Well, my zinc is losing electrons as a result of this, it starts to produce zinc two plus ions which become more and more dissolved within my solution. So, electrons don't weigh very much. But over time, if you keep losing electrons, those little masses do add up, eventually, you're gonna lose a good chunk of this animal. And let's say that this is what's left the rest of it's gone and you've been losing electronic consistently over time. So you're, you're losing the size of your Anno. So here we'd say that the A node is our negative electrode. It loses electrons and over time it causes a decrease in mass. Here we say that the A node dissolves away what's happening to the cathode. Well, the cathode is our positive electrode. Yes. But over time it's gaining more and more electrons. These electrons are depositing themselves onto the surface of the cathode. It is in a solution of its own ions. In this case, copper two plus ions, the surface is becoming more and more negatively charged with the electronic games which is going to attract these positive ions floating around. They're gonna move towards the surface two plus ion seeing electrons on the surface next to them negative charge positive charge neutralize each other. So the copper ions are gonna start to coat the surface of this electrode. So over time, the cathode is gonna get bulkier, it's gonna get bigger, it's gaining mass. You're gonna say the cathode gains electrons causing the surface to become more negatively charged, attracting C ions to it. And this over time causes an increase in mass. Here, we would say that the cathode plates out one gets skinnier, one gets bigger. Now, here we talked about our salt bridge in earlier videos, remember a salt bridge there just has neutral ions within it. So we know that the negative ions here would go towards the anote compartment and positive ions go here towards the catholic compartment. But why exactly are these negative ions going towards the anodes side? Well, what's happening more and more positive ions are coming off of the Anno? So your solutions can become saturated with these positive ions so much so that if too many of them are hanging around the electrolyte solution is super positive, these negative electrons won't want to leave. They'll be like why should I leave if my solution has all these dissolved positive ions around opposite charges attract. That's why we need a salt bridge. The salt bridge has these negative ions go into the solution neutralizing these positive C ions that are being produced, keeping their concentration down. And in that way, the electrons are not conflicted. Do I go towards the cathode? Which is becoming less positive over time as it gains more and more electrons on its surface or should I stick around and hang out with these dissolved cation ions in my solution. Here, electrons don't have to worry about that because again, the negative ions within the salt bridge are neutralizing these excess cation ions that are being produced in the A node chamber. Now, here, if we're talking about reactions, remember, um zinc is being oxidized to zinc. So what would that look like? We'd have zinc solid being oxidized to zinc? Two plus aqueous and the two electrons that are lost in the catholic compartment. Copper two plus is reduced, which means it gains two electrons to produce copper solid. We can't slot intermediates which in this case are the electrons. And what's left behind gives us our overall reaction. So here we have zinc two plus or zinc solid plus copper two plus gives me zinc two plus plus copper solid. So this would be the overall reaction that occurs from this electrochemical cell dealing with our zinc electrode and copper electrodes.
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example
Galvanic Cell Example
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How many electrons will be transferred between a sodium and gallium electrode from the following. So here we have gallium ion absorbing three electrons to become gallium solid gallium goes from plus 3 to 0. So its oxidation number was reduced soon represents the catholic. Remember we know that this is the cathode because the catheters were a reduction of hers. Also we know that this is a reduction because the electrons are reactants, sodium. On the other hand goes from a neutral charge to plus one, its oxidation number increased. So it's been oxidized, which means it's the a node. We also know it's an oxidation because your electrons are products. Now remember your electrons are intermediates and they have to cancel out with each other. Here, they can't because one says three electrons and one says only one you would multiply this equation by three. So that both half reactions have the same number of electrons doing that tells me that three electrons are transferred between the sodium and gallium electrodes. Three electrons are lost by the A node, half cell and given over to the cathode half cell, right. So three electrons will be transferred within this particular example question.
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concept
Galvanic Cells and Spontaneity
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Now, in terms of spontaneity, we can say that a galvanic cell uses spontaneous read out reactions to produce and discharge electricity. So galvanic cells again are batteries. Now here they can make electricity discharging means that the electro, the energy that we've made, the electricity that we've made, we start to use it and that means we're discharging it. Now, here we're going to say all spontaneous reactions have a positive standard self potential value. So here we're gonna talk about galvanic cells. They use spontaneous redox reactions. And how does that relate to our different variables? We're also gonna talk about what happens when we're at equilibrium. So the variables we're gonna look at here are changes in your standard gifts, free energy changes in your standard entropy total. So energy of the universe are equilibrium constant K equilibrium component versus our reactions. Ocean Q and of course, our standard cell potential, we already said that galvanic cells use spontaneous redox reactions and that all spontaneous redox reactions have a positive standard cell potential. So that means that this would have to be greater than zero. We also talked about these other variables in other chapters for us to be spontaneous. The change of your standard gives free energy has to be less than zero. The change in your standard total entropy has to be greater than zero. Your equilibrium cost, the K has to be greater than one. And then if we're talking about K versus Q here, we'd have to say that our equilibrium constant K would have to be greater than Q. Now, what happens if our galvanic cell makes all this electricity and decides to use it to use all of it, it's completely discharged all of its electricity. Well, in that case, what happens when you use all the electricity of a battery, it goes dead. But in chemistry, we, we don't like to say dead. We like to say that it's reached equilibrium. So at equilibrium, our galvanic cell has used up all of its electricity that's produced. So in essence, it's a dead battery here. That would just mean that each of these variables are equal to these same values. So change in standard gifts free energy is equal to zero. Change in my standard entropy total is equal to zero. Your equilibrium constant K is equal to one K is equal to Q and your standard cell potential is equal to zero. So just remember, a galvanic sub represents a spontaneous electrochemical cell because it utilizes spontaneous redox reactions. If were to use all of the electricity that it's produced, it would reach equilibrium where this is true for each one of these variables.
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example
Galvanic Cell Example
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A reduction reaction with an equilibrium constant of 4.8 times 10 to the two. All right. So remember your equilibrium constant here is K and we're talking about which of the following statements is true. K here is greater than one, which means that it, it is a spontaneous reaction is non spontaneous. We don't need to continue reading. We know that this is not true since K is greater than one, it's spontaneous as a negative change in my standard gives free energy and produces electricity. That is true. If it's spontaneous, it's a galvanic cell, galvanic cells utilize um a redox reaction in order to produce electricity. Here, the Gibbs free energy would have to be less than zero, making it negative has discharged all electricity and is a dead battery. That only be true if K was equal to one which it's not is spontaneous. OK. And has a negative standard self potential. So the first part is true, it is spontaneous, but it's standard self potential should be positive and not negative. So here only option B is correct.
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Problem
Problem
Which of the following is false about a Voltaic cell?
A
Anode electrode dissolves while cathode electrode plates out.
B
It changes chemical energy into electrical energy.
Half reaction with more negative reduction potential attracts electrons and undergoes reduction.
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Problem
Problem
For the redox reaction label: the anode, cathode, half-reactions occurring at each half-cell, direction of electron flow, and direction of neutral ions flow.