Galvanic Cell - Video Tutorials & Practice Problems
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concept
The Galvanic Cell
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Now recall there are 2 types of electrochemical cells. 1 that produces electricity, and one that consumes it. In this video we're going to 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. And remember it utilizes this through the, through, redox reaction, We have oxidation where we lose an electron, reduction where we gain an 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 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. Alright. 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 2 types 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 following. So first we have our anode. Our anode for a galvanic cell is negatively charged. This is a metal electrode, a 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 the metal electrode and compartment where reduction occurs. Reduction means that we are gaining electrons. So if we take a look here, we have our galvanic cell, We have our anode compartment, which is the anode here is this metal rod. In this case, it's a zinc metal rod. The cathode here is positively charged, represents our copper electrode, this copper rod. Now, oxidation occurs at the anode, reduction occurs at the cathode. So if we're losing electrons, electrons are literally leaving this metal zinc electrode and they're heading towards my copper electrode. Now besides the anode and 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? How can an ion be neutral? It 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 buildup of cations within the anion half cell. So here this tube would represent my salt bridge. This tube is what connects both electrolytic, 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 bromide ions, would travel over here to the anode compartment. And then the Na plus ones, Na 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. But for right now just realize that the salt bridge is that tube that connects both half cells to each other. Within it we have neutral ions. Finally, we have a voltmeter, the device that record the amount of electricity generated by the elect by the galvanic cell. It's a voltmeter, so it measures voltage, which is capital v. And here's the voltmeter 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 anode to the cathode, so on this conductive wire we have electrons traveling, we're generating electricity. This voltmeter 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 sum.
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example
Galvanic Cell Example
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Which of the following statements is true for a salt 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. K. It's not atoms, it's ions. Its sodium ions flow to the magnesium cell half cell. Alright. So we know that the negatively charged ones like bromide ions would flow towards the anode compartment, and the positive ones, in this case sodium ions, would flow to the cathode compartment. Remember the anode 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 0 to plus 2. So its oxidation number increased, so it's being oxidized, which means it is the anode. Okay. So this would be the magnesium compartment or half cell. Cadmium goes from plus 2 to 0, so its oxidation number reduces, therefore it's the cathode. So we have our cathode compartment being the well, cadmium, compartment being the cathode. So if we look here, its bromide ions will flow to the magnesium half cell, so bromide is in fact yes. It should flow to the magnesium side because the magnesium compartment represents our anode, so this is true. It wouldn't flow to the cadmium half cell because that's where a reduction occurs. Its sodium ions should flow to the magnesium half cell. Now, sodium should be flowing towards the cathode side, which deals with the cadmium half cell. 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 2 half cell compartments, one for oxidation and the other for reduction. Remember the anode 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 key things. We're going to say for a galvanic cell, in terms of its electrodes, the anode is negatively charged and the cathode is positively charged. What effect will this have on the electrodes over time? Alright. So we know the anode is 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 ion. 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 2+ 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 2+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 anode. And let's say that this is what's left. The rest of it's gone, and you'll be losing electrons consistently over time, so you're losing the size of your anode. So here we'd say that the anode is our negative electrode, it loses electrons, and over time it causes a decrease in mass. Here we say that the anode 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 2+ions. The surface is becoming more and more negatively charged with the electrons it gains, which is going to attract these positive ions floating around. They're gonna move towards the surface. 2+ion seeing electrons on the surface connects 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 going to get bulkier, it's going to get bigger. It's gaining mass. We're gonna say the cap though gains electrons causing the surface to become more negatively charged attracting cations 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 anode department and positive ions go here towards the cathode department. But why exactly are these negative ions going towards the anode side? Well, what's happening? More and more positive ions are coming off of the anode, so your solutions would 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 cations 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 cations 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 cations that are being produced in the anode chamber. Now here, if we're talking about reactions, remember, zinc is being oxidized to zinc. So what would that look like? We'd have zinc solid being oxidized to zinc 2+ aqueous, and the 2 electrons that are lost. In the cathode compartment, copper 2+ is reduced, which means it gains 2 electrons to produce copper solid. We cancel out intermediates which in this case are the electrons, and what's left behind gives us our overall reaction. So here we have zinc 2+ink solid+2+2plusgivesmezinc2+ 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 3 electrons to become gallium solid. Gallium goes from plus 3 to 0, so its oxidation number was reduced, so it represents the cathode. Remember, we know that this is the cathode because the cathode is where reduction occurs. 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 1. Its oxidation number increased, so it's been oxidized, which means it's the anode. 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 3 electrons and one says only 1. You would multiply this equation by 3, so that both half reactions have the same number of electrons. Doing that tells me that 3 electrons are transferred between the sodium and gallium electrodes. Three electrons are lost by the anode half cell and given over to the cathode half cell, Right? So 3 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 redox reactions to produce and discharge electricity. So galvanic cells again are batteries. Now here they can make electricity, discharging means that the electron, 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 cell 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 Gibbs free energy, changes in your standard entropy total, so energy of the universe, our equilibrium constant k, equilibrium constant versus our reaction 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 0. We also talked about these other variables in other chapters. For us to be spontaneous, the change in your standard Gibbs free energy has to be less than 0. The change in your standard total entropy has to be greater than 0. Your equilibrium constant k has to be greater than 1. 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 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 it's produced. So 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 Gibbs free energy is equal to 0. Change in my standard entropy total is equal to 0. Your equilibrium constant k is equal to 1, k is equal to q, and your standard cell potential is equal to 0. So just remember, a galvanic cell represents a spontaneous electrochemical cell because it utilizes spontaneous redox reactions. If it 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 2. Alright. 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 1, 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 1, it's spontaneous. Has a negative change in my standard Gibbs free energy and produces electricity, that is true. If it's spontaneous, it's a galvanic cell. Galvanic cells utilize, a redox reaction in order to produce electricity. Here, the Gibbs free energy would have to be less than 0, making it negative. Has discharged all electricity and is a dead battery. That only be true if k was equal to 1, which it's not. Is spontaneous, okay, and has a negative standard cell potential. So the first part is true, it is spontaneous, but its standard cell 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.