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Voltaic Cells - Concept

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Teacher/Instructor Jacqueline Spivey
Jacqueline Spivey

Ph.D.,U.C.Santa Cruz
Teaching at a top-ranked high school in SF

She teaches general and chemistry at a top-ranked high school in San Francisco. Prior to that, she lead and published a number of research studies and lectured at SF State University.

A voltaic cell is the device in which the transfer of electrons takes place through an external pathway. The flow of electrons in a voltaic cell enable energy in form of electricity to be produced in redox reaction. The set-up of a voltaic cell includes an anode, a cathode and a salt bridge that is used to neutralize the system.

This segment let's go ahead and discuss voltaic cells also known as galvanic cells and you might actually interact, I mean hear them called electrochemical cells. That's kind of the broader term. So again this falls under the heading of electrochemistry which means that we're talking about oxidation reduction reactions. Again remember they're coupled and they involve the transfer of an electron. So more specifically, a voltaic cell is a device in which the transfer of electrons takes place through an external pathway rather than directly between the reactants. And in a moment I'm going to show you a picture and kind of discuss how that occurs.

So basically what's happening is that we're harnessing the energy from a spontaneous redox reaction and using it to do work and in this case the work is the transfer of electrons. So you have one cell that has the half reaction that involves redox and one cell that involves the half reaction for the oxidation part. So one cell for the reduction, one cell for the oxidation, and that creates a flow of electrons through the external circuit. Okay, so basically in this case let's go look at kind of a depiction of this.

So let's call this our voltaic or galvanic cell. So we're going to have this side over here on the left is where our oxidation half cell and this guy on the right is our reduction half cell. And so here we're going to have a piece of zinc and a reducing agent solution, an electrolytic solution, the zinc sulphate. Okay? And so this zinc sulph- this zinc solid is going to serve as our anode and this is where the oxidation is occurring. And then over here on the right hand side, we have our half cell where reduction is taking place and we've got a piece of copper and a copper sulphate electrolytic solution and that's where the reduction is occurring. So remember negative over here for oxidation because this is losing of electrons. Reduction is positive because this is the gaining of electrons.

So we have the electron flow going form this side we call the anode, flowing over to the cathode. Alright. So then here, we have this guy that's called the salt bridge and the salt bridge consist of in this case, sodium nitrate in our fake kind of voltaic cell. And that's because sodium nitrate is just a salt which means it's going to break up into its ionic parts, sodium and nitrite. And you'll recall from your understanding of displacement reactions or replacement reactions, that these guys are just going to break up and they're just going to be spectator ions. Okay. So they just serve a purpose for basically making sure that these two solutions here, these electrolytic solutions remain electrically neutral so that the electrons are only flowing through here.

So this electron flow will be registered in this case by a voltmeter. But you can attach it to anything else of your choosing that would allow you to show how the energy was harnessed. And that is voltaic cells.