Learn about Senior Chemistry, Redox 9, in this comprehensive video by bannanaiscool.
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Rob Lederer: What do we have here? This is a voltaic cell. It's named after Alessandro Volta who started inventing these things around 1800. They are also called galvanic cells because of -- what was his name? Luigi Galvani. He is one who was credited with discovering electricity. They are all Italians, aren't they? Chemguys have Italian. So, what we've got here is this voltaic cell made of zinc and copper with a copper to nitrate solution in the beaker and inside this porous cup is zinc nitrate. Sometimes you'll see voltaic cell set up and I'll give you this in the diagram in a second with two solutions separated, but connected with something called a salt bridge or a U-tube. So, when the zinc goes into the zinc nitrate and you've got a connection between the two made by the porous cup allowing movement of ions through the cup. You get registered on the meter a positive voltage, which means that there is a current flowing from the anode to zinc to the copper, which is the cathode. Now, which is which and how do you tell them what ions are flowing? Oh that's coming right now. So, if we can take two half reactions one where an electron is being lost, electron are being lost, and then gained. We can then intercept the flow between the reducing agent who is losing electrons, the oxidizing agent who is gaining them; that electron flow or electricity we can utilize for power to be able to use cameras to film Chemguy with that reason or calculators, battery power, portable electricity, portable power absolutely vital. This was discovered about 130 years ago. Well, let's take this reaction here written in what we call cell notation and let's draw what the voltaic cell would like. A voltaic cell is an electro chemical cell that will produce an electrical current. So, this voltaic cell or galvanic cell -- this one is going to be made from dichromate ions and hydrogen ions, acidified dichromate and the carbon here is very interesting and it needs to be there and I'll show you why as we do the diagram. This reaction, which is actually the SOA because it's gaining electron is going to react with a piece of tin in a tin-tuned nitrate solution. This solution might be the potassium dichromate, this also could be H2so4, Hcl something like that. So, we've got this half reaction for this right here and we can either build that half reaction or we can just look on a data chart, on a reduction potentials chart because it's probably there, a very popular reaction, and so is the tin one. Remember the highest one on the left directs the lowest one on the right and through this list of chemicals here that's what we've written here. Now, this is going to be the half reaction that gains electrons that gaining electrons is reduction, I mean this is an oxidizing agent, but here is what it means in terms drawing the cell or building the cell. Because its reduction would be the reaction that occurs at the cathode or in the half cell half reaction. The half cell has the cathode in it and this is the half reaction that's going to occur at the anode. So anodes for oxidation, the two valves go together, cathodes for reduction and the two consonants go together. Now, when we put this together, we are going to get a total voltage of 1.37 volts on a voltmeter under standard conditions and that's -- you have actually take into account the fact that there is resistance in the wiring and in the apparatus we are using where you might not might get the proper voltage registered. So, remembering that all of this here describes what's happening in anode and cathode, let's put this together now in diagram form.