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ემზადებით გამოცდისთვის? მოემზადეთ ამ 6 გაკვეთილის დახმარებით შემდეგ თემაზე: Redox reactions and electrochemistry
იხილეთ 6 გაკვეთილი
ვიდეოს აღწერა
- [Voiceover] Before we get into shorthand notation let's review the structure of the Galvanic or Voltaic Cell. Remember, a Voltaic Cell uses a spontaneous redox reaction to create an electric current. And so, we already know what happens on this electrode on the left, the Zinc electrode or the solid Zinc turns into Zinc 2+ ions. So think about an atom of Zinc turning into Zinc 2+. The atom will have to lose two electrons, so two electrons are left behind on the Zinc electrode. Let's write out that half reaction. So we have solid Zinc losing two electrons to turn into Zinc 2+ ions in solution. So this is the losing two electrons, so we put the electrons on the product side. This is our oxidation half-reaction, so this is an oxidation. So we've lost electrons, remember, when you lose electrons it's an oxidation reaction, or you could also look at the oxidation states. Those two electrons that we lost, these two electrons right here, are going to travel along our wire. So we have a wire set up and those two electrons are going to move, which is our electric current, right? So we get an electric current in our wire, and those two electrons move over to the electrode on the right, which is Copper. So now we have these two electrons on our Copper electrode. In solutions, this is an aqueous solution of Copper sulfate, so we have Copper 2+ ions in solution. And when those Copper 2+ ions come in contact with those electrons we get a reduction half-reaction. So let's write it up here. So Copper 2+ ions are going to gain two electrons. Gain of electrons is reduction. So think about what happens if you add two electrons to a Copper 2+ ion, you get solid Copper, right? So overall zero charge. So this would be solid Copper, and since we gained electrons this is our reduction half-reaction, so this represents a reduction half-reaction. So remember, loss of electrons is oxidation, and gain of electrons is reduction. So "Leo the Lion Goes Ger", is a good way to remember oxidation and reduction. If we add together our two half-reactions we get our overall redox reaction. So we add these together, and we know that the two electrons that were lost by Zinc are the same electrons that are gained by Copper 2+, we can cancel those out, and so for our reactants we will have solid Zinc and we will have Copper 2+ ions, so we write that in here. So it's solid Zinc plus Copper 2+ ions. And for the products, over here we would have Zinc 2+ ions and solid Copper. So this gives us, Zinc 2+ ions in solution and also solid Copper. So, over time, if you think about what happens, we're losing Zinc, so let me use a different color here, so we're gonna lose Zinc over time and we're going to gain Copper, right? So we're going to get more Copper deposited on our Copper electrode, so think about more Copper, more Copper deposited on the surface of our Copper electrode. So that's our spontaneous redox reaction that's creating an electric current because of the flow of the electrons in the wire here. Let's go back to our half-reactions and think about the electrodes. So we know that oxidation occurs at the anode, so this must be our anode. And we know that reduction occurs at the cathode, so this must be the cathode. And a good way to remember this is an ox and red cat, right? So, an ox, oxidation occurs at the anode, and then red cat, let me write that one down over here, so red cat, reduction occurs at the cathode. Alright, let's also think about the salt bridge really quickly, alright? So we have, let me go ahead and use red here, we have sulfate, we have sulfate anions in our salt bridge, and anions migrate to the anode. So anions migrate to the anode, that's easy to remember that. So these anions are going to migrate this way. And cations migrate to the cathode, so we have sodium cations here, and cations migrate to the cathode. So it's easy to remember what's happening in the salt bridge. Alright, now finally let's think about shorthand notation. So it's a little bit annoying to draw out a picture like this every time you want to represent a Voltaic Cell, so there's a shorthand notation that's used so you don't have to keep drawing things out. And so let's go ahead and start writing our shorthand notation. First you put your electrode, you put your anode. So our anode here, our anode is Zinc, so we have solid Zinc, let me write that down here. So it's solid Zinc. Next you draw a single vertical line which represents a face boundary between solid Zinc and your aqueous solution of Zinc 2+ ions, so we're gonna write our Zinc 2+ ions in here. So we've represented, let me use red for this, we've represented our Zinc electrode and we've represented our Zinc 2+ ions. Next we draw a double vertical line, and this represents our salt bridge. So the double vertical line represents our salt bridge. And next we put Copper 2+. So we have Copper 2+, let me circle this in green, Copper 2+ ions, so we write Cu 2+. And next we draw a single vertical line again representing a face boundary, because now we put our other electrode, our cathode, and our other electrode would of course be solid Copper, so let's go ahead and write that in. So we have solid Copper right here. So the anode is always on the far left and the cathode is always on the far right, and so it's easy to remember that because "A" comes before "C" in the alphabet, so the anode comes on the left side and the cathode comes on the right side. And again, this is just the shorthand way of representing a Cell, so instead of drawing this huge picture if you see this written, if you see all of this written, let me go an underline it here, all this written in the Chemistry textbook, it's just telling you, it's just telling you the same information that's in this picture.