Learn about Senior Chemistry, Redox 1, in this comprehensive video by bannanaiscool.
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Male Speaker: Welcome to oxidation and reduction. Here is a little demo, a solution of zinc nitrate, a solution of copper 2 nitrate, piece of copper, piece of zinc. Take the copper, put it into the zinc nitrate, look at it, nothing happens. You put it into the copper 2 nitrate, that's a pretty clean piece of copper. Take a piece of zinc, put it into the zinc nitrate solution, there is no reaction. Put it into the copper 2 nitrate, oh that don't take very long at all does it and look at that and there is a reaction where the zinc metal is breaking down into zinc ions and copper ions are forming copper metal on here, it pretty dark now but that's solid copper forming. So many of the reactions that take place on this planet involve the exchange of electrons from one substance to another even the majority of the reactions that we have in the last unit, certainly all the combustion reactions that we did in the energetics unit where all exchanges of electrons, so even though explosions might happen in a vigorous reaction occurs that's usually the result of exchanges of electrons between elements. Now exchanges of electrons this gives us the redox unit that we are doing right now or electrochemistry because that exchange of electrons causes a current to be able to be form because electrons are electricity, so this is what we are studying here and the redox term means reduction, oxidation, so the copper, zinc demonstration that you just saw I will explain right now in terms of the equations behind it and what was happening underneath the surface of this piece. Okay, so what we saw was that the zinc metal was turning into zinc ions and breaking down while the copper in solution receive two positives ions in solution were actually forming solid copper. There were two things that were going on there. The zinc is breaking down into zinc ions and giving up two electrons, so you see how that's balanced, two positives and two negatives, zero total on this side, zero here and that's called a half reaction. Two half reactions together make up a whole reaction, so the other part of that was that the copper ions were gaining those two electrons, right there to form solid copper, so these two reactions together make a net equation, okay, now there are some terms and definitions that are absolutely vital and you got to understand you have to memorize them you really do because a lot of the test that teachers do is just test only on the terminology here. So, when a substance goes from being a metal or a certain chemical and breaks down to form electrons that's called oxidation. Oxidation means losing electrons and losing electrons means if the substance has the electrons written on the right hand side of the equation. Zinc is being oxidized, it's losing two electrons. Now, if the copper irons here are gaining two electrons, so the copper iron is undergoing reduction, reduction means gaining electrons and I know this sounds cookie because you say reducing means gaining and don't make sense but then again chemistry don't make sense, so that we have perfectly good sense but what it really means is this, see that charge of two positive there is turning into a charge of zero for Copper. Two positive is going down, it's being reduced to zero and therefore gaining electrons reduces a charge, so that's why it's called reduction. Okay, so we have got oxidation reduction and we can't add two equations together that both are reduction or both oxidation. This unit isn't red, red and it's not OX, OX, it's reox, reduction and oxidation, so one is always loosing, the other ones always gaining, that make sense. Now if this loses two electrons and this gains two electrons the ratio of reaction between them is like one-to-one here and so we take this reaction and this reaction add them together, when you add them together you do realize of course that the electrons cancel out, so you get this and this reacts to form this and this and that is the net ionic equation f