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Video transcript

I went to Wikipedia and I decided to pick up the definition for an equivalent there and I actually didn't find it too useful but there are some things that I wanted to point out so it says the equivalent is formally defined as the amount of a substance which will either react or supply with one mole of hydrogen ions and acid-base reaction or do the same with one mole of electrons in a redox reaction so so all I've really figured out so far I was a little confused when I read this but I figured out what they're saying is that an equivalent is basically some amount some number right so let's start there so when someone says hey how many equivalence do you have I know that they're talking about some number so equivalent is equal to and this is for some ion right so so for some ion of my choosing an equivalent equals some number and and usually that number is in terms of moles so some number of moles that I need so needed to balance something some I'm actually balancing some charge so balance the charge of an oppositely charged so an opposite charge opposite mono valent actually I should even add balanced charge of I guess I can add it without erasing charge of one mole that's actually really important of an oppositely charged mono valent okay so let's let's jump into an example because I think that will clear up any confusion that you may have to this point so let's say we're talking about for some ion let's say where we pick potassium okay we here's our potassium and I've got to balance out one mole of an oppositely charged mono valent so this is my little line demarking the other side so on the other side let's say we have chloride and chloride is oppositely charged it's negative right and it's a mono valent it's it's not negative 2 or negative 3 it's just negative 1 right so we've got let's say a mole of these because the definition I wrote up just said that I need a mole of an oppositely charging and as I'm writing this up I'm realizing and I hope you are too that there's no way in the world I can write up a mole of this stuff there's no way right so let me just get the point across that just imagine there are a total of this many 6.02 times 10 to the 23rd chlorides because that's really the question how many potassium do need to balance out the charge from all of those chlorides and that's too big a number too big a number to write out in any easy way other than to say well maybe you need some number of moles of potassium and that's why I wrote that right into the definition so so let's figure this out so we know that potassium binds one to one with chloride right we know that's what happens so when potassium is floating around and it's going to bump in a chloride it's going to go 1 to 1 so we know that for one chloride we're going to get one potassium and so that means that for one mole of chlorides we're going to get one mole of potassium bound to them right that's going to balance out the charge perfectly so if someone says well how many equivalents do you have for potassium that seems like a very simple answer well you say okay well one equivalent one equivalent would then be one mole of potassium or you could even rephrase it you could say well one mole of potassium and this is how people usually use the phrase they say well one mole of potassium equals one equivalent so I know that's that's the same thing flipped around but that's how people usually state it so now let's do a slightly more challenging example and you'll see where this becomes a little different so instead of potassium let me jump into another one let's do calcium calcium so there's a plus two and same thing as before I'm going to have to choose some on oppositely charged mono valent and I'm going to pick the same one right because this still is oppositely charged I just needed some negative the charged mono valent and chloride suits our purposes we know just as before we need a whole mall of them and so if that's the case how many calcium's will bind or chloride and vice versa many chlorides will bind your calcium so let's imagine we have little chloride and calcium party and they kind of meet each other well what's going to happen is that you're going to have a calcium there and a chloride there and a chloride there right because this will come here this will come here and they're going to basically bind and make this they're going to make cacl2 because the chlorides are only one negative charge oh let me actually this is to negative positive charges I'm flipping around my negatives and positives sorry about that there we go negative negative and plus two so you know that for every one calcium you're going to get two chlorides so let me write that out very clearly so for everyone for everyone calcium or actually I can write for every two chlorides you get one calcium right and that means that for every if I divide both sides by two for every one chloride I basically needed 1/2 a calcium and that's not how we think about it usually because it's hard to imagine 1/2 a calcium but at least the math works out there and so if I'm talking about one mole of chloride one mole of chloride then I'm left saying well then I have a half a mole of calcium so far so good and so then one equivalent going back to our definition equals one half mole of calcium and I said that we could flip around the equation and we can we could say well then one mole now all I did is multiplied both sides by two one mole of calcium oh I'm not writing clearly right now sorry one mole of calcium equals two equivalents so there is how people usually phrase it they'll say okay well how many equivalents do you get for one mole of something and so here you would say the answer is two and so I just want to point out something to which is that we kind of did this a long way but here is a quick and dirty way you could say well I know that calcium is divalent and we know that potassium was mono valent and here is kind of an interesting pattern that's emerging right like as the ca plus two emerge we got two equivalents out of it let's test this with us third one let's just see what we get if we use let's say nitrogen so let's do nitrogen nitrogen is negative three and I have to create my boundary and on the other side I need some oppositely charged mono valent so there's a mono valent and its opposite here's mono valent check and it's oppositely charged check opposite opposite of the negative right so check check it meets our requirements and I need a mole of them so I have to draw out a mole and you know there's no way I can do that as I said before and so just imagine one mole of these guys and the question again is how much nitrogen do I need to balance all this out and I'm going to just underlined in red the the clue so here's the clue and let's now actually go through the steps of figuring it out kind of longer way so let's imagine you have a nitrogen here negative three and it's going to be at this it's a cocktail party and meet some protons and in this case three of them come by so it's going to form nh3 right and a ch3 if we say three protons then come together with one nitrogen which is what we just said then I can divide both sides by three and I can see that one proton then comes with one-third of a nitrogen so far so good and I can then even go on to say one mole of protons which is going back to our definition would be balanced out by one-third of a mole of nitrogen and if that's the case and I can say well one equivalent equals 1/3 of a mole of nitrogen and I'm going to flip this around just as we did before I could say then one let me change that I could say then one mole of nitrogen equals three equivalents and remember we underlined that little three in the beginning and I'm going to underline it again and now you can very clearly see the pattern that's emerging so you can see that anytime you look at the cation or anion that you're talking about if you look at the number like if it's a magnesium that's 2 + or calcium is 2 + then you can then you can know immediately that that probably means that if you did the the work the long way like we just did that the equivalents are going to work out to the same number so nitrogen has three equivalents magnesium or calcium of two equivalents and potassium and chloride they all have one equivalent so that's what equivalents mean in terms of the moles needed to balance out charge on the opposite side