 Okay. So, ethyl alcohol is prepared industrial by the reaction of ethylene C2H4 with water. What is the percent yield of the reaction if 4.6 grams of ethylene gives 4.7 grams of ethyl alcohol? So the reaction equation is written right here, okay, and the masses are given right here. So, recall percent yield is one over the other times 100, right? It's a portion over the total times 100. And here you may think that you're going to take one of these masses divided by the other mass and multiply it by 100. But that, if you do that, you forget that these two molecules weigh different amounts, okay? So if you remember, you have to do it by numbers. And in chemistry, numbers is moles. So you're going to have to convert these things to moles first, okay? So in order to do that, right, you're going to have to figure out what is the molar mass of these two things, okay? So let's do that first. I'm just going to do it on the calculator. The next step is to convert each of these to the number of moles, okay? So let's just, for a space filler, put the actual substance. 4.6 grams of ethylene, right? And we want moles of ethylene. Just using that as the space holder for you guys, okay? So the number of, well, better right here, okay? So remember, like we were saying, percent whatever, percent anything, is number of the, what you got, our portion, divided by number of total times 100%, okay? So the total here is what we started out with, okay? So we started out with 0.16 moles of the reactant that we're interested in, right? And we ended up with 0.10 moles of product, okay? Does everybody understand where I'm going with this? So what we're going to end up doing is taking the product, dividing it by the total number of moles of reactant, and multiplying that by 100%. Okay, so let's just do that formally. If it were a maximum yield reaction, right? Maximum or 100% yield, you would have gotten 0.16 moles of ethanol out of this thing. Does everybody understand where we're going with that? Right? Because why is that? Because we have a 1 to 1 mole ratio here, okay? So, anyways, so let's calculate the percent yield. The yield that we got, right? Which was 0.10 moles divided by the yield that we should have gotten. I'm just using the numbers that are still in my calculator. So if you just put 0.1 and 0.16, you might get a slight... But to 2 sig figs, I got 62%. I think that usually you just want whatever... Well, yeah. I mean, well, the thing is, is if you didn't, you would get a percent yield that was bigger than 100%, which doesn't make any sense. But in the lab, you know, you could do something wrong. Like in the experiment that we did this last week, you know, we didn't let it dry for very long, you know? So a lot of that weight on like your copper or whatever is going to be from water, okay? So you may get a percent yield that is bigger than 100%. So don't just be like, this one's smaller than this one. Plop them in there, you know what I'm saying? You got to think about your reaction equation, right? Because it doesn't... What you want to remember is that you're calculating your percent yield of your product, okay? It doesn't mean anything to say percent yield is nonsense to say percent yield of your reactions, okay? So... You can't ever have more than 100% yield, right? I mean, that's what we were just saying. It doesn't make sense to, but oftentimes in the lab, especially in our undergraduate GenCAM labs, we won't dry the product for long enough or something, you know, you guys may leave your store bar in there and weigh it or something like that and be like, I got a 5000% yield or something like that, okay? But... So, what I'm really saying is... Yeah, it doesn't make sense to, but don't manipulate your numbers, especially in lab, you know, to make it to be under 100%, okay? I'd prefer you to, in lab, describe why you got over 100% yield, okay? Even though it doesn't make sense, right? Questions on that? Yes, so yeah, if you want to think of it that way, it's going to be product moles over total moles times 100%. But, you know, this is the ratio of those moles to moles, too. So you got to watch that, okay? We'll do some more of these when we hit this topic in class, okay?