 This is the continuation of our conservation of mass discussion, so in a reaction 36.5 grams of chromium-3 oxide reacts with 13.0 grams of aluminum to produce chromium and aluminum oxide. If 25.0 grams of chromium is produced, what mass of aluminum oxide is produced? Okay, so in order to do this problem, you don't necessarily need to know what chromium-3 oxide and aluminum oxide are. Actually, you can do this problem just using the basis of the conservation of mass that you've already learned. So the reason I've written down chromium, the formula is for chromium-3 oxide, aluminum and chromium is just because I know them. So you could, it's all right down the equation that it says, so it says chromium-3 oxide plus aluminum goes to aluminum oxide plus chromium. And then it gives you masses for these things, so 36.5 grams, 13.0 grams, 25 0.0 grams. And then you're asked, what is the mass of aluminum oxide? So this is just like an algebraic equation. This plus this equals this plus this. Okay, so hopefully you see, we could have called this A, B, C, and D. We didn't need to actually identify what the formulas for those species were. So all we really have to do now is algebraically manipulate in order to solve for X there. Okay, so what can we do? We can say 36.5 plus 13 and then move this over to here and subtract it minus 25, and that's going to give us 24.5 grams of aluminum oxide. So in other words, what do we do if we solve that for X? X equals 36.5 grams plus 13.0 grams. We do that first and then subtract 25.0 grams from that. And what do we get? 24.5 grams. So this is just another example of the conservation of mass law that the law of ZA came up with that we were just talking about. Okay? So if there are any more questions, let me know right now. If not, then we'll kill the video. No? Okay, good.