 So, this one says an old bottle was found in the laboratory. The handwritten label says that it is copper 2-sulfate pentahydrate, a 3.000 gram sample of the bright blue substance is strongly heated until a constant weight is obtained. The pale gray-white residue is found to weigh 1.6762 grams. What is the actual formula of the copper 2-sulfate pentahydrate? Okay, so this is what is on the label, okay, but it's not actually this particle, or this formula unit, does everybody understand that? So, in fact, what it's saying is that this number is probably not correct, and it wants you to figure out what that number is. So, in other words, is everybody okay with that? So, let's just write the chemical equation here, the chemical equation that would occur, or the chemical reaction, if you will, that would occur, or the phase change that would occur, if you heated this substance up, right? So, what we're really looking at for is the coefficient here, or the ratio of moles here to moles here. Is everybody okay with that idea? Okay, so, anyways, in other words, it's telling us once we, this mass of this sample is this, actually, we can write CUSO4XH2O, okay, that's the sample, the residue is actually CUSO4 itself, okay? So, the mass difference would be the mass of water, actually, right? Why? Because of the law of conservation of mass, right? The same mass has to be on this side, this has to be on this side. So, if we have this starting out, and this ending up, this is gone, right? So, the mass of water, we can figure that out. It's going to be the, of course, the mass of CUSO4XH2O, CUSO4. We need to figure out the number of moles of each of these things. So, we calculated the molar mass of CUSO4 previously, and it's 159.56 grams of CUSO4, copper 2 sulfate, or 1 mole of copper 2 sulfate. So, why did I do that? So, I can get the number of moles in the same thing here. I actually calculated the molar mass. Okay, so, now let's just go ahead and do these two problems. So, since I have that number, let's just do the bottom one. We have this stuff, so, well, I'm going to be on top, okay, because we want these to be integers, of course, zero. Okay, so, it's a seven to one ratio. So, what this is saying is that X is seven. So, what's the formula of four? So, it's effectively calculating the, just like calculating the empirical formula. Okay, what's that? Whenever you do the ratio of those, how do you know which one goes on top later? Well, like I was saying, if we put the other one on top, if we did it the other way, it would be a number less than one. I mean, it doesn't make sense to put numbers less than one in the chemical equation. Does that answer your question? Same thing with the empirical formula. It doesn't make sense to have numbers that are non-anagers in the subscripts. So, if you want to compare that with this. Any other questions with this? Okay, you guys all know how to do this one. Okay, and you knew how to do it before, but you definitely know how to do it.