 Okay, so let's do this example problem, and here's the chemical equation. So I've written the chemical equation out for you, but you should be able to do this on your own. If you can't do it, you need to start giving to give, okay? Well anyway, so it says calculate the number of waters of hydration present in a sample of epsom salt or magnesium sulfate, whatever hydrate, given the following data. 1.500 gram sample is heated with stirring until the crystals are reduced to a dry powder. After cooling, the residue was found to weigh 0.8476 grams. So let's write down what the problem is, this is the mass total, and it says the mass of the residue. So what is the residue in this equation? What would be left? The magnesium sulfate, right? So mass of the mag sulfate, we said was 0.8476 grams. Can we figure out the mass of the water from this then? Yes. Okay, so how will we do that? 1.500 grams minus 0.8476 grams. When we do that, it's 524 grams of water. Did we be able to figure out the number of moles of water from that? Yes. Okay, how do we do that? Shut it up. Use the what? Conversion factor. Which is the what? What is the conversion factor we're going to use? We just went over it for an hour, last hour. What is it called, guys? 1.500 grams per mole. What is that called? Molar mass. The molar mass. Molar mass. Okay. So it's water. You guys recall? 1.500 grams per mole. Yes. 1.500 grams of water and on the top, 1 mole of water. Okay. I think it's good to keep that because we're going to have to figure out moles of other things. Yeah. So I get 0.03620 moles of water. Is everybody okay with that? Okay. Also, in this case, because I'm trying to get the ratio of mag-sulfate to water, I need the moles of mag-sulfate, too. Okay? Because remember, this gives us a mole-to-mole ratio, so we've got to figure out that. Is everybody okay with that? Yes. So here, I multiply by the mag-sulfate, and I calculated it earlier, it's 1.2037. So that's just, so when I do that, I get 0.007042 moles of mag-sulfate, magnesium-sulfate. And how do I figure out what X is? I've got to take the moles of this and divide it by the moles of this. Okay? So when I do that, this is actually X over 1, right? This mag-sulfate is just a 1, so it's going to be 0.03620 divided by 0.007042 moles. The moles cancel there, giving us 5.14 to 1 ratio, very close to 5 to 1. Okay? So what you find is that X equals 5. Okay? Everybody okay with that? So we can erase that? Like that. Is everybody okay? So that's how you would do exactly how you would do the second problem. And you're free like, or the third or whatever problem you have.