 So a problem like this is very similar to an empirical formula problem. Let's try it. It says a 3.10 gram sample of anhydrous nickel 2 sulfate was exposed to moist air. If 5.62 grams of a hydrate of nickel 2 sulfate was obtained, what is the formula of the hydrate? So in order to do this, we have to understand that anhydrous nickel 2 sulfate means nickel 2 sulfate without the water associated with it. And it's going to make the hydrate as the product. So I'm going to have something like that. Plus x amount of water goes to nickel 2 sulfate x H2O sulfate. Does everybody understand that that's the equation that we're going to be working with? So, well, what do we need to do? We need to figure out how many moles of nickel 2 sulfate we've got to start out with. So I calculated the molar mass of this earlier. What did we get? 15473. So 154573, we'll cancel that out. 0.0200 moles of nickel 2 sulfate. So the mass of the hydrate is 5.62 grams. The mass of the nickel 2 sulfate is 3.10 grams. We should be able to figure out what the mass of the water is from those two numbers. So the mass of the water is going to be, well, 5.62 grams minus 3.10 grams, 2.52 grams of water. Remember, the molecular or the chemical equation gives us the mole to mole ratio, not the mass to mass ratio. So what do we have to do to this number? Convert it to moles. So you remember the molar mass of water for 0 moles of water. Is everybody OK with that? So now, remember, we're looking for, well, what's this formula? So we know most of it. We just don't know x here. Does everybody understand that? So what do we have to do? Well, we're going to, x is going to be bigger than 1, right? So we're going to have to figure out the mole ratio. So the number of moles of nickel 2 sulfate is going to be 0.0200 divided by 0.0200 nickel 2 sulfate 2, well, what do we got? 0.140 divided by 0.0200 H2O, like that. So very similar to doing the empirical formula, except in this case, we're figuring out coefficients. So when we do that, when we divide 0.02 divided by 0.02, that gives us 1, right? The other one is, well, we don't even have to do it. It's 7, all right? So is everybody OK with that? So what would our formula be? Nickel 2 sulfate heptahydrate, for niso4.7 H2O. And if we wanted to name it, it would be nickel 2 sulfate heptahydrate. Why would I say, why do I keep saying nickel 2? Because nickel is a transition metal. So we have to remember, say, nickel 2. So let's just write out the name of this thing. So 2 sulfate. So the 2 is because nickel's a transition metal. Heptah means 7. Hydrate means 1. Any questions on doing something like this? So I know we've been doing things like this for a long time. I think this was chapter 3 or chapter 4 material. And I know we've done a few of these in the lab, so.