 Let's try this problem. This one does number 9 on exam 2b. What is the mass of copper 2 sulfate needed to make 4.230 milliliters of 15.00 molar aqueous solution? The first thing you need to know about this problem is the formula of copper 2 sulfate. If you can't do that, then you're out of luck for this formula mostly. So copper, if you look at the periodic table, it's Cu, right? And it says it's 2 plus, right? Because it says it's copper 2. So that tells you it's 2 plus. So we've got copper 2 plus. And sulfate is SO4, and you just know this from the table that you memorized. It's SO4 2 minus. So that's sulfate. So when we combine those two together, it will be just being 1 to 1 because 2 plus 2 and minus 2 cancel each other out. So our formula is going to be CuSO4. So this is asking us what's the mass of it needed to make 4.230 milliliters of the 15 molar solution. So we need to know the equation for molarity, which is molarity equals the number of moles of solute divided by the volume in liters, okay? So let's figure out if we know these things. So number of moles of solute, well we know the volume in milliliters, it's 4.230. To get that to liters is to convert to a liter. So we've got 1 liter close to a user calculator to get 0.0015. And we should be able to figure out the number of moles of solute, okay? So the number of moles of solute here is this right there, okay? So we've got to get that by itself. So we've got to get VL out of that. We've got to move it to the other side. So multiply both sides by VL. That cancels out on that side and VL over there, okay? So we've got now N's VL times molarity, okay? So we just take these two numbers, 15, 2, 3, 0, 0, 3, 4, 5, 10 to the magnitude, 0, 6, 0, 3, 4, 5. Okay, so that's how many moles of copper-salt we have. So now, so let's, can I erase this focus? Okay, so the molecular weight of CuS of 4, what is that? Okay, so we've got Cu1S104. Now I gave you particular numbers that you don't want to do to you. So let's go ahead and erase those numbers. So Cu is 6, 3, 0, 5, 5, S is 0, 7 is 16, 0, 0, AMU. So 16 times 4, yeah, that's 159.62 AMU or that's the, that's the formula weight or the molecular weight, okay? Yeah, the molar mass, this is 159.62 grams per one mole. So all we've got to do now is take this number and multiply it by that number and it will give us the mass. Can I erase that from here again? Two grams for one mole. This is 10.13.