 So how would we prepare one liter of a three molar citric acid solution? So it tells you the molecular makeup of citric acid. We have six carbons, eight hydrogens, and seven oxygens. Oxygen is 15.999. Take a look. Hydrogen is 1.00. And I'm going to round this to 8, 1.008, because I'm just going to use three decimal points. And carbon is 12.001. It's actually 12.011. Sorry. So then again, we're going to have to multiply this times six, this times eight, and this times seven. So 12.011 times six, 72.066. Eight times 1.008.064. 15.999 times seven. It's 111.993. We're going to add those together, and we're going to get 192.123 grams per mole. Now, we know that 192.123 grams is in one mole, and we need three moles per one liter. The moles are going to cancel, but we'll multiply this out. And we'll have 192 plus, oops, one, two, three, times three, 576.369 grams per one liter. And so again, we're going to dissolve 576.369 C6H807 in water and bring to the volume of one liter. So this one's a little bit more complicated because we're not just doing one liter of solution, but how would you prepare 500 milliliters of three molar aqueous solution of sodium carbonate? So there's two sodium atoms. There's one carbon atom, and there are three oxygen atoms. 0.011 in our sodium. I'll look again. 22.990. We're going to multiply that one by two, that one by one, this one by three. 47.997.011. 45.980. And we will add those together. And we're going to have 105.998 grams per mole for sodium carbonate. So we need 500 ml of a three molar aqueous solution. So we know we have 105.998 grams in one mole. We need three moles per one liter. But since we're going to be dealing with milliliters and we know that one liter equals 1,000 milliliters, I'm just going to go ahead and put that in our equation here to replace one liter with 1,000 milliliters because that will make it easier for us to solve. So we know that the moles are going to cancel. We are going to use three, divide it by 1,000. Actually, let's go back. I don't want to divide that by 1,000 quite yet. We just want to do 105.998 times three. And we'll have 317.994 grams per 1,000 milliliters because that is what's going to allow us to set up our proportion. So we're going to set up our proportion at that point, 994 grams per 1,000 milliliters. And we need to know how much per 500 milliliters. And so we'll solve for x by multiplying by 500 milliliters on both sides. Those will cancel. Those can cancel and leave this with a 2. And what we'll have is 317.994 is 158.982 grams per 500 milliliters. And so you'll dissolve 158.982 grams in water and bring to volume 500 mL. There is another way we can do this problem. We can know that we have 105.998 grams per mole. And we can go over here and know that 3 moles per liter equals how many moles per 500 mL. And so we can say that 3 moles per 1,000 mL equals x per 500 mL. And again, multiply both sides by 500 mL. Those cancel. And what you're going to get is x equals 1.5 moles. So then you would know that what you needed to do is have 105.998 grams per mole times 1.5 moles. And you're going to get that same 158.982 grams that you need to dissolve and bring to the volume of 500 mL. So you can solve it either way and either way is fine. It's just whatever makes the most sense to you if you want to figure out the number of moles you're looking for or the number of grams first.