 Okay, so let's try this one. Osmotic pressure problem, it says a solution is prepared by dissolving 6.00 grams of an unknown non-electrolyte in enough water to make 1.00 liters of solution. The osmotic pressure of this solution is known to be 0.750 ATM at 25 degrees Celsius. What is the molecular weight of the unknown solution? Okay, so in order to do this you're gonna have to remember the osmotic pressure equation, which is pi equals MRT Pi being osmotic pressure, m being molarity, r being the gas constant. Remember that has to be given to you. So r 0.0821 liter ATM per mole Kelvin And this T, remember that's in Kelvin temperature. Okay, so let's change that right away. So this is in Celsius, so we want to do what? 273, right? So that's gonna give us 298 Kelvin. Okay, so let's look at this equation here. What do we not have? Well, we've got osmotic pressure. Right? We've got molarity. No, we don't have that. We've got r and we've got t. So let's solve for molarity. So molarity equals pi divided by RT there. Okay, so effectively now we can plug and chug. Excuse me for this part of the problem. So pi 0.750 ATM divided by 0.0821 liters ATM divided by one mole Kelvin. Multiply that by 298. We like that. So hopefully everybody got to that point. So let's now just cancel out the units that we got. So Kelvin and ATM cancel out and one divided by liters divided by moles is going to be moles per liter, which is molarity units. Okay, so Now let's just get on our calculators and solve this part of the problem. So 0.75 divided by 0.0821 Multiply that by 298 and I get a molarity of 3.07 times 10 to the negative 2 molar or let's just say moles per liter. Okay, so let's just keep it like that. It'll be easier for us. Okay, so it's asking us for the molecular weight. So let's keep that in mind. But in order to find that from these types of units with the mass involved, it's best to find the molar mass first. So what's the molar mass? So we need to look for it. So we've got units in molarity here of moles per liter. Okay And we've got the total volume here. So we should be able to figure out the number of moles of this thing as it. Okay, so the number of moles is going to equal So it's one liter. So it's just going to be 3.07 times 10 to the negative 2 moles for every one liter and well, we've got 1.00 liters of it. So the number of moles of the solute is 3.07 times 10 to the negative 2 moles like that. Okay, so is everybody fine with that? Okay, remember the molar mass is the mass per mole, right, like grams per mole. Okay, so the mass divided by the number of moles. So we have the mass and we have the number of moles. So let's figure out what the molar mass is. So 6.00 grams divided by 3.07 times 10 to the negative 2 moles And that's going to give us units in grams per mole. So to three sig figs I get 196 grams per mole. Okay, but that's the molar mass and it asks us for the molecular weight. So the molar mass is 196 grams per mole. That means the molecular weight is 196 amu. So remember to make that distinction between molar mass and molecular weight. Okay, because this is the mass of one mole of this substance. Okay, that weighs 196 grams, but one molecule weighs 196 amu. Is everybody okay with that? Yes. Questions? Question on that? Okay, I'll hang on. Yeah, sure. Okay, cool.