Question

a 250.0 ml sample of an aqueous solution at 25 degrees celsius contains 35.8 mg of an unknown nonelectrolyte compound. If the solution has an osmotic pressure of 11.25 mmHg, what is the molar mass of the unknown compound?

I know you need to have the answer in g/mol. I have grams (0.358 g), but am having a hard time figuring out how to find mols.

Answer 1

pi = MRT. Substitute and solve for M = molarity. Then n = grams/molar mass. You know grams and mols, solve for molar mass. Note that pressure should be in atm for M to be molarity.

Answer 2

So you invert the equation to M=pi/RTi to solve for Molarity. I plug in the numbers ((0.1480 atm)/(0.08206 L atm/K mol)(298K) (1))
That equals 6.1554*10^-4 mols.

Dont you divide 0.358g/6.1554*10^-4??