Homework Help: chemistry

Posted by Bru on Tuesday, October 2, 2012 at 9:19pm.

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?

a.) 237 g/mol
b.) 484 g/mol
c.) 351 g/mol
d.) 699 g/mol
e.) 160 g/mol

I thought I did the math right, but I guess I didnt, because I just cant seem to get the right answer. Help me please?

chemistry - DrBob222, Tuesday, October 2, 2012 at 10:53pm
pi = MRT
Solve for M
Then M = mols/L, solve for mols.
Then mols = grams/molar mass; solve for molar mass.
Don't forget pi is in atm so that's 11.25/760 = ?atm.
Also T is in K = 298 K and
R is 0.08206. I ran through it and obtained one of the answer choices.
chemistry - DrBob222, Tuesday, October 2, 2012 at 10:54pm
Post your work and I'll find the error.
chemistry - Bru, Wednesday, October 3, 2012 at 9:11pm
What do you mean solve for molar mass? I think that is the problem that I am having.
chemistry - Bru, Wednesday, October 3, 2012 at 9:22pm
nevermind, I got it. Is the answer 160 g/mol?

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