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March 26, 2017

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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 - ,

    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 - ,

    Post your work and I'll find the error.

  • chemistry - ,

    What do you mean solve for molar mass? I think that is the problem that I am having.

  • chemistry - ,

    nevermind, I got it. Is the answer 160 g/mol?

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