Homework Help: chemistry

Posted by Wiped Out on Friday, September 14, 2012 at 9:45pm.

A solution was made by dissolving 5.15 mg of hemoglobin in water to give final volume of 1.00 mL. The osmotic pressure of this solution was 1.97 x 10^-3 atm at 25C. Calculate the molar mass of hemoglobin.

pi = iMRT
i = 1 since hemoglobin is nonelectrolyte and doesn't dissociate
T = 298 K
R = constant = .08206 L atm/mol K

1 mL => .00100 L
5.15 mg => .00515 g

I was told that the answer is supposed to be a big number like 64,000. I dont understand how that works. Can someone help me get the right answer?

chemistry - DrBob222, Friday, September 14, 2012 at 9:54pm
pi = MRT
Solve for M in mol/L.
Then M = mols/L. You know M and L, solve for mols.
Finally, mols = g/molar mass and rearrange to molar mass = g/mols. You know grams and you know mol, solve for molar mass. I get close to 64,000 too.
chemistry - Wiped Out, Friday, September 14, 2012 at 10:36pm
oh!!!
chemistry - DrBob222, Friday, September 14, 2012 at 10:40pm
You were making it harder than it is.

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