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.

Question

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 don't understand how that works. Can someone help me get the right answer?

Answer 1

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.

Answer 2

You were making it harder than it is.

Answer 3

@DrBob222
Nothing is easy without dedication and hard-work. Just because you are a doctor, does not make this easy