Asked by Luke

A saturated solution is made by dissolving 0.325 g of a polypeptide (a substance formed by joining together in a chainlike fashion some number of amino acids) in water to give 1.37 L of solution. The solution has an osmotic pressure of 4.13 torr at 28 °C. What is the approximate molecular mass of the polypeptide? g/mol

Answers

Answered by DrBob222
pi = MRT
pi = 4.13 torr/760 = ? atm
M = unknown
R = 0.08205
T = 28 + 273 = ?
Solve for M in mols/L
You know M and L, solve for mols.
Then mol = grams/molar mass. Youj know grams and mols, solve for molar mass.

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Answered by Luke
So would you do M=RT/Pi
M=(301 x .08205)/.005
4939.41?
Answered by DrBob222
No, if pi = MRT then M = pi/RT
M = 0.00543/(0.08205*301) = about 0.000220M or mols/L.
M = mols/L
mols = M x L = 0.000220*1.37L = about 0.000301

mols = grams/molar mass or
molar mass = grams/mols = 0.325/0.000301 = ?
Note, however, that even if what you proposed were correct that you threw away two perfectly good numbers with that 0.005.
4.13/760 = 0.00543
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