If 6.38 g of a polyethylene glycol is dissolved in 7550 ml of water at 300 oK, the solution has an osmotic pressure of 0.171 torr. Calculate the molar mass (g/mol) of the polyethylene glycol.

Answer 1

pi = nRT
You know pi, R, and T (By the way, the new rules state that the degree sign is NOT used with Kelvin; i.e., you would write 300 Kelvin although 300^o C is correct). Solve for n, then n = grams/molar mass to calculate molar mass.

Answer 2

pi* = MRT
slight typo here. M and not n.
M = molarity = moles/L. You have L and M, calculate moles. Then moles = grams/molar mass. Sorry 'bout that.