Find molar mass of solute using Π =MRT equation

Calculate the molarity, M, of the solution:
M = Π ÷ RT
Π = 1.78 x 10-3 atm
R = 0.0821 L atm K-1mol-1
T = 25oC = 25 + 273 = 298K
M = 1.78 x 10-3 ÷ 0.0821 x 298 = 7.28 x 10-5mol/L

Calculate the moles, n, of hemoglobin present in solution:
n = M x V
M = 7.28 x 10-5mol/L
V = 100.0mL = 100.0 x 10-3L
n = 7.28 x 10-5 x 100.0 x 10-3 = 7.28 x 10-6mol

Calculate the molecular mass, MM, of the hemoglobin:
MM = mass ÷ n
mass = 0.500g
n = 7.28 ÷ 10-6mol
MM = 0.500 ÷ 7.28 x 10-6 = 68,681 g/mol

Question: 

0.500g hemoglobin was dissolved in enough water to make 100.0mL of solution.At 25oC the osmotic pressure was found to be 1.78 x 10-3 atm.Calculate the molecular mass (formula weight) of the hemoglobin.