Question

An aqueous solution at 27°c contains 3.6 g of a protein in a 200 ml sample. the osmotic pressure is 0.0203 atm. what is the molar mass of the protein

Answer 1

In order to calculate the molar mass of the protein, we may manipulate the ideal gas equation:
PV = nRT, where n is the number of moles. We also know that:
n = m / Mr, where m is mass and Mr is molecular weight
Thus,
Mr = (mRT)/(PV)
Here, the mass is in grams, the temperature is in Kelvin, the pressure is in atm and the volume is in liters, so the molar gas constant is 0.082057.

Mr = (3.6 * 0.082057 * (27 + 273)) / (0.0203 * 0.2)
Mr = 21,828 g/mol
Thus, the Mr of the protein is 2.18 x 10⁴ g/mol