posted by RE .
A solution containing 26.40 mg of an unknown protein per 22.5 mL solution was found to have an osmotic pressure of 3.95 torr at 21 C. What is the molar mass of the protein?
Pi = MRT
You know Pi (osmotic pressure) which you want to convert to atmospheres. Use 0.08205 for R and convert T to Kelvin. Calculate M, molarity.
Then M = moles/L which allows you to calculate # moles.
Finally, # moles = g/molar mass which allows you to calculate molar mass. Post your work, preferably with the problem, on a new post, if you run into trouble.