Final answer:
Osmotic pressure can be used to measure the molecular weight of protein molecules by using the colligative property that is directly proportional to the number of solute particles, which can be used to calculate the molar mass of the protein.
Step-by-step explanation:
We can use osmotic pressure to measure the molecular weight of protein molecules by correlating osmotic pressure with colligative properties. Osmotic pressure is directly proportional to the concentration of solute molecules in a solution and can be described with an equation similar to the ideal gas law. To measure the molecular weight of a protein, a known mass of the protein is dissolved in a solvent to create a solution. When this solution is placed in a device with a semipermeable membrane, the osmotic pressure can be measured by determining the external pressure required to halt the net flow of solvent molecules into the solution.
This method relies on the fact that osmotic pressure is influenced by the number of solute particles in a solution, which is in turn dependent on the number of molecules of the dissolved substance. For non-electrolytes like glucose or proteins that do not dissociate into ions, the number of particles is equal to the number of molecules. By using the osmotic pressure data, along with the known mass of the protein and the volume of the solution, one can calculate the molar mass, and thus the molecular weight of the protein.