Question

Give reason for the following.
Measurement of osmotic pressure method is preferred for the determination of molar masses of macromolecules such as proteins and polymers.

Answer 1

Osmotic pressure is the minimum pressure applied to a solution to prevent the inward flow of its pure solvent across a semipermeable membrane. In this method pressure is measured at room temperature.

Complete step by step answer:
Osmosis is the spontaneous movement of solvent molecules through a selectively permeable membrane into a region of higher solute concentration. Osmotic pressure is defined as the external pressure applied so that there is no net movement of solvent across the membrane. Osmotic pressure is a colligative property which depends on the molar concentration of the solute but not on its identity. In biological systems, the solvent present in osmosis is generally water but it can occur in other liquids, supercritical liquids and even gases.
Measurement of osmotic pressure method is preferred for the determination of molar masses of macromolecules such as proteins and polymers. This is due to the following two reasons.
- The values given by the other colligative properties (elevation in the boiling point, the depression in the freezing point and relative lowering of vapour pressure) are so low that they cannot be measured accurately.
-Measurement of osmotic pressure is carried out at room temperature which does not require heating. Heating may change the nature of the polymer.

Note: Osmotic pressure is defined as the external pressure applied so that there is no net movement of solvent across the membrane. Osmotic pressure is a colligative property like elevation in boiling point, depression in freezing point and relative lowering of vapour pressure but these properties other than osmotic pressure have very low value and need some heating.