Question

: The most suitable property for molecular weight determination of polymers is:
A.Osmotic pressure
B.Lowering of vapour pressure
C.Elevation in boiling point
D.Depression in freezing point

Answer 1

To answer this question, you should recall the concept of osmotic pressure as well the basic points of colligative properties with its various examples. The property which works in highly diluted solutions is suitable for determining molecular weight.

Complete step by step answer:
A colligative property is a property of a solution that is dependent on the ratio between the total number of solute particles (in the solution) to the total number of solvent particles. Colligative properties are not dependent on the chemical nature of the solution’s components. Thus, colligative properties can be linked to several quantities that express the concentration of a solution, such as molarity, normality, and molality. The four colligative properties that can be exhibited by a solution are:
Boiling point elevation
Freezing point depression
Relative lowering of vapour pressure
Osmotic pressure
The expression for osmotic pressure can be given by $\Pi = iCRT$ where
$\Pi$ = Osmotic pressure, $i$ = Van’t Hoff Factor, $C$ = concentration, $R$ = Universal gas constant and $T$ = Temperature.
As compared to other colligative properties, its magnitude is large even for very dilute solutions. The technique of osmotic pressure for determination of the molar mass of solutes is particularly useful for biomolecules as they are generally not stable at high temperatures and polymers have poor solubility.

Hence, the correct option is option A.

Note:
The Van’t Hoff factor which is an important aspect of colligative properties is defined as the ratio of the concentration of particles formed when a substance is dissolved to the concentration of the substance by mass. In the case of non-electrolytic substances which do not dissociate in water, the value of $i$ is generally 1. But in the case of ionic substances, due to dissociation, the value of $i$ is equal to the total number of ions present in one formula unit of the substance.