Question

The cryoscopic constant value depends upon?
A. The molar mass of the solute in the solution
B. The molar mass of the solvent in the solution
C. The enthalpy of vaporization of the solvent
D. The freezing point of the solvent

Answer 1

Hint- In order to deal with this question first we will define the term cryoscopic constant then according to its property we will find the factors upon which it depends out of the given four options in the problem.

Complete answer:
Depression at the freezing point describes the process in which adding a solute to a solvent decreases the solvent's freezing point. Depression at the freezing point can be used to calculate the degree of dissociation or the solute molar mass. This type of measurement is called cryoscopy, and is based on accurate measurement of the freezing point.
So, when a mole of non-volatile solvent is dissolved in one kg of solvent, cryoscopic constant is defined as the freezing point depression. The constant in cryoscopy is denoted by ${K_f}$. Depression of the freezing point refers to lowering of the freezing point of solvents as the solutes are applied. It is a colligative property described by the following formula.
$\Delta {T_f} = i \times {K_f} \times m$
Its unit is $K.Kg.mo{l^{ - 1}}$ .
Hence, the cryoscopic constant value depends upon the molar mass of the solute in the solution.

So, the correct answer is option A.

Note- Cryoscopic constant relates the molality in a solution to freezing point depression. A known constant can be used, by cryoscopy, to measure an approximate molar mass. Depression at freezing point is a colligative phenomenon, and the temperature difference depends only on the number of dissolved solvent particles, not on the composition of those particles. Cryoscopy is associated with ebullioscopy which determines the same value from the ebullioscopic constant (the elevation of the boiling point).