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

The correct option is A

The molar mass of the solute in the solution

The explanation for the correct option:

Option (a) The molar mass of the solute in the solution

• A cryoscopic constant is defined as the freezing point depression caused by dissolving one mole of a nonvolatile solute in one kilogram of solvent.
• The cryoscopic constant is indicated by the symbol ${\mathrm{K}}_{\mathrm{f}}$ .
• The lowering of the freezing point of solvents due to the addition of solutes is referred to as freezing point depression.
• The following formula describes a colligative feature.

${\mathrm{\Delta T}}_{\mathrm{f}}=\mathrm{i}\times {\mathrm{K}}_{\mathrm{f}}\times \mathrm{m}$

• It is measured in $\mathrm{K}\mathrm{kg}{\mathrm{mol}}^{-1}$.
• It is determined by the solute's molar mass in the solution.

The explanation for incorrect options:

Option (b) The molar mass of the solvent in the solution

• This option is incorrect as the cryoscopic constant is determined by the molar mass of solute and solvent.
• As it includes Molality, which is a measure of the number of moles of solute in a solution corresponding to $1000\mathrm{g}$ of solvent.

Option (c) The enthalpy of vaporization of the solvent

• This option is incorrect.
• As the cryoscopic constant does not depend on the enthalpy of vaporization of the solvent

Option (d) The freezing point of the solvent

• It depends on $∆{\mathrm{T}}_{\mathrm{f}}$, which is depression in the freezing point and not the freezing point of the solvent.
• So, this option is also incorrect.

Hence, the cryoscopic constant value depends upon the molar mass of the solute in the solution, option (A) is the correct answer.