Question

A liquid possessing which of the following characteristics will be most suitable for determining the molecular mass of a compound by cryoscopic measurements?
(A) That has a low freezing point and small enthalpy of freezing.
(B) That has a high freezing point and small enthalpy of freezing.
(C) Greater than the normal boiling point of either or the liquid.
(D) Smaller than the normal boiling point of either of the liquid.

Answer 1

Hint : The temperature at which a liquid turns into a solid is known as the freezing point. Increased pressure increases the freezing point in the same way as it raises the melting point. In the case of mixtures and some chemical compounds such as fats, the freezing point is lower than the melting point.

Complete Step By Step Answer:
The difference in temperature between the freezing point of the pure liquid and the freezing point of the solution is known as freezing point depression. The improvement in the freezing point for a 1-molal solution of a nonvolatile molecular solute is equal to the molal freezing-point depression constant.
The transition in enthalpy (ΔH) is negative as a fluid transforms from a liquid to a solid state. This is known as the freezing mechanism, and it causes the molecules in the matter to become more organised.
The molal depression in freezing point constant is expressed as ${K_f} = \frac{{R{T_f}^2M}}{{1000\Delta {H_{fus}}}}$
The value of ${K_f}$ would be higher if ${T_f}$ was higher and the enthalpy of fusion of the solid was lower.
As a result, a liquid with a high freezing point and a low freezing enthalpy is best for calculating the molecular mass of a substance using cryoscopic measurements.
Hence, option B is correct (That having high freezing point and small enthalpy of freezing).

Note :
An established constant can be used to quantify an uncertain molar mass using cryoscopy. "Cryoscopy" is a Greek word that means "freezing calculation." Since freezing point depression is a colligative property, ΔT is only affected by the amount of solute particles dissolved, not their composition.