Question

The use of common salts eg. ${\text{NaCl}}$ or ${\mathbf{CaC}}{{\mathbf{l}}_{\mathbf{2}}}$ ​ anhydrous, is made to clear snow on the roads. This causes:
A.A lowering in freezing point of water
B.A lowering in the melting point of water
C.Ice melts at the temperature of atmosphere present at that time
D.All of the above

Answer 1

To answer this question, you should recall the concept of colligative properties. Lowering of the freezing point is a colligative property. The freezing point of a solvent decreases in addition to solute.

Complete step by step answer:
We know that the term Freezing point depression refers to the lowering of the freezing point of solvents upon the addition of solutes. Colligative properties depend on the presence of dissolved particles and their number but not on the identity of the dissolved particles.
The depression in the freezing point of a solution can be described by the following formula:
$\Delta {{\text{T}}_{\text{f}}}{\text{}} = \;{{\text{K}}_{\text{f}}}\; \times \;{\text{b}} \times \,{\text{i}}$ where: $\Delta {{\text{T}}_{\text{F}}}$ is the freezing-point depression, ${{\text{K}}_{\text{f}}}{\text{}}$ is cryoscopic constant, ${\text{b}}$ is the molality and ${\text{i}}$ is the van 't Hoff factor.
At the freezing point of any solvent, there always exists an equilibrium between the different states i.e. liquid state and the solid-state of the solvent. At this equilibrium point, vapour pressures of both the liquid and the solid phase are equal. Upon the addition of a non-volatile solute, the vapour pressure of the solution is found to be lower than the vapour pressure of the pure solvent. This causes the solid and the solution to reach equilibrium at lower temperatures.
Hence, the correct option is option D.

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 ${\text{i}}$ is generally 1. But in the case of ionic substances, due to dissociation, the value of ${\text{i}}$ is equal to the total number of ions present in one formula unit of the substance.