Question

Camphor is often used in molecular mass determination because :
A. it is readily available
B. it has very high cryoscopic constant
C. it is volatile
D. it is a solvent for organic substances

Answer 1

Hint : We have studied in thermodynamics that cryoscopic constant is related to the molality to freezing point depression. Freezing point depression is related to lowering of freezing point of solvents in addition to solutes. It can be described with the help of Raoult's law. In cryoscopic, a known constant is used to determine an unknown molar mass.

Complete step by step solution:
We know that camphor is a flammable, waxy solid which possesses strong aroma. It has a molecular formula ${C_{10}}{H_{16}}O$. Camphor is used as a solvent in determination of non-volatile solute. Melting point of camphor is high. The value of the cryoscopic constant of camphor is almost twenty times more than the cryoscopic constant of water. According to Raoult's law, $\Delta T = m \times {K_f}$ where $m$ is molality and ${K_f}$ is cryoscopic constant. If camphor will have a high cryoscopic constant then depression in the freezing point will be more. Hence the accuracy in measurement of molecular mass will be more. ${K_f}$ depends on the nature of the solvent. Hence camphor is used in molecular mass determination because it has a very high cryoscopic constant.

So option B is the correct answer to this question.

Note : Depression in freezing point is a colligative property. We got the information that when a non-volatile solute is added to a volatile solvent then decrease in vapour pressure of solution is observed. This decrease in vapour pressure is used to determine several properties of the liquid solution. These properties depend on solute particles of the solution and are known as colligative properties. Hence camphor is often used in molecular mass determination because it has a very high cryoscopic constant.