Camphor is often used in molecular mass determination because :-
A
It has a very high cryoscopic constant
B
It is volatile
C
It is solvent for organic substances
D
It is readily available
The answer is A.
Solution
Depression in freezing point: $\Delta T_f = K_f \times m$, where $K_f$ is the cryoscopic constant and m the molality. For camphor $K_f \approx 40$ K kg mol$^{-1}$, which is very high compared with water (1.86 K kg mol$^{-1}$) or benzene (5.12 K kg mol$^{-1}$). Because $K_f$ is so large, even a small amount of solute gives a large, easily measured depression of the freezing point. An ordinary thermometer is then enough. This is the basis of Rast's camphor method for finding molar masses of organic compounds. So camphor is used because it has a very high cryoscopic constant.
ConceptUse of camphor in Rast's method
Solutions in past papers
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