Question

Which of the following is correct?
Here,
$K_f\text{is cryoscopic constant}$
$T_f\text{is F.P. of pure solvent}$
$M\text{is the molar mass of solvent}$
$\Delta H_{fus}\text{is the molar enthalpy of fusion of the solvent}$
All quantities are in SI units

• A. $K_f=\frac{R\times T_f^2\times M}{1000\times \Delta H_{fus}}$
• B. $K_f=\frac{2R\times T_f\times M}{1000\times L_{fus}}$
• C. $K_f$ value is dependent on the nature of the solute.
• D. None of the above

Answer 1

The correct option is A $K_f=\frac{R\times T_f^2\times M}{1000\times \Delta H_{fus}}$

Depression in Freezing Point is a colligative property. It is dependent on solute concentration and not its nature.


Cryoscopic constant is the depression in freezing point when the molality of solution is unity.


$K_f=\frac{R\times T_f^2\times M}{1000\times \Delta H_{fus}}=\frac{R\times T_f^2}{1000\times L_{fus}}$

$L_{fus}\text{is the latent heat of fusion of the solvent per g}$


$\text{Unit of Cryoscopic constant is}Kkgmo{l}^{-1}$