Question

What is molal elevation constant? Drive its equation and give its unit.

Answer 1

The molal elevation constant is the elevation in the boiling point of a solvent when one mole of a non-volatile solute is dissolved in it per kilogram of solvent.

The unit of molal elevation constant is given as $Kkgmo{l}^{-1}$.

Derivation:

Experimentally, it has been shown that the elevation of the boiling point $\left(\Delta T_b\right)$ for dilute solutions is directly proportional to the molal concentration of solute in the solution. Therefore, we can write:

$\Delta T_b\propto m$

$\Delta T_b=K_{b}m$

Here, $m$ is molality or the number of moles of the solute dissolved in a kg of solvent. $K_b$ is the molal elevation constant.