Question

The elevation in boiling point of a solution $d{T}_b$ is related with molality of solution (m) by the relation:
$d{T}_b=\left[\frac{R{T}_b^2}{\Delta H_{vap}}\right]\left[\frac{M_1}{1+m{M}_1}\right]$, where, $M_1$ is molar mass of solvent and $\Delta H_{vap}$ is heat of vaporisation of solvent. For a dilute solution, the relation ${\left(\frac{\partial T_b}{\partial m}\right)}_{m\to 0}$ gives :

• A. molal ebullioscopic constant
• B. elevation in boiling point
• C. elevation in boiling point $\partial T_b$ becomes more predominant
• D. boiling point of solvent

Answer 1

The correct option is A molal ebullioscopic constant

For a dilute solution, the relation ${\left(\frac{\partial T_b}{\partial m}\right)}_{m\to 0}$ gives molal ebullioscopic constant.

${\left(\frac{\partial T_b}{\partial m}\right)}_{m\to 0}=\frac{R{T}_b^2{M}_1}{\Delta H_{vap}}=K_b$

Ebullioscopic constant: Ebullioscopic constant or Molal elevation constant is the elevation in the boiling point produced when one mole of the solute is dissolved in one kilogram of solvent. Its unit is K kg mol${}^{-1}$.