Question

For a dilute solution having molality m of a given solute in a solvent of molar mass M, b.pt. $T_b$ and heat of vaporisation per mole $\Delta H;{\left[\frac{\partial T_b}{\partial m}\right]}_{m\to 0}$ is equal to :

• A. molal elevation constant of solvent
• B. $\frac{R{T}_b^{2}M}{{\Delta }_{vap}H}$, where M in Kg $mo{l}^{-1};{\Delta }_{vap}H$ and R in $Jmo{l}^{-1}$
• C. $\frac{R{T}_{b}M}{{\Delta }_{vap}S}$, where M in Kg $mo{l}^{-1};{\Delta }_{vap}S$ and R in $Jmo{l}^{-1}$
• D. $\frac{R{T}_b^{2}M}{1000{\Delta }_{vap}H}$, where M in Kg $mo{l}^{-1}$;R and ${\Delta }_{vap}H$ and R in $Jmo{l}^{-1}$ expressed in same unit of heat

Answer 1

Answer: (A), (B), (C), (D)

The correct options are
A $\frac{R{T}_b^{2}M}{{\Delta }_{vap}H}$, where M in Kg $mo{l}^{-1};{\Delta }_{vap}H$ and R in $Jmo{l}^{-1}$
B molal elevation constant of solvent
C $\frac{R{T}_{b}M}{{\Delta }_{vap}S}$, where M in Kg $mo{l}^{-1};{\Delta }_{vap}S$ and R in $Jmo{l}^{-1}$
D $\frac{R{T}_b^{2}M}{1000{\Delta }_{vap}H}$, where M in Kg $mo{l}^{-1}$;R and ${\Delta }_{vap}H$ and R in $Jmo{l}^{-1}$ expressed in same unit of heat

All options are correct.
Molal boiling point elevation constant or ebullioscopic constant of the solvent, is defined as the elevation in boiling point which may theoretically be produced by dissolving one mole of any solute in 1000 g of the solvent.