Question

Calculate the approximate $\Delta \,T_{b}$ (in $\left.K \right)$ for $0.001$ molal $KCl$ solution, if its van't-Hoff factor is $1.98\left[K_{b}\right.$ of water is $\left.0.52 \,K\, kg\, mol ^{-1}\right]$

• A. $1.03$
• B. $1.03 \times 10^{-3}$
• C. $1.03 \times 10^{-5}$
• D. $1.03 \times 10^{-1}$

Answer 1

Answer: (B)

We know that

$\Delta\, T_{b}=i K_{b} m $

$\left(\because \Delta T_{b}=i . K_{b} \times m\right)$

where, $\Delta \,T_{b}=$ elivation in boiling point (to time)

$ i $ = van' t - Hoff factor (1.98)

$K_{b} $ = molal elevation constant $(0.52) $

$ m $ = molality $(0.001\, m ) $

$ \Delta\,T_{b} =1.98 \times 0.52 \times 0.001=0.0010296 $

$ \Delta \,T_{h} =1.03 \times 10^{-3} $