Question

If $1g$ of solute (molar mass $=50g$ ${mol}^{-1}$) is dissolved in $50g$ of solvent and the elevation in boiling point is $1K$. The molar boiling constant of the solvent is?

• A. $2$
• B. $3$
• C. $2.5$
• D. $5$

Answer 1

The correct option is C $2.5$

${\Delta T}_b=K_b\times$ molality

${\Delta T}_b=1K$

Molality $=\frac{moles\left(n\right)}{weightofsolvent\left(Kg\right)}$

Molality $=\frac{1\times 1000}{50\times 50}=\frac{10}{25}=\frac{2}{5}$

${\Delta T}_b=K_b\times$ molality

$1=K_b\times \frac{2}{5}$

$K_b=2.5$ $K$ $Kg$ ${mol}^{-1}$