Question

A solution containing $2.5 \times 10^{-3} \, kg$ of a solute dissolved in $75 \times 10^{-3} kg$ of water boils at $373.535 \, K$. The molar mass of the solute is ___$g\, mol ^{-1}$. [nearest integer] (Given: $K _{ b }\left( H _{2} O \right)=0.52\, K\, Kg\, mol ^{-1}$, boiling point of water $=373.15\, K$ )

Answer 1

$W =2.5\, g $
$ K _{ b }=0.52 $
$ W _{\text {solvent }}=75 g $
$ M =$ Mol. Wt. of solute
$ T _{ B }^{\prime}=373.535 \,K $
$ T _{ B }^{ o }=373.15\, K$
$ \Delta T _{ B }=0.385= K _{ b } $ molality
$ 0.385=0.52 \times\left(\frac{2.5}{ M } \times \frac{1000}{75}\right) $
$M =45\, g \,mol ^{-1}$