Question

1. A solution prepared by adding 10g of an unknown non-volatile, non-electrolyte solute to 150 g of water. The Boiling point of the solution is elevated by 0.433 ⁰C above the normal boiling point of the solvent. What is the molar mass of the unknown substance?

Answer 1

$\Delta T_b=k_b.M.i$

Taking $k_b$ of water as 0.515°C$/m$

$0.433=0.515×M×1$

$M=0.8408M$

Mass of solid in 1 kg of water

$=\frac{1000}{150}×10=66.67g$

$66.67g\equiv0 .8408M$

Molar mass $=\frac{1}{0.8408}×66.67$

$=79.29g$