Question

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

$\Delta\>T_b=k_b.m.$

$k_b$ For water $=0.515°C/M$

$0.433=0.515M$

$M=0.8407M$

Mass of solution in 1kg of water $=\frac{1000}{150}×10=66.67g$

Molar mass of solute $=\frac{1}{0.8408}×66.67=79.30g$