$2.5 g$ of a non-volatile non-electrolyte dissolved in $50 g$ of benzene raises its boiling point by $0.85 K$ . Given $K_{b} (benzene) = 2.53 K kg mo l^{- 1}$ , find the molar mass of the solute in $g mo l^{- 1}$ , to the nearest integer.

Numerical answer type, answer in g/mol, tolerance 1.

Answer: 149 g/mol

Δ T_{b} = K_{b} \frac{w \times 1000}{M W}

, so

M = \frac{1000 K _{b} w}{Δ T _{b} W} = \frac{1000 \times 2.53 \times 2.5}{0.85 \times 50} = 148.82 \approx 149 g mo l^{- 1}