Question

A solution prepared by dissolving 0.25 grams of a non-volatile solute in 50 mL of benzene

decreases the freezing point by 0.4K. Calculate the molar mass of the solute.(Given: Kb for

benzene = 5.12K/m ; density of benzene = 0.8g/mL)​

Answer 1

Answer:

The molar mass of the solute is 80 g/mol.

Explanation:

Given:

Kf (although it reads Kb it's actually Kf) = 5.12 K kg/mol, ΔTf=0.4K, W₂=0.25g

V₁=50mL, ρ of solvent=0.8 g/mL

Sol:

W₁ = V₁  x  ρ of solvent = 50mL x 0.8 g/mL = 40g

M₂ = (Kf × W₂ × 1000) / (ΔTf × W₁) = (5.12 x 0.25 x 1000) / (0.4 x 40) = 80 g/mol