Question

0.70 g of an organic compound, when dissolved in 32 g of acetone, produces an elevation of 0.25°C in the boiling point. Calculate the molecular mass of the organic compound (K_b for acetone = 1.72 K kg mol⁻¹).

Answer 1

Given: Mass of solute (organic compound), w₂ = 0.70 g

Mass of solvent (acetone), w₁ = 32 g

Elevation in boiling point, ΔT_b = 0.25°C

K_b (for acetone) = 1.72 K kg mol⁻¹

We need to find the molecular mass (M) of the compound.

`Delta T_b = K_b * (w_2 xx 1000)/(M xx w_1)`

`M = (K_b xx w_2 xx 1000)/(Delta T_b xx w_1)`

= `(1.72 xx 0.70 xx 1000)/(0.25 xx 32)`

= `1204/8`

= 150.5 g/mol

∴ The molecular mass of the organic compound is 150.5 g/mol.