Density of a 2.05 M solution of acetic acid in water is $1.02 \mathrm{~g} / \mathrm{mL}$. The molality of the solution is

(C) $2.28 \mathrm{~mol} \mathrm{~kg}^{-1}$

(A) $1.14 \mathrm{~mol} \mathrm{~kg}^{-1}$

(B) $3.28 \mathrm{~mol} \mathrm{~kg}^{-1}$

(D) $0.44 \mathrm{~mol} \mathrm{~kg}^{-1}$

JEE Main · 2006 · 30 Apr 2006 · Offline · Some Basic Concepts of Chemistry

Density of a 2.05 M solution of acetic acid in water is

1.02 g / mL

. The molality of the solution is

Answer: (C)

Take one litre of the

2.05 M

solution, whose mass is

1000 \times 1.02 = 1020 g

. It contains

2.05

moles of acetic acid, which at

60 g mo l^{- 1}

weigh

123 g

, so the water present is

1020 - 123 = 897 g

, or

0.897 kg

. Molality is moles of solute per kilogram of solvent,

\frac{2.05}{0.897} \approx 2.28 mol k g^{- 1}

JEE Main · 2006 · 30 Apr 2006 · Offline · Single correct option