The density of 3 M solution of NaCl is $1.0 \mathrm{~g} \mathrm{~mL}^{-1}$. Molality of the solution is \_\_\_\_ $\times 10^{-2} \mathrm{~m}$. (Nearest integer). Given: Molar mass of Na and Cl is 23 and $35.5 \mathrm{~g} \mathrm{~mol}^{-1}$ respectively.

JEE Main · 2023 · 01 Feb 2023 · Shift 1 · Some Basic Concepts of Chemistry

The density of 3 M solution of NaCl is

1.0 g mL^{- 1}

. Molality of the solution is ____

\times 1 0^{- 2} m

. (Nearest integer).

Given: Molar mass of Na and Cl is 23 and

35.5 g mol^{- 1}

respectively.

Answer: 364

Taking one litre of the

3 M

solution, its mass is

1000 mL \times 1.0 g m L^{- 1} = 1000 g

. This litre holds

3 mol

of sodium chloride of molar mass

58.5 g mo l^{- 1}

, that is

175.5 g

, so the water present is

1000 - 175.5 = 824.5 g = 0.8245 kg

. The molality is

\frac{3}{0.8245} = 3.64 mol k g^{- 1}

, which in the required form is

364 \times 1 0^{- 2} m

. The value is 364.

JEE Main · 2023 · 01 Feb 2023 · Shift 1 · Integer answer