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The density of 2 M aqueous solution of NaOH is 1.28 g/cm³. The molality of the solution is [Given that molecular mass of NaOH = 40 g mol⁻¹]

1. 1.32m
2. 1.20m
3. 1.56m
4. 1.67m

Correct answer: 1.67m

Solution

To calculate molality, we first find the mass of the solution. For 1 L of solution (1000 mL), the mass is 1.28 g/cm³ × 1000 cm³ = 1280 g. The mass of NaOH in 1 L is 2 moles × 40 g/mol = 80 g. The mass of water is 1280 g - 80 g = 1200 g = 1.2 kg. Molality = moles of solute / mass of solvent in kg = 2 / 1.2 = 1.67m.

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