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In an aqueous solution the mole fraction of the solvent (water) is 0.8. Find the molality of the solution (in mol/kg).

1. 13.88 * 10⁻¹
2. 13.88 * 10⁻²
3. 13.88
4. 13.88 * 10⁻³

Correct answer: 13.88

Solution

With x_solute = 0.2 and x_water = 0.8 per mole of mixture, water mass = 0.8*18 g, giving molality = 0.2/(0.0144) = 13.88 mol/kg.

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