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When 8 g of NaOH is dissolved in 18 g of water, find respectively the mole fraction of NaOH in the solution and the molality of the solution (in mol/kg). (Molar masses: NaOH = 40, H2O = 18)

1. 0.167, 11.11
2. 0.2, 22.20
3. 0.2, 11.11
4. 0.167, 22.20

Correct answer: 0.167, 11.11

Solution

Mole fraction = 0.2/1.2 = 0.167; molality = 0.2 mol / 0.018 kg = 11.11 mol/kg.

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