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A 2 M aqueous solution of NH4Cl (density = 3.107 g/mL) is fully dissociated as NH4Cl -> NH4+ + Cl-. Calculate the molality of each ion in the solution. (Molar mass of NH4Cl = 53.5)

1. 0.667 m each
2. 2.0 m each
3. 1.0 m each
4. 0.333 m each

Correct answer: 0.667 m each

Solution

Per litre the solution has 3 kg water and 2 mol salt, giving molality 0.667 m for the salt, hence 0.667 m for each ion.

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