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A KOH aqueous solution is 6.50 molal and has density 1.89 g/cm³. Calculate its molarity in mol/dm³ (round to the nearest integer). [Molar masses: K = 39.0, O = 16.0, H = 1.0]

1. 9
2. 11
3. 13
4. 7

Correct answer: 9

Solution

Molar mass of KOH = 56 g/mol. For 6.50 mol in 1 kg water, total mass = 1364 g, volume = 1364/1.89 = 721.7 mL, giving molarity = 6.50/0.7217 = 9.0 mol/dm³.

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