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A 3 M aqueous sodium chloride solution has density 1.252 g/mL. Find its molality. (Molar mass NaCl = 58.5 g/mol)

1. 2.79 m
2. 2.18 m
3. 3.00 m
4. 2.60 m

Correct answer: 2.79 m

Solution

1 L weighs 1252 g; 3 mol NaCl = 175.5 g, so water = 1076.5 g = 1.0765 kg; molality = 3/1.0765 = 2.79 m.

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