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A solution of ethanol (C2H5OH) and water contains 54% water by mass. Given that the density of the solution is 1 g/mL, which of the following options are correct?

1. Molality_(C2H5OH) = 18.52
2. % w/w_(C2H5OH) = 46
3. X_(C2H5OH) = 0.25
4. % w/v_(C2H5OH) = 46

Correct answer: % w/w_(C2H5OH) = 46

Solution

In 100 g solution: 46 g ethanol (1 mol) and 54 g water (3 mol). All four options are numerically correct: molality = 1/0.054 = 18.52 m, %w/w = 46, mole fraction = 1/4 = 0.25, and since density = 1 g/mL so 100 g = 100 mL, %w/v = 46 g/100 mL * 100 = 46%.

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