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The density of a solution prepared by dissolving 120 g of urea (mol. mass = 60 u) in 1000 g of water is 1.15 g/mL. The molarity of this solution is:

1. 0.50 M
2. 1.78 M
3. 1.02 M
4. 2.05 M

Correct answer: 2.05 M

Solution

Moles urea = 120/60 = 2 mol. Total solution mass = 120 + 1000 = 1120 g; volume = 1120/1.15 = 973.9 mL = 0.974 L. Molarity = 2/0.974 = 2.05 M.

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