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120 g of urea (molar mass 60 g/mol) is dissolved in 1000 g of water, giving a solution of density 1.15 g/mL. What is the molarity of the solution?

1. 2.05 M
2. 1.78 M
3. 2.00 M
4. 2.22 M

Correct answer: 2.05 M

Solution

Moles urea = 2. Solution mass = 1120 g, volume = 1120/1.15 = 973.9 mL = 0.9739 L. Molarity = 2/0.9739 = 2.05 M.

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