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What is the molality of a urea solution prepared by dissolving 0.0100 g of urea, (NH2)2CO, in 0.3000 dm³ of water at STP?

1. 5.55 × 10⁻⁴ m
2. 33.3 m
3. 3.33 × 10⁻² m
4. 0.555 m

Correct answer: 5.55 × 10⁻⁴ m

Solution

Moles urea = 0.0100/60 = 1.667e-4 mol. Mass of water = 0.300 dm^3 ~ 0.300 kg. Molality = 1.667e-4 / 0.300 = 5.55e-4 m.

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