Single Choice

The molality of the solution containing 15.20 g of urea (molar mass = 60) dissolved in 150 g of water is:

A$$1.689\, mol \, kg^{-1}$$
Correct Answer
B$$0.1689 \, mol \, kg^{-1}$$
C$$0.5922\, mol \, kg^{-1}$$
D$$0.2533 \, mol \, kg^{-1}$$

Solution

$$\displaystyle \text { molality } = \dfrac { \text { mass of urea } }{ \text { molar mass of urea } \times \text { mass of water in kg} }$$

$$\displaystyle \text { molality } = \dfrac { \text { 15.20 g} }{ \text { 60 g/mol} \times \text { 0.150 kg} } $$

$$\displaystyle \text { molality } = \text { 1.689 mol/kg} $$

Hence, option A is correct.

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