Calculate the mass of urea (NH2CONH2) re

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Target Exam

CUET

Subject

Chemistry

Chapter

Physical: Solutions

Question:

Calculate the mass of urea (NH₂CONH₂) required in making 2.5 kg of 0.25 molal aqueous solution.

Options:

32 g

37 g

42 g

50 g

Correct Answer:

37 g

Explanation:

0.25 molal aqueous solution of urea means that 0.25 mole of urea are present in 1 kg of water

Moles of urea =

0.25 m o l e

Mass of solvent (water) = 1 kg = 1000 g

Molar mass of urea (

N H_{2} C O N H_{2}

) = 60 g mol^-1

0.25 m o l e o f u r e a = 0.25 m o l \times 60 g m o l - 1 = 15 g

T o t a l m a s s o f s o l u t i o n = 1000 + 15 g = 1015 g = 1.015 k g

Thus; 1.015 kg of solution contain urea =

15 g

1 kg of the solution contains urea = \(\frac{15}{1.015}\)

2.5 k g

of solution will require urea = $\frac{15}{1.015}$ x 2.5 = 37 g