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

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

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0.25 molal aqueous solution means that

Moles of urea = 0.25 mole

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

Molar mass of urea = 14 + 2 + 12 + 16 + 14 + 2 = 6O g mol-1

0.25 mole of urea = 60 x 0.25 mole = 15 g

Total mass of the solution = 1000 + 15 g = 1015 g = 1.015 g

Thus, 1.015 kg of solution contain urea = 15 g

2.5 kg of solution will require urea = $\frac{15}{100}$ x 2.5 kg = 37g