Calculate the mass of urea `(NH_(2)CONH_(2))` required in making `2.5 kg `of `0.25 `molal aqueous solution.

Options

A. 37 g
B. 25 g
C. 125 g
D. 27.5 g

Answer

A

Explanation

No. of moles of urea =0.25 moles
Mass of solvent = 1 kg = 1000 g
Molar mass of urea =`60 g mol^(-1)`
Mass of urea in 1000 g of `H_2O = 0.25xx60`=15 g
Total mass of solution=1000+15=1015 g
1.015 kg solution contains 15 g urea 2.5 kg solution will contain =`15/1.015xx2.5`= 37 g