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

Explanation

`"Molality of solution"=("Mass of urea/Molar mass of urea")/("Mass of water in kg")`
`"Molality of solution"=0.25 m=(0.25 mol kg^(-1))`
Molar mass of urea `(NH_(2)CONH_(2))=2xx14+1xx12+1xx16+4xx1= 60 g mol^(-1)`.
Mass of solvent (water)=2.5 kg
`(0.25 mol kg^(-1)),=("Mass of urea")/((60g mol^(-1))xx(2.5 kg))`
`"Mass of urea"= (0.25 mol kg^(-1))xx(60 g mol^(-1))xx(2.5 kg)=37.5` g