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

Answer

37.5 g

Explanation

Molar mass of urea, `NH_(2)CONH_(2)=14xx2+1xx4+12+16`
`=60"g mol"^(-1)=6xx10^(-2)"kg mol"^(-1)`
Molality `=("Moles of urea")/("kg of water")=("Mass of urea/Molar mass")/("kg of water")`
`=0.25=(w//6.0xx10^(-2))/(2.5`
`w=0.25 xx 2.5 xx 6.0 xx 10^(-2) kg =3.75 xx 10^(-2) kg =37.5 g`