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

Answer

`36.945g`

Explanation

`W_(sol)=2.5kg=2.5xx1000g=2500g`
`Mw_(2)(NH_(2)CONH_(2))=14+2+12+16+14+2`
`=60g mol^(-1)`
`W_(1)(` solvent, `H_(2)O)=(W_(sol)-W_(2))=(2500-W_(2))g`
`W_(2)=?`
Using the formula
`m=(W_(2)xx1000)/(Mw_(2)xxW_(1))`
`0.25=(W_(2)xx1000)/(60xx(2500-W_(2)))`
Solve for `W_(2)`
`W_(2)=36.945g`