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

Explanation

Molar mass of urea `(NH_(2)CONH_(2))`
`= 2(1xx14+2xx1)+1xx12+1xx16`
`= 60 g mol^(-1)`
0.25 molar aqueous solution of urea means :
1000 g of water contains 0.25 mol
`= (0.25xx60)` g of urea
= 15 g of urea
That is,
`(1000+15)` g of solution contains 15 g of urea Therefore, 2.5 kg (2500 g) of solution contains
`=(15xx2500)/(1000xx15)g`
= 36.95 g
= 37 g of urea (approximately)
Hence, mass of urea required = 37 g