2.4 Calculate the mass of urea (NH CONH2) required in making 2.5 kg of

1.	2.4 Calculate the mass of urea (NH CONH2) required in making 2.5 kg of0.25 molal aqueous solution.
Answer» Molar mass of urea (NH2CONH2) = 2 (1 × 14 + 2 × 1) + 1 × 12 + 1 × 16= 60 g mol - 1 0.25 molar aqueous solution of urea means:1000 g of water contains 0.25 mol = (0.25 × 60)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 = (15 X 2500) / (1000+15) g = 36.95 g = 37 g of urea (approximately) Hence, mass of urea required = 37 g

2.4 Calculate the mass of urea (NH CONH2) required in making 2.5 kg of0.25 molal aqueous solution.

Answer»

Molar mass of urea (NH2CONH2) = 2 (1 × 14 + 2 × 1) + 1 × 12 + 1 × 16= 60 g mol - 1

0.25 molar aqueous solution of urea means:1000 g of water contains 0.25 mol = (0.25 × 60)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 = (15 X 2500) / (1000+15) g

= 36.95 g

= 37 g of urea (approximately)

Hence, mass of urea required = 37 g