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31/12/2021 4:37 pm
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Calculate the mass of urea (NH2CONH2) required in making 2.5 kg of 0.25 molal aqueous solution.
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31/12/2021 4:40 pm
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 = \(\frac{15 \times 2500}{1000 + 15}\)g
= 36.95 g
= 37 g of urea (approximately)
Hence, mass of urea required = 37 g