Calculate the mass of urea \((NH_2CONH_2)\) required in making \(2.5 kg\) of \(0.25\) molal aqueous solution.
Answer & explanation
Correct answer: option 1
The correct answer is Option (1) → 36.95 g
A 0.25 molal solution has 0.25 mol of urea in 1 kg of water. Molar mass of urea, \( \ce{NH2CONH2} \) = 60 g mol−1.
\( \displaystyle \text{Mass of urea per kg of water} = 0.25 \times 60 = 15\ \text{g} \)
\( \displaystyle \text{Mass of this solution} = 1000 + 15 = 1015\ \text{g} \)
\( \displaystyle \text{Mass of urea in 2500 g of solution} = \frac{15 \times 2500}{1015} = 36.95\ \text{g} \)
Note: This question is from NCERT (2026-27). NTA sets numerical questions from NCERT too, so do not ignore NCERT while practising numericals.
NCERT (2026-27 edition):
Intext Questions – “1.4 Calculate the mass of urea (NH2CONH2) required in making 2.5 kg of 0.25 molal aqueous solution.”