A sample of urine containing 0.120 g of urea, NH2CONH2, was treated with an excess of nitrous acid. The acid reacted according to the following equation:
H2 + 2HNO2 → CO2 + 2N2 + 3H2O
The gas produced was passed through aqueous sodium hydroxide and the final volume measured.
What was this volume at room temperature and pressure?
A) 9.6 cm3
B) 14.4 cm3
C) 48.0 cm3
D) 96.0 cm3
Answer: D
- At room temperature and pressure, H2O will be a liquid.
- When the gases pass through aq NaOH (strong alkali), the acidic gases will be removed i.e. CO2 will be removed.
- The only gas remaining is N2.
Mr of urea = 60
No. of moles of urea = 0.120/60 = 2 x 10–3 mol
Based on reacting ratio,
No. of moles of N2 = 2 x 2 x 10–3 = 4 x 10–3 mol
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