When charcoal reacts in the presence of oxygen, carbon monoxide and carbon dioxide are produced according to the following chemical reactions.
2C(s) + O2(g) → 2CO(g)
C(s) + O2(g) → CO2(g)
What would be the total mass of gas produced when 400 g of charcoal is reacted, assuming equal amounts are consumed in each reaction?
A) 0.93 kg
B) 1.2 kg
C) 1.5 kg
D) 2.5 kg
Answer: B
- Equal amounts are consumed i.e. 200 g of C undergoes each reaction
No. of moles of C reacted in each reaction = 200/12 = 16.67 mol
No. of moles of CO formed = 16.67 mol
Mass of CO formed = 16.67 x (12+16) = 466.67 g
No. of moles of CO2 formed = 16.67 mol
Mass of CO2 formed = 16.67 x (12+16x2) = 733.33 g
Total mass of gas formed = 1200 g = 1.2 kg
Question 2
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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