Correct Answer: 73
Increase in mass of CaCl2 tube corresponds to mass of water formed.
Mass of H2O = 0.15 g
Moles of H2O:
0.15 / 18 = 0.00833 mol
Moles of hydrogen atoms:
= 2 × 0.00833 = 0.01666 mol
Mass of hydrogen:
= 0.01666 × 1 = 0.01666 g
Increase in mass of potash tube corresponds to mass of CO2.
Mass of CO2 = 0.1837 g
Moles of CO2:
0.1837 / 44 = 0.004175 mol
Moles of carbon atoms:
= 0.004175 mol
Mass of carbon:
= 0.004175 × 12 = 0.0501 g
Total mass of compound = 0.25 g
Mass of oxygen in compound:
= 0.25 − (0.0501 + 0.01666)
= 0.18324 g
Percentage of oxygen:
(0.18324 / 0.25) × 100 ≈ 73.3%
Nearest integer value:
= 73%
Hence, the percentage of oxygen in compound A is 73%.
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