The percentage by mass of carbon in carbon dioxide, CO2, is about

  • A. 27.3 per cent
  • B. 12 per cent
  • C. 44 per cent
  • D. 72.7 per cent

Explanation

The molar mass is 12 + 32, that is 44, so the carbon fraction is 12 divided by 44 multiplied by 100, giving 27.3 per cent. The figure 72.7 per cent is the oxygen content, which is why it appears as a distractor, and the two must add to 100. Percentage composition is the first step in working out an empirical formula from experimental data.

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