Carbon dioxide, CO₂, is a gas produced during respiration. Describe how the relative formula mass of carbon dioxide is determined, and state the relative formula mass of carbon dioxide. (Relative atomic masses: C = 12, O = 16.)
Written & reviewed by James Millett — Biology (Imperial College London), PGCE Science (University of Cambridge).
Model answer (4 marks)
The relative formula mass of CO₂ is found by adding the relative atomic masses of all the atoms in the formula.
1. There is one carbon atom contributing 12.
2. There are two oxygen atoms each contributing 16.
3. Calculation: 12 + 16 + 16 = 44.
The relative formula mass of carbon dioxide is 44.
1. There is one carbon atom contributing 12.
2. There are two oxygen atoms each contributing 16.
3. Calculation: 12 + 16 + 16 = 44.
The relative formula mass of carbon dioxide is 44.
Examiner tips
- Show the step‑by‑step addition of atomic masses; use the formula 12 + 2×16.
- Mention the number of each atom explicitly to demonstrate understanding.
- Include the final value 44 in the answer.
Mark scheme (4 marks)
- Relative formula mass is found by adding together the relative atomic masses of all the atoms in the formula
- Correct identification that there is one carbon atom contributing 12 and two oxygen atoms each contributing 16
- Correct calculation shown: 12 + 16 + 16 or 12 + (2 × 16)
- Relative formula mass of carbon dioxide = 44
Key terms in this question
relative formula mass · relative atomic mass · formula
Related
- All Cambridge International IGCSE Chemistry (0620) revision notes →
- How to answer a "Describe" question →
- Decode the mark scheme abbreviations →
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