A student reacts calcium carbonate with excess hydrochloric acid. The equation for the reaction is: CaCO₃ + 2HCl → CaCl₂ + H₂O + CO₂. The student uses 5.0 g of calcium carbonate. The relative formula mass (Mr) of calcium carbonate is 100. The Mr of carbon dioxide is 44. Explain how the student can calculate the theoretical yield of carbon dioxide produced, and state the theoretical yield in grams.
Written & reviewed by James Millett — Biology (Imperial College London), PGCE Science (University of Cambridge).
Calcium carbonate reacts with hydrochloric acid in a 1:1 molar ratio with carbon dioxide as one of the products. The theoretical yield is the maximum possible mass of product that can be obtained from a reaction.
Model answer (5 marks)
1. 5.0 g CaCO₃ ÷ 100 g mol⁻¹ = 0.050 mol CaCO₃
2. From the balanced equation 1 mol CaCO₃ gives 1 mol CO₂, so 0.050 mol CO₂
3. 0.050 mol CO₂ × 44 g mol⁻¹ = 2.2 g CO₂
4. The theoretical yield of CO₂ is 2.2 g
5. Theoretical yield is the maximum mass that can be obtained if the reaction goes to completion; the actual yield is usually lower due to losses and incomplete reaction.
2. From the balanced equation 1 mol CaCO₃ gives 1 mol CO₂, so 0.050 mol CO₂
3. 0.050 mol CO₂ × 44 g mol⁻¹ = 2.2 g CO₂
4. The theoretical yield of CO₂ is 2.2 g
5. Theoretical yield is the maximum mass that can be obtained if the reaction goes to completion; the actual yield is usually lower due to losses and incomplete reaction.
Examiner tips
- Show the calculation steps and units; use the 1:1 molar ratio directly; state the final mass in grams; explain the definition of theoretical yield
Common mistakes
- Using the wrong molar mass for CaCO₃ or CO₂; forgetting to multiply by the molar mass; mis‑applying the 1:1 ratio; not stating that the yield is a maximum
Mark scheme (5 marks)
- Calculate the number of moles of calcium carbonate used
- Use the molar ratio from the balanced equation to determine moles of carbon dioxide
- Use mass = moles × Mr to calculate the mass of carbon dioxide
- States the correct theoretical yield of carbon dioxide
- Explains that the theoretical yield is the maximum possible mass of product and that the actual yield is normally less
Key terms in this question
theoretical yield · relative formula mass
Related
- All Edexcel A-Level Chemistry (9CH0) revision notes →
- How to answer a "Explain" question →
- Decode the mark scheme abbreviations →
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