# Sodium hydrogencarbonate, NaHCO₃, decomposes on heating according to the equation: 2NaHCO₃(s) → Na₂CO₃(s) + H₂O(g) + CO₂(g). A student heats a sample of NaHCO₃ until decomposition is complete. Explain how the student could use the masses recorded before and after heating to determine the percentage yield of Na₂CO₃, and state one assumption that must be made for this calculation to be valid.

> IB DP Chemistry Standard Level (2023 syllabus) — R2.1 How much? The amount of chemical change · Explain · 4 marks

## Mark scheme (4 marks)

1. The theoretical yield of Na₂CO₃ is calculated from the initial mass of NaHCO₃ using stoichiometric mole ratios (2 mol NaHCO₃ produces 1 mol Na₂CO₃).
2. The actual yield of Na₂CO₃ is obtained from the mass of solid remaining after heating (the residue mass).
3. Percentage yield is calculated as (actual yield / theoretical yield) × 100.
4. A valid assumption is that the residue consists entirely / only of Na₂CO₃ (i.e., no NaHCO₃ remains unreacted and no other solid product is formed).

## Key terms

- [percentage yield](https://www.gradenine.co.uk/glossary/percentage-yield)

## Related

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Source: [GradeNine](https://www.gradenine.co.uk/q/sodium-hydrogencarbonate-nahco-decomposes-on-heating-dc63a434) · Published by Druglandscape Ltd.