Sodium hydrogencarbonate (NaHCO₃) is used as an antacid and also as an ingredient in baking powder. Write the equation for its decomposition on heating and explain why it makes bread soft and spongy.
Generated by claude-sonnet-4-6 · 2026-06-26 01:04 · grounding rag
Model Answer
Decomposition reaction on heating:
$$2\text{NaHCO}_3 \xrightarrow{\Delta} \text{Na}_2\text{CO}_3 + \text{H}_2\text{O} + \text{CO}_2\uparrow$$
Why bread becomes soft and spongy:
When baking powder is heated or mixed with water, NaHCO₃ reacts with the edible acid (e.g., tartaric acid) present and releases CO₂ gas. This CO₂ gets trapped in the dough, causing it to rise and making the bread soft and spongy.
Source: Chapter 2, Section 2.4.3 — Baking soda
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Explanation
- The equation must be balanced and include the heat arrow (Δ); missing it loses marks.
- The key point examiners look for: CO₂ is the gas responsible for making bread spongy — state this explicitly.
- Note the two scenarios given in the textbook: NaHCO₃ decomposes on heating alone, but in baking powder it also reacts with an acid to release CO₂. Since the question asks about baking powder use, mentioning the acid reaction is ideal.
- Do not confuse the decomposition equation (2 mol NaHCO₃) with the single-mol acid reaction equation.