[short_answer] In a soda-acid fire extinguisher, dilute sulphuric acid reacts with sodium hydrogencarbonate solution. (a) Write the balanced chemical equation for this reaction. (b) Name the gas produced and explain two properties of this gas that make it effective at extinguishing a fire.
Generated by claude-sonnet-4-6 · 2026-06-26 01:05 · grounding rag
Model Answer
(a) The balanced chemical equation is:
$$\text{H}_2\text{SO}_4 \text{(dil.)} + 2\text{NaHCO}_3 \rightarrow \text{Na}_2\text{SO}_4 + 2\text{H}_2\text{O} + 2\text{CO}_2\uparrow$$
(b) The gas produced is carbon dioxide (CO₂).
Two properties that make it effective:
- CO₂ does not support combustion — it neither burns nor allows other substances to burn, so it cuts off the fuel's oxygen supply.
- CO₂ is heavier than air — it forms a blanket over the burning material, cutting off the supply of oxygen and smothering the fire.
Source: Chapter 2, Acids Bases and Salts; Chapter 1, Chemical Reactions and Equations
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Explanation
- The equation is the most commonly asked part — ensure it is balanced (coefficient 2 before NaHCO₃, H₂O, and CO₂).
- For part (b), examiners expect two distinct properties — non-supporter of combustion AND heavier than air (blanket effect). Mentioning only one will cost a mark.
- Avoid vague answers like "it puts out fire" — name the specific property (non-supportive of combustion, density higher than air).