Science (086) — CBSE Class 10 board question

(i) As an antacid:
Baking soda (NaHCO₃) is a mild base (alkaline in nature). It neutralises excess hydrochloric acid present in the stomach, relieving indigestion.
$$\text{NaHCO}_3 + \text{HCl} \rightarrow \text{NaCl} + \text{H}_2\text{O} + \text{CO}_2$$

(ii) As a constituent of baking powder:
On heating, NaHCO₃ decomposes to release CO₂ gas, which makes the dough soft and fluffy (acts as a leavening agent).
$$2\text{NaHCO}_3 \xrightarrow{\Delta} \text{Na}_2\text{CO}_3 + \text{H}_2\text{O} + \text{CO}_2\uparrow$$

(iii) In soda-acid fire extinguishers:
When NaHCO₃ reacts with sulphuric acid, CO₂ is produced in large quantities. CO₂ being heavier than air cuts off the oxygen supply and extinguishes the fire.
$$2\text{NaHCO}_3 + \text{H}_2\text{SO}_4 \rightarrow \text{Na}_2\text{SO}_4 + 2\text{H}_2\text{O} + 2\text{CO}_2\uparrow$$

Source: Chapter 2, Acids, Bases and Salts

---

• Each part carries 1 mark. Examiner looks for: the chemical property (basic/alkaline nature → neutralisation; decomposition on heating; reaction with acid to give CO₂) AND the reason it is useful.
• Including balanced equations earns full marks and demonstrates the property clearly — always write them if you remember them.
• Key terms to use: neutralisation, decomposition, CO₂ released, alkaline nature.