The Soda-acid fire extinguisher contains

A soda-acid fire extinguisher operates on the principle of generating carbon dioxide gas through a chemical reaction to extinguish fires. It specifically contains a solution of sodium hydrogen carbonate (also known as baking soda) and a separate container of sulphuric acid [1]. When the extinguisher is activated, the acid and the sodium hydrogen carbonate solution mix, resulting in a reaction that produces sodium sulphate, water, and a large volume of carbon dioxide gas. The chemical equation for this process is H2SO4 + 2NaHCO3 -> Na2SO4 + 2CO2 + 2H2O. The carbon dioxide gas creates pressure to force the liquid out and acts to smother the fire by displacing oxygen. While other acids like tartaric acid were used historically, modern soda-acid extinguishers primarily utilize sulphuric acid for its strong reactivity with the alkaline sodium hydrogen carbonate [1].

Sources

1. [1] Science , class X (NCERT 2025 ed.) > Chapter 2: Acids, Bases and Salts > Uses of Baking soda > p. 31