All Exams Test series for 1 year @ ₹349 only
Question

What is the chemical composition of a soda-acid type fire extinguisher?

This question was previously asked in
CDS I 2023 English Previous Year Paper (16-April-2023)
The correct answer is

Solution of sodium hydrogen carbonate and sulfuric acid  

Understanding Soda-Acid Fire Extinguisher Composition

A soda-acid type fire extinguisher is designed to put out fires, particularly those involving combustible solids like wood, paper, and textiles (Class A fires). It works by producing carbon dioxide (\(\text{CO}_2\)) gas, which is heavier than air and blankets the fire, cutting off its oxygen supply. The key to this process is the chemical reaction between two main components stored separately within the extinguisher.

How a Soda-Acid Fire Extinguisher Works

Inside a soda-acid fire extinguisher, there is typically a solution of sodium hydrogen carbonate (also known as sodium bicarbonate, baking soda) and a small bottle containing sulfuric acid. When the extinguisher is activated (usually by inverting it or striking a knob), the bottle of sulfuric acid breaks, allowing the acid to mix with the sodium hydrogen carbonate solution.

This mixing causes a chemical reaction that rapidly produces a large volume of carbon dioxide gas. The pressure from this gas expels the mixture (mainly water and \(\text{CO}_2\)) from the nozzle onto the fire.

Chemical Reaction

The chemical reaction that occurs is between sodium hydrogen carbonate (\(\text{NaHCO}_3\)) and sulfuric acid (\(\text{H}_2\text{SO}_4\)). The balanced chemical equation for this reaction is:

\(2\text{NaHCO}_3\text{(aq)} + \text{H}_2\text{SO}_4\text{(aq)} \rightarrow \text{Na}_2\text{SO}_4\text{(aq)} + 2\text{H}_2\text{O}\text{(l)} + 2\text{CO}_2\text{(g)}\)

As you can see, carbon dioxide (\(\text{CO}_2\)) gas is a product of this reaction, along with sodium sulfate (\(\text{Na}_2\text{SO}_4\)) and water (\(\text{H}_2\text{O}\)). The released \(\text{CO}_2\) is the primary extinguishing agent, displacing oxygen around the fire.

Analyzing the Options

Let's look at the given options based on our understanding of the soda-acid fire extinguisher's composition:

  • Option 1: Solution of sodium hydrogen carbonate and sulfuric acid

    This matches the description of the chemical components used in a soda-acid fire extinguisher. Sodium hydrogen carbonate solution reacts with sulfuric acid to produce carbon dioxide gas.

  • Option 2: Solution of sodium carbonate and sulfuric acid

    Sodium carbonate (\(\text{Na}_2\text{CO}_3\)) also reacts with sulfuric acid (\(\text{H}_2\text{SO}_4\)) to produce carbon dioxide, but sodium hydrogen carbonate (\(\text{NaHCO}_3\)) is the standard chemical used in this type of extinguisher due to practical considerations regarding reaction speed and storage.

  • Option 3: Solution of carbon dioxide and sulfuric acid

    Carbon dioxide (\(\text{CO}_2\)) is the gas produced by the reaction, not one of the initial reactants stored in the extinguisher. It's the product that helps extinguish the fire.

  • Option 4: Solution of sodium chloride and sulfuric acid

    Sodium chloride (\(\text{NaCl}\)) reacts with sulfuric acid (\(\text{H}_2\text{SO}_4\)) to produce hydrogen chloride gas (\(\text{HCl}\)) and sodium sulfate (\(\text{Na}_2\text{SO}_4\)). This reaction does not produce carbon dioxide, so it would not work as a soda-acid fire extinguisher.

Based on the chemical reaction that produces carbon dioxide for extinguishing fires, the correct composition involves sodium hydrogen carbonate and sulfuric acid.

Revision Table: Key Components

Component Chemical Name Chemical Formula Role in Extinguisher
Component 1 Sodium Hydrogen Carbonate \(\text{NaHCO}_3\) Reactant (base/carbonate source)
Component 2 Sulfuric Acid \(\text{H}_2\text{SO}_4\) Reactant (acid)
Product Gas Carbon Dioxide \(\text{CO}_2\) Extinguishing Agent

Additional Information on Fire Extinguisher Types

Different types of fire extinguishers are used for different classes of fires. Understanding the composition helps determine which type is suitable:

  • Water Extinguishers: Used for Class A fires (solids). They cool the burning material.
  • Foam Extinguishers: Used for Class A and B fires (flammable liquids). They cool and smother the fire.
  • Dry Powder Extinguishers: Used for Class A, B, and C fires (flammable gases, electrical). They interrupt the chemical reaction and smother the fire. Some types are also effective on metal fires (Class D).
  • CO\(_2\) Extinguishers: Used for Class B and electrical fires (Class C). They displace oxygen and cool the fire, but the CO\(_2\) from soda-acid types also carries water/solution which isn't suitable for electrical fires.
  • Wet Chemical Extinguishers: Used for Class F fires (cooking oils/fats). They cool and create a soapy layer to prevent re-ignition.

The soda-acid extinguisher, primarily containing water and producing \(\text{CO}_2\), is effective on Class A fires but dangerous for electrical fires (Class C) due to the water content and not suitable for liquid (Class B) or metal (Class D) fires.

Was this answer helpful?

Similar Questions

  1. Which one of the following is used in soda-acid fire extinguishers?

  2. Which one of the following gases is released mostly from landfills in urban areas?

  3. Which one among the following pairs of compound and chemical formula is not correctly matched ?
  4. Consider the following statements :
    1. The temporary hardness in water is due to the presence of bicarbonates of calcium.
    2. The permanent hardness in water is due to the presence of soluble chlorides and sulphates of calcium and magnesium.
    3. The permanent hardness in water is removed by adding \(Na_2CO_3\) to water.
    Which of the statements given above are correct ?

  5. Which one among the following statements regarding micelles is not correct ?
  6. After a hot sunny day, people sprinkle water on the roof-top because:

  7. Methyl Isocyanate gas, which was involved in the disaster in Bhopal in December 1984, was used in the Union Carbide factory for the production of:

  8. ‘German silver’ is used to make decorative articles, coinage metal, ornaments, etc. The name is given because:

  9. Why do plastics not degrade easily ?
  10. Which one of the following sodium compounds is used for softening hard water?


Important Questions from Chemistry in Everyday Life

  1. Which of the following is a greenhouse gas?

    I. Methane

    II. Nitrous oxide

  2. The gas which turns lime water milky is:

  3. Liquefied Petroleum Gas (LPG) is mainly a mixture of:

  4. Among the following, the conducting form of carbon is

  5. Which of the following is NOT a Fossil Fuel?

Need Expert Advice?
Test Series
CDS img
Defence
UPSC CDS 2026 Mock Test Series
536 Tests 4 Tests Free
1633 Attempts
4.3(174)
English, Hindi
More Questions from CDS

Start Your Preparation with Prepp Mobile App

Download the app from Google Play & App Store
Download the app from Google Play & App Store
Prepp Mobile App