What is the chemical composition of a soda-acid type fire extinguisher?
Solution of sodium hydrogen carbonate and sulfuric acid
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.
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.
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.
Let's look at the given options based on our understanding of the soda-acid fire extinguisher's composition:
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.
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.
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.
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.
| 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 |
Different types of fire extinguishers are used for different classes of fires. Understanding the composition helps determine which type is suitable:
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.
Which one of the following is used in soda-acid fire extinguishers?
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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.
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