Which of the following compounds is used in soda-acid fire extinguishers?

Question

Examoogle · Accepted Answer

The correct answer is Option C: Sodium bicarbonate. A soda-acid fire extinguisher contains sodium bicarbonate ($NaHCO_3$) solution and a separate glass container filled with sulfuric acid ($H_2SO_4$). When the knob is struck, the acid mixes with the sodium bicarbonate to produce carbon dioxide gas ($CO_2$), which rapidly forces the liquid out and cuts off the oxygen supply to extinguish the fire.

Step-by-Step Solution & Concepts:
A soda-acid fire extinguisher contains sodium bicarbonate ($NaHCO_3$) solution and a separate glass container filled with sulfuric acid ($H_2SO_4$). When the knob is struck, the acid mixes with the sodium bicarbonate to produce carbon dioxide gas ($CO_2$), which rapidly forces the liquid out and cuts off the oxygen supply to extinguish the fire.

Working Principle: When the extinguisher is operated, sulfuric acid reacts with sodium bicarbonate to release carbon dioxide ($CO_2$) gas under high pressure. The chemical reaction is: $$2NaHCO_3 + H_2SO_4 \rightarrow Na_2SO_4 + 2H_2O + 2CO_2\uparrow$$. Carbon dioxide is heavier than air and non-supporter of combustion, forming a blanket over the fire and cutting off the supply of oxygen.

Key Formulas: $2NaHCO_3 + H_2SO_4 \rightarrow Na_2SO_4 + 2H_2O + 2CO_2\uparrow$ — Complete chemical reaction in soda-acid fire extinguisher

Key Points: Sodium bicarbonate ($NaHCO_3$) is a mild basic salt commonly known as baking soda.; Sulfuric acid ($H_2SO_4$) reacts vigorously with sodium bicarbonate to generate carbon dioxide gas.; Carbon dioxide ($CO_2$) is denser than air and acts as a blanketing agent to put out fires.; Soda-acid extinguishers are effective for Class A fires (wood, paper, cloth) but should not be used on electrical or oil fires.

Advantages: Quickly generates high pressure on activation; Effective for solid combustible fires (Class A); Inexpensive and easy to manufacture

Disadvantages: Can cause electrical shock if used on live electrical equipment; Not suitable for flammable liquid fires (Class B)

Applications: Extinguishing fires involving paper, wood, and textiles in offices and schools; Basic firefighting equipment in public buildings

Additional Info: Bleaching powder is $CaOCl_2$, used in water purification and textile industries.. Calcium chloride ($CaCl_2$) is used as a desiccant and de-icing agent.. Sodium carbonate ($Na_2CO_3$) is washing soda, used in glass manufacturing and water softening.

Answer: C is correct — Sodium bicarbonate is used along with sulfuric acid in soda-acid fire extinguishers to generate carbon dioxide gas which puts out the fire.

Exam Tip: Remember that sodium bicarbonate ($NaHCO_3$) releases $CO_2$ both in fire extinguishers and when heated in baking, making it a versatile compound in everyday chemistry.

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