The Soda-acid fire extinguisher contains
- A.sulphuric acid and solution of sodium hydrogencarbonate
- B.nitric acid and solution of sodium hydrogencarbonate
- C.sulphuric acid and solution of sodium carbonate
- D.sulphuric acid and solution of potassium carbonate
Correct answer
Explanation
The correct answer is A, sulphuric acid and solution of sodium hydrogencarbonate. When the two mix, they release a rush of carbon dioxide that pushes water out onto the fire.
In a soda-acid extinguisher a small bottle of dilute sulphuric acid sits inside a cylinder filled with a solution of sodium hydrogencarbonate (baking soda, NaHCO3). Striking the knob breaks the bottle, and the reaction 2NaHCO3 + H2SO4 → Na2SO4 + 2H2O + 2CO2 produces carbon dioxide gas. The pressure of the gas forces a jet of water out of the nozzle. The water cools the burning material and the carbon dioxide helps cut off oxygen. Because it throws water, it is meant for wood, paper and cloth fires, not for electrical or oil fires.
Option B is wrong because nitric acid is not used; sulphuric acid is the acid in this device. Option C is wrong because the alkali is sodium hydrogencarbonate, not sodium carbonate (washing soda). Option D is wrong because potassium carbonate is not used either.
Exam tip: soda-acid = NaHCO3 + H2SO4 → CO2; not for electrical or oil fires.
Practice Questions
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