Which one of the following is used in soda-acid fire extinguishers ?
- A.Sodium chloride
- B.Sodium hydrogen carbonate
- C.Calcium hydroxide
- D.Acetic acid
Correct answer
Explanation
The correct answer is B, Sodium hydrogen carbonate. A soda-acid extinguisher holds a solution of sodium hydrogen carbonate (baking soda) and a small bottle of sulphuric acid; when the two mix, carbon dioxide is released.
Striking the knob breaks the acid bottle, and the reaction 2NaHCO₃ + H₂SO₄ → Na₂SO₄ + 2H₂O + 2CO₂ produces a burst of carbon dioxide. The gas pressure forces a stream of water and solution out of the nozzle onto the fire, cooling the burning material, while the carbon dioxide helps cut off oxygen. Such extinguishers suit fires of wood, paper and cloth, but not electrical or oil fires, since water conducts electricity and spreads burning oil.
A, sodium chloride, is common salt and gives no gas with acid in this way. C, calcium hydroxide, is slaked lime, used in whitewash and to reduce soil acidity. D, acetic acid, is the acid in vinegar and is not the base used in the extinguisher.
Exam tip: soda-acid extinguisher = NaHCO₃ + H₂SO₄ → CO₂; not for electrical or oil fires.
Practice Questions
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- A.perpendicular to each other.
- B.parallel to each other.
- C.anti-parallel to each other.
- D.equal in magnitude.
Show answer
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- A.Satellite is kept in orbit by remote control from ground station.
- B.Satellite is kept in orbit by retro-rocket and solar energy keeps it moving around the Earth.
- C.Satellite requires energy from solar panels and solid fuels for orbiting.
- D.Satellite does not require any energy for orbiting.
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- A.Frictional force
- B.Electric force
- C.Gravitational force
- D.Spring force
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- A.electrical signals to sound waves
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- C.microwaves to sound waves
- D.sound waves to microwaves
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- B.bending away from the normal
- C.propagating in straight line
- D.reflected towards the opposite direction
Show answer
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