What is the chemical composition of a soda-acid type fire extinguisher?
- A.Solution of sodium hydrogen carbonate and sulfuric acid
- B.Solution of sodium carbonate and sulfuric acid
- C.Solution of carbon dioxide and sulfuric acid
- D.Solution of sodium chloride and sulfuric acid
Correct answer
Explanation
The correct answer is A, Solution of sodium hydrogen carbonate and sulfuric acid. A soda-acid extinguisher uses sodium hydrogen carbonate (baking soda) solution and sulphuric acid, which react to release carbon dioxide.
In this extinguisher the sulphuric acid is kept in a separate container inside a cylinder filled with sodium hydrogen carbonate solution. When the extinguisher is operated, the two mix: 2NaHCO3 + H2SO4 gives Na2SO4 + 2H2O + 2CO2. The carbon dioxide gas builds up pressure and drives a jet of water and gas out of the nozzle. The water cools the burning material and the carbon dioxide helps cut off the oxygen supply. It suits fires of wood, paper and cloth, but not electrical or oil fires.
B is wrong because the extinguisher uses sodium hydrogen carbonate, not sodium carbonate (washing soda). C is wrong because carbon dioxide is the product of the reaction, not a starting solution. D is wrong because sodium chloride does not react with sulphuric acid to produce a jet of carbon dioxide.
Exam tip: Soda-acid extinguisher = NaHCO3 + H2SO4, releases CO2; not for electrical or oil fires.
Practice Questions
View allWhich one of the following is not true for anodizing process?
- A.It makes aluminium corrosion resistant.
- B.Metals like aluminium, titanium and magnesium can be anodized.
- C.Clean aluminium article is the anode and oxygen gas is evolved at the cathode.
- D.It is used in aircraft industry.
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In anodizing the clean aluminium article is indeed the anode, but oxygen is released at the anode, not at the cathode; hydrogen is released at the cathode.
Read the full explanation →Which one of the following statements is not correct?
- A.The response of the ear to sound of increasing intensity is approximately logarithmic.
- B.The sensitivity of the human ear does not vary with the frequency of the sound.
- C.When two or more waves traverse the same medium, the displacement of any element of the medium is the algebraic sum of the displacements due to each wave.
- D.Longitudinal waves can travel in all media—solids, liquids and gases.
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Read the full explanation →Kwashiorkor disease in children is caused by
- A.sufficient carbohydrates but less fats in diet
- B.sufficient carbohydrates and fats but deficient proteins in diet
- C.sufficient vitamins but deficient fats in diet
- D.sufficient fats but deficient vitamins in diet
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Kwashiorkor is a disease of protein deficiency in a child who still gets enough calories. It usually appears when a child is weaned from breast milk onto a starchy diet with little protein.
Read the full explanation →Which one of the following is the correct order of pH for the given substances?
- A.Coffee < Lemon juice < Milk of magnesia < Blood
- B.Milk of magnesia < Blood < Coffee < Lemon juice
- C.Lemon juice < Blood < Coffee < Milk of magnesia
- D.Lemon juice < Coffee < Blood < Milk of magnesia
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Read the full explanation →Which one of the following diseases may be caused by the deficiency of vitamin C?
- A.Rickets
- B.Rabies
- C.Hepatitis
- D.Scurvy
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Scurvy is caused by a lack of vitamin C, or ascorbic acid, which the body needs to make collagen, the protein that holds skin, gums and blood vessels together.
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