Acids, Bases and Salts

9 practice questions on Acids, Bases and Salts for NSEJS, with answers

Shishya's practice questions, written with AI. Each answer was checked by an automated second pass, not by a person.

1. 1.Plaster of Paris should be stored in a moisture-proof container because:

   • (A)It reacts with moisture to form gypsum
   • (B)It decomposes in the presence of moisture
   • (C)It becomes highly acidic with moisture
   • (D)It loses its crystalline structure
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   Answer: (A) It reacts with moisture to form gypsum

   Solution: Plaster of Paris (CaSO₄·½H₂O) reacts with moisture to form gypsum (CaSO₄·2H₂O), which makes it hard and unusable.

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2. 2.Which of the following is the correct chemical formula of baking soda?

   • (A)Na2CO3
   • (B)NaHCO3
   • (C)NaCl
   • (D)NaOH
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   Answer: (B) NaHCO3

   Solution: Baking soda is sodium bicarbonate, which has the chemical formula NaHCO3. Na2CO3 is washing soda, NaCl is common salt, and NaOH is caustic soda. Baking soda is commonly used in cooking and as an antacid.

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3. 3.A solution turns red litmus blue and has a pH of 12. This solution is most likely:

   • (A)Lemon juice
   • (B)Dilute hydrochloric acid
   • (C)Sodium hydroxide solution
   • (D)Pure water
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   Answer: (C) Sodium hydroxide solution

   Solution: A solution that turns red litmus blue is basic in nature. A pH of 12 indicates a strong base. Among the options, sodium hydroxide (NaOH) is a strong base with pH around 12-14. Lemon juice and dilute HCl are acidic, and pure water has pH 7.

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4. 4.A student tested the pH of rainwater collected from an industrial area and found it to be 4.5. If this rainwater is neutralized by adding a certain amount of baking soda (NaHCO₃), what will be the expected change in pH?

   • (A)pH will decrease further
   • (B)pH will increase towards 7
   • (C)pH will remain unchanged
   • (D)pH will become exactly 14
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   Answer: (B) pH will increase towards 7

   Solution: Baking soda (NaHCO₃) is a weak base. When added to acidic rainwater (pH 4.5), it neutralizes the acid and increases the pH towards neutral (7).

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5. 5.When dilute sulphuric acid is poured on a copper plate, the gas evolved is:

   • (A)Hydrogen gas
   • (B)Carbon dioxide gas
   • (C)Sulphur dioxide gas
   • (D)No gas is evolved
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   Answer: (D) No gas is evolved

   Solution: Copper is less reactive than hydrogen in the reactivity series. Therefore, dilute sulphuric acid cannot displace copper to form hydrogen gas. No reaction occurs between dilute sulphuric acid and copper metal at room temperature, so no gas is evolved.

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6. 6.In the chlor-alkali process, sodium hydroxide is formed at the:

   • (A)Anode
   • (B)Cathode
   • (C)Both anode and cathode
   • (D)In the bulk of the solution
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   Answer: (B) Cathode

   Solution: In the chlor-alkali process, brine (NaCl solution) is electrolysed. At the cathode, water is reduced to produce hydrogen gas and hydroxide ions. These hydroxide ions combine with sodium ions to form NaOH near the cathode. Chlorine gas is produced at the anode.

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7. 7.A farmer's field has soil with pH 4.2. To improve crop yield, he should add:

   • (A)Ammonium sulphate fertilizer
   • (B)Quicklime (calcium oxide)
   • (C)Organic compost with pH 5.5
   • (D)Dilute sulphuric acid
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   Answer: (B) Quicklime (calcium oxide)

   Solution: Soil with pH 4.2 is highly acidic. To neutralize acidic soil, a base must be added. Quicklime (CaO) is a basic substance that reacts with soil acids to increase the pH towards neutral. Ammonium sulphate is an acidic fertilizer, and dilute acid would make soil more acidic.

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8. 8.Bleaching powder gradually loses its bleaching power when kept in open. This is because it reacts with which atmospheric component?

   • (A)Nitrogen, forming calcium nitrate
   • (B)Carbon dioxide, releasing chlorine gas
   • (C)Oxygen, forming calcium oxide
   • (D)Water vapour, forming calcium hydroxide only
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   Answer: (B) Carbon dioxide, releasing chlorine gas

   Solution: Bleaching powder (CaOCl2) reacts with atmospheric carbon dioxide to form calcium carbonate and releases chlorine gas. The reaction is: CaOCl2 + CO2 → CaCO3 + Cl2. As chlorine escapes, the bleaching power is lost because chlorine is the active bleaching agent in bleaching powder.

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9. 9.When crystals of washing soda are left exposed to air, they:

   • (A)Absorb moisture and become liquid
   • (B)Lose water of crystallisation and become powdery
   • (C)React with oxygen and turn yellow
   • (D)Remain unchanged
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   Answer: (B) Lose water of crystallisation and become powdery

   Solution: Washing soda (Na2CO3.10H2O) contains 10 molecules of water of crystallisation. When exposed to dry air, it loses this water of crystallisation through efflorescence and becomes anhydrous sodium carbonate (Na2CO3), which is a white powder.

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