Class X Science
Chapter 2 – Acids, Bases and Salts
NCERT Solutions (Concise and exam-oriented)
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Questions from the Textbook
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Q1. Why should curd and sour substances not be kept in brass and copper vessels?
Answer:
Curd and sour substances contain acids. These acids react with copper and brass to form poisonous salts, which can cause food poisoning.
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Q2. Which gas is usually liberated when an acid reacts with a metal?
How will you test this gas?
Answer:
The gas is hydrogen.
It is tested by the pop sound produced when a burning matchstick is brought near the gas.
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Q3. Metal compound A reacts with dilute hydrochloric acid to produce carbon dioxide.
Which compound is A?
Answer:
The compound A is a metal carbonate or metal hydrogen carbonate.
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Q4. Why does dry hydrogen chloride gas not change the colour of dry litmus paper?
Answer:
Dry HCl gas does not produce hydrogen ions in the absence of water.
Without water, it does not show acidic behaviour.
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Q5. Why should an aqueous solution of an acid be diluted by adding water to the acid and not the acid to water?
Answer:
Because adding acid to water slowly prevents splashing and excessive heat.
Adding water to concentrated acid may cause serious burns.
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Q6. How is the concentration of hydronium ions (H₃O⁺) affected when a solution of an acid is diluted?
Answer:
The concentration of hydronium ions decreases on dilution.
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Q7. How is the concentration of hydroxide ions (OH⁻) affected when excess base is dissolved in a solution of sodium hydroxide?
Answer:
The concentration of hydroxide ions increases.
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Q8. You have two solutions, A and B. The pH of A is 6 and the pH of B is 8.
Which solution has more hydrogen ion concentration?
Answer:
Solution A has more hydrogen ion concentration.
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Q9. What effect does the concentration of H⁺ (aq) ions have on the nature of a solution?
Answer:
Higher H⁺ concentration → more acidic solution.
Lower H⁺ concentration → less acidic solution.
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Q10. Do basic solutions also have H⁺ (aq) ions?
Why are they basic then?
Answer:
Yes, basic solutions also contain H⁺ ions.
They are basic because the concentration of OH⁻ ions is much higher than that of H⁺ ions.
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In-text Questions – Salts
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Q11. Why does an aqueous solution of sodium carbonate turn red litmus blue?
Answer:
Because sodium carbonate is a basic salt.
It produces OH⁻ ions in water.
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Q12. Why is plaster of Paris stored in moisture-proof containers?
Answer:
Because it reacts with moisture and changes into gypsum, becoming useless.
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Very Important NCERT Questions
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Q13. Write the chemical name and formula of plaster of Paris.
Answer:
Calcium sulphate hemihydrate
Formula: CaSO₄·½H₂O
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Q14. Write the chemical name and formula of washing soda.
Answer:
Sodium carbonate decahydrate
Formula: Na₂CO₃·10H₂O
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Short Answer Questions
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Q15. What is neutralisation?
Answer:
The reaction between an acid and a base to form salt and water is called neutralisation.
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Q16. Why are antacids used?
Answer:
They neutralise excess acid in the stomach and give relief from acidity.
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Long Answer Type
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Q17. Write the process of preparation of washing soda.
Answer:
Washing soda is prepared from sodium chloride by the Solvay process.
Sodium hydrogen carbonate is first formed, which on heating gives sodium carbonate.
Sodium carbonate crystallises with water to form washing soda.
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Q18. Write two important uses of:
(a) Washing soda
Answer:
1. Used in glass, soap and paper industries
2. Used to remove permanent hardness of water
(b) Plaster of Paris
Answer:
1. Used to make moulds, toys and decorative items
2. Used for plastering fractured bones
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Q19. What is pH? What is its importance?
Answer:
pH is a scale used to measure the acidity or basicity of a solution.
It helps us to know how strong an acid or base is and plays an important role in soil treatment, digestion and environmental studies.
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Q20. Why is tooth decay more common when the pH of the mouth is lower than 5.5?
Answer:
At low pH, acids produced by bacteria damage the enamel of teeth, causing tooth decay.
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