🧪 Class 10 – Acids, Bases and Salts MCQ Quiz
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🧠 Multiple Choice Questions (20)
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1. What is the main function of an indicator in a solution?
Indicators show whether a solution is acidic or basic by changing colour or smell.
Natural, synthetic and olfactory indicators all help us identify acids and bases without tasting them.
Litmus, turmeric, phenolphthalein and methyl orange are common indicators used in school labs.
2. Turmeric paper in a basic solution shows which colour?
In basic medium, turmeric turns red.
Turmeric is a natural indicator. It shows no change in acidic solution but becomes reddish brown in bases.
You can test soap (basic) and lemon juice (acidic) at home using turmeric paste.
3. Which one is an olfactory indicator?
Vanilla is an example of an olfactory indicator.
Olfactory indicators show a change in smell in acidic and basic solutions instead of colour change.
Onion and clove oil are also used as olfactory indicators in experiments.
4. Which statement about dilute and concentrated acids is correct?
Dilute acid: small amount of acid in large amount of water. Concentrated acid: large amount of acid in small amount of water.
Dilution reduces the concentration of H₃O⁺ ions per unit volume, making the acid less corrosive.
Always add acid to water, never water to concentrated acid, to avoid violent splashing.
5. Which ion is responsible for the acidic nature of acids?
Acids show their acidic properties due to the presence of H⁺ (or H₃O⁺) ions in aqueous solution.
H⁺ ions cannot exist alone in water and are present as hydronium ions (H₃O⁺).
All hydrogen-containing compounds are not acids; for example, glucose and alcohol do not give H⁺ ions in water.
6. What is the general reaction of a dilute acid with a metal?
Dilute acid reacts with a metal to form a salt and hydrogen gas.
Example: 2HCl + Zn → ZnCl₂ + H₂. The gas can be tested by the pop test using a burning matchstick.
Hydrogen gas burns with a characteristic ‘pop’ sound.
7. What happens when carbon dioxide gas is passed through lime water for a long time?
Lime water first turns milky and then becomes clear again.
CO₂ + Ca(OH)₂ → CaCO₃ (milky) + H₂O, and on excess CO₂, CaCO₃ dissolves forming soluble Ca(HCO₃)₂.
This is a common test for CO₂ in school chemistry labs.
8. Metal oxides are generally:
Metal oxides are generally basic.
They react with acids to form salt and water. Example: CuO + 2HCl → CuCl₂ + H₂O.
Some metal oxides like Al₂O₃ and ZnO are amphoteric (react with both acids and bases).
9. Which ion is responsible for the basic character of bases?
Bases show basic properties due to the presence of OH⁻ ions in aqueous solution.
NaOH, KOH, Ca(OH)₂, etc., dissociate to give hydroxide ions which are responsible for basic nature.
Soluble bases are called alkalis (e.g., NaOH, KOH).
10. What is a neutralisation reaction?
In neutralisation, an acid reacts with a base to form salt and water.
Example: HCl + NaOH → NaCl + H₂O. The acidic and basic properties cancel each other.
Antacids neutralise excess HCl in the stomach and give relief from acidity.
11. Which acid is produced in our stomach to help digestion?
The stomach secretes hydrochloric acid (HCl).
HCl helps in digesting food and killing harmful bacteria. Excess HCl causes acidity.
Antacids like milk of magnesia are basic and neutralise excess stomach acid.
12. In CuSO₄·5H₂O, “5H₂O” represents:
5H₂O represents water of crystallisation.
Water of crystallisation is the fixed number of water molecules present in one formula unit of a salt.
Blue crystals of CuSO₄·5H₂O turn white on heating as water of crystallisation is lost.
13. Which gas turns lime water milky?
Carbon dioxide (CO₂) gas turns lime water milky.
This is due to formation of insoluble calcium carbonate: Ca(OH)₂ + CO₂ → CaCO₃ + H₂O.
On passing excess CO₂, the milkiness disappears because CaCO₃ converts to soluble Ca(HCO₃)₂.
14. Which of the following is a strong base?
Sodium hydroxide (NaOH) is a strong base.
Strong bases completely ionise in water to give a large number of OH⁻ ions.
NaOH is also called caustic soda and is used in the manufacture of soaps.
15. Which pH value represents a strongly acidic solution?
pH = 1 indicates a strongly acidic solution.
Lower pH (<7) means more H⁺ ion concentration; higher pH (>7) means basic solution.
Universal indicator and pH paper help us estimate the pH of a solution quickly.
16. Rain with pH less than 5.6 is called:
Rain with pH < 5.6 is called acid rain.
Acid rain lowers the pH of river and lake water and harms aquatic life, soil and monuments.
Burning fossil fuels releases SO₂ and NO₂ which form acids in the atmosphere and cause acid rain.
17. Which salt is used to remove permanent hardness of water?
Washing soda (Na₂CO₃·10H₂O) is used to remove permanent hardness of water.
It reacts with Ca²⁺ and Mg²⁺ ions to form insoluble carbonates and softens the water.
Washing soda is also used in glass, soap and paper industries.
18. Which of the following is a neutral salt?
Sodium chloride (NaCl) is a neutral salt.
It is formed from a strong acid (HCl) and a strong base (NaOH), so its aqueous solution has pH ≈ 7.
NaCl is the common salt used in our food and as raw material for many chemicals.
19. Which chemical is used for disinfecting drinking water?
Bleaching powder (CaOCl₂) is used to disinfect drinking water.
It releases chlorine which kills germs in water.
Bleaching powder is also used for bleaching cotton, linen and wood pulp.
20. Which of the following statements about Plaster of Paris (POP) is correct?
POP is obtained by heating gypsum and is used for plastering fractured bones and making models.
Gypsum (CaSO₄·2H₂O) on heating at about 373 K forms CaSO₄·½H₂O (Plaster of Paris).
If gypsum is overheated, it becomes dead burnt plaster (anhydrous CaSO₄) which has no setting property.