In its new sample paper for 2026 board exam class 10, CBSE has made big changes. Now they are asking conceptual questions for 1 marks, 2 marks, 3 marks, 4 marks, and 5 marks.
“Acids Bases And Salts 3 Marks Questions Answers” is designed to help you practice effectively and confidently tackle exam questions.
Read our short notes and MCQs for better preparation.
Chemical Properties of Acids and Bases
- An element ‘X’ reacts with dilute hydrochloric acid to produce a gas that burns with a pop sound.
(i) Identify the gas evolved.
(ii) Write a balanced chemical equation for the reaction if ‘X’ is zinc.
(iii) Why is this reaction classified as a displacement reaction?
Answer:
(i) Hydrogen gas is evolved.
(ii) Zn(s) + 2HCl(aq) → ZnCl₂(aq) + H₂(g)
(iii) Because the metal displaces hydrogen atoms from the acid as hydrogen gas and forms a salt, it is a displacement reaction.
(Source: Acids, Bases and Salts , p. 20)
- A student added dilute sulphuric acid to sodium carbonate in a test tube.
(i) What gas is evolved?
(ii) How will you test the presence of this gas?
(iii) Write the balanced chemical equation for the reaction.
Answer:
(i) Carbon dioxide gas is evolved.
(ii) Pass the gas through lime water; it turns milky due to formation of white precipitate of calcium carbonate.
(iii) Na₂CO₃(s) + H₂SO₄(aq) → Na₂SO₄(aq) + H₂O(l) + CO₂(g)
(Source: Acids, Bases and Salts , p. 21)
- A metal compound ‘A’ reacts with dilute HCl to produce effervescence. The gas evolved extinguishes a burning candle and forms a white precipitate with lime water. One of the products is calcium chloride.
(i) Identify compound ‘A’.
(ii) Write the balanced chemical equation.
(iii) What is the common name of compound ‘A’?
Answer:
(i) Compound ‘A’ is calcium carbonate.
(ii) CaCO₃(s) + 2HCl(aq) → CaCl₂(aq) + H₂O(l) + CO₂(g)
(iii) Common name is limestone/chalk/marble.
(Source: Acids, Bases and Salts , p. 21)
- A student added sodium hydroxide solution to zinc granules and warmed the mixture.
(i) What gas is evolved?
(ii) Write the chemical equation for the reaction.
(iii) Why is this reaction not possible with all metals?
Answer:
(i) Hydrogen gas is evolved.
(ii) 2NaOH(aq) + Zn(s) → Na₂ZnO₂(s) + H₂(g)
(iii) Because such reactions are not possible with all metals—only amphoteric metals like zinc react with bases.
(Source: Acids, Bases and Salts , p. 20)
- Copper oxide is added to dilute hydrochloric acid.
(i) What is the colour of the resulting solution?
(ii) Name the salt formed.
(iii) Write the balanced chemical equation.
Answer:
(i) The solution becomes blue-green.
(ii) Copper(II) chloride is formed.
(iii) CuO(s) + 2HCl(aq) → CuCl₂(aq) + H₂O(l)
(Source: Acids, Bases and Salts , p. 21)
Reaction of Non-metallic Oxides with Bases
- Carbon dioxide is passed through calcium hydroxide solution.
(i) What is observed?
(ii) What happens when excess CO₂ is passed?
(iii) Write both chemical equations.
Answer:
(i) Lime water turns milky due to white precipitate of CaCO₃.
(ii) Milkiness disappears as insoluble calcium carbonate converts to water soluble calcium bicarbonate.
(iii)
Ca(OH)₂(aq) + CO₂(g) → CaCO₃(s) + H₂O(l)
CaCO₃(s) + H₂O(l) + CO₂(g) → Ca(HCO₃)₂(aq)
(Source: Acids, Bases and Salts , p. 21)
Neutralisation Reactions
- A student added dilute NaOH to dilute HCl dropwise using phenolphthalein as indicator.
(i) What colour change is observed at the endpoint?
(ii) What type of reaction is this?
(iii) Write the balanced chemical equation.
Answer:
(i) Solution changes from pink to colourless.
(ii) It is a neutralisation reaction.
(iii) NaOH(aq) + HCl(aq) → NaCl(aq) + H₂O(l)
(Source: Acids, Bases and Salts , p. 21)
- A farmer finds that the pH of his soil is 4.5.
(i) Is the soil acidic or basic?
(ii) Name two substances he can add to neutralise it.
(iii) What is the chemical name of slaked lime?
Answer:
(i) The soil is acidic.
(ii) He can add quick lime (calcium oxide), slaked lime (calcium hydroxide) or chalk (calcium carbonate).
(iii) Calcium hydroxide.
(Source: Acids, Bases and Salts , p. 28)
pH and Importance in Everyday Life
- The pH of rainwater in an industrial area is found to be 4.8.
(i) What is this type of rain called?
(ii) Why is it harmful to aquatic life?
(iii) What is the normal pH range for survival of living organisms?
Answer:
(i) It is called acid rain.
(ii) It lowers the pH of river water, making survival of aquatic life difficult.
(iii) Living organisms survive in a narrow pH range of 7.0 to 7.8.
(Source: Acids, Bases and Salts , p. 26)
- A person suffers from tooth decay.
(i) What is the pH condition in the mouth that causes decay?
(ii) What substance in tooth enamel gets corroded?
(iii) How can toothpastes prevent decay?
Answer:
(i) Decay starts when pH of the mouth is lower than 5.5.
(ii) Calcium hydroxyapatite (tooth enamel) gets corroded.
(iii) Toothpastes are generally basic and neutralise excess acid, preventing decay.
(Source: Acids, Bases and Salts , p. 27)
- A person is stung by a bee.
(i) What acid is injected?
(ii) Suggest a household remedy.
(iii) What is the nature of the remedy?
Answer:
(i) Methanoic acid is injected.
(ii) Apply baking soda.
(iii) It is a mild base.
(Source: Acids, Bases and Salts , p. 27)
Indicators
- A student tested four solutions with red litmus paper. Only one turned it blue.
(i) What does this indicate about that solution?
(ii) Name two synthetic indicators.
(iii) Name two natural indicators.
Answer:
(i) It is basic in nature.
(ii) Methyl orange and phenolphthalein.
(iii) Litmus and turmeric.
(Source: Acids, Bases and Salts , p. 18)
- A curry stain on white cloth turns reddish-brown when washed with soap.
(i) Why does this happen?
(ii) Why does it turn yellow again on rinsing with water?
(iii) What does this indicate about turmeric?
Answer:
(i) Because soap is basic and turmeric (in curry) acts as an indicator.
(ii) Excess base is removed, restoring original colour.
(iii) Turmeric is a natural acid-base indicator.
(Source: Acids, Bases and Salts , p. 18)
Olfactory Indicators
- A student added dilute HCl to vanilla essence.
(i) What change is observed in odour?
(ii) What happens when NaOH is added instead?
(iii) What are such substances called?
Answer:
(i) Odour of vanilla is not detected in acidic medium.
(ii) Odour is retained in basic medium.
(iii) They are called olfactory indicators.
(Source: Acids, Bases and Salts , p. 19)
Conductivity of Acids and Bases
- A circuit with a bulb and two electrodes is dipped in HCl solution—the bulb glows. But it does not glow in glucose solution.
(i) Why does the bulb glow in HCl?
(ii) Why not in glucose?
(iii) What ions are responsible for conductivity in acids?
Answer:
(i) Because HCl produces H⁺(aq) and Cl⁻(aq) ions, which conduct electricity.
(ii) Glucose does not produce ions in solution.
(iii) H⁺(aq) ions (or H₃O⁺ ions) are responsible.
(Source: Acids, Bases and Salts , p. 22–23)
- Dry HCl gas is passed over dry blue litmus paper.
(i) Does the colour change?
(ii) What happens if the litmus is moist?
(iii) What does this prove?
Answer:
(i) No colour change.
(ii) Turns red.
(iii) Acids produce H⁺ ions only in aqueous solution; dry HCl has no acidic character.
(Source: Acids, Bases and Salts , p. 23)
Dilution
- While diluting concentrated H₂SO₄, a student added water to acid.
(i) What danger does this pose?
(ii) What is the correct procedure?
(iii) Why is the process exothermic?
Answer:
(i) Heat generated may cause splashing and burns; glass may break.
(ii) Always add acid slowly to water with constant stirring.
(iii) Because dissolving acid in water is a highly exothermic process.
(Source: Acids, Bases and Salts , p. 24)
Strength of Acids and Bases
- Equal concentrations of HCl and CH₃COOH are taken.
(i) Which produces more H⁺ ions?
(ii) Which is a strong acid?
(iii) What determines the strength of an acid?
Answer:
(i) HCl produces more H⁺ ions.
(ii) HCl is a strong acid.
(iii) Number of H⁺ ions produced determines strength.
(Source: Acids, Bases and Salts , p. 26)
Salts – Family and pH
- The following salts are given: NaCl, Na₂SO₄, KCl, CuSO₄.
(i) Identify two salts belonging to the sodium family.
(ii) Identify two salts belonging to the chloride family.
(iii) Which salt is neutral, acidic, and basic respectively?
Answer:
(i) NaCl and Na₂SO₄.
(ii) NaCl and KCl.
(iii) NaCl – neutral, CuSO₄ – acidic, Na₂CO₃ – basic (if included).
(Source: Acids, Bases and Salts , p. 29)
- A salt solution turns red litmus blue.
(i) Is the salt acidic or basic?
(ii) What kind of acid and base formed it?
(iii) Give an example.
Answer:
(i) The salt is basic.
(ii) Formed from strong base and weak acid.
(iii) Sodium carbonate (Na₂CO₃).
(Source: Acids, Bases and Salts , p. 29)
Common Salt and Derivatives
- Electricity is passed through aqueous NaCl (brine).
(i) Name the three products formed.
(ii) What is this process called?
(iii) Write the balanced equation.
Answer:
(i) Sodium hydroxide, chlorine gas, hydrogen gas.
(ii) Chlor-alkali process.
(iii) 2NaCl(aq) + 2H₂O(l) → 2NaOH(aq) + Cl₂(g) + H₂(g)
(Source: Acids, Bases and Salts , p. 30)
- Chlorine gas is passed over dry slaked lime.
(i) What product is formed?
(ii) Write its chemical formula.
(iii) Give one use.
Answer:
(i) Bleaching powder.
(ii) CaOCl₂.
(iii) Used for bleaching cotton or disinfecting drinking water.
(Source: Acids, Bases and Salts , p. 31)
- Baking soda is heated during cooking.
(i) What products are formed?
(ii) Write the equation.
(iii) Why is it used in baking powder?
Answer:
(i) Sodium carbonate, water, carbon dioxide.
(ii) 2NaHCO₃ → Na₂CO₃ + H₂O + CO₂
(iii) CO₂ makes bread/cake soft and spongy.
(Source: Acids, Bases and Salts , p. 31)
- Washing soda is used to treat hard water.
(i) What is its chemical name?
(ii) Write its formula.
(iii) What does 10H₂O signify?
Answer:
(i) Sodium carbonate decahydrate.
(ii) Na₂CO₃·10H₂O.
(iii) It indicates water of crystallisation—10 water molecules per formula unit.
(Source: Acids, Bases and Salts , p. 32)
Water of Crystallisation
- Blue crystals of copper sulphate are heated in a boiling tube.
(i) What colour change is observed?
(ii) What appears on the cooler parts of the tube?
(iii) What is the chemical formula of hydrated copper sulphate?
Answer:
(i) Turns white.
(ii) Water droplets appear.
(iii) CuSO₄·5H₂O.
(Source: Acids, Bases and Salts , p. 32; Fig. 2.9)
- Water is added to anhydrous copper sulphate.
(i) What is observed?
(ii) What does this prove?
(iii) What is “water of crystallisation”?
Answer:
(i) Blue colour is restored.
(ii) Proves that water was part of the crystal structure.
(iii) It is the fixed number of water molecules present in one formula unit of a salt.
(Source: Acids, Bases and Salts , p. 32)
- Gypsum is heated at 373 K.
(i) What is formed?
(ii) Write its chemical formula.
(iii) Why is it called Plaster of Paris?
Answer:
(i) Plaster of Paris.
(ii) CaSO₄·½H₂O.
(iii) Because large deposits were found in Paris.
(Source: Acids, Bases and Salts , p. 32–33)
- Plaster of Paris is mixed with water.
(i) What is formed?
(ii) Write the equation.
(iii) Why must it be stored in a moisture-proof container?
Answer:
(i) Gypsum (hard solid mass).
(ii) CaSO₄·½H₂O + 1½H₂O → CaSO₄·2H₂O
(iii) Because it absorbs moisture and sets into a hard mass.
(Source: Acids, Bases and Salts , p. 33)
Indicators and pH Testing
- A student tested lemon juice, NaOH, and NaCl with pH paper.
(i) What approximate pH values would be observed?
(ii) Which is acidic, basic, and neutral?
(iii) What colour would universal indicator show for each?
Answer:
(i) Lemon juice: ~2, NaOH: ~14, NaCl: 7.
(ii) Lemon juice – acidic, NaOH – basic, NaCl – neutral.
(iii) Red/orange, purple, green respectively.
(Source: Acids, Bases and Salts , p. 26; Fig. 2.7)
- Soil from a field is mixed with water and filtered. The filtrate turns pH paper yellow-orange.
(i) What is the approximate pH?
(ii) Is the soil acidic or basic?
(iii) Which crops may not grow well?
Answer:
(i) pH < 7 (approx. 5–6).
(ii) Acidic.
(iii) Crops requiring neutral or basic soil may not grow well.
(Source: Acids, Bases and Salts , p. 27)
Antacids and Digestion
- A person takes baking soda for acidity.
(i) Why is it effective?
(ii) What type of salt is baking soda?
(iii) Give another use of baking soda.
Answer:
(i) It is mildly basic and neutralises excess stomach acid.
(ii) Mild non-corrosive basic salt.
(iii) Used in soda-acid fire extinguishers or baking powder.
(Source: Acids, Bases and Salts , p. 31)
Reactions with Metals
- Why should curd not be stored in copper vessels?
Answer:
Because curd contains acids which react with copper to form toxic compounds.
(Source: Acids, Bases and Salts , p. 22, Q2)
Electrolysis
- Amrita used distilled water for electrolysis, but the bulb did not glow.
(i) Why?
(ii) What did she add to make it work?
(iii) What gases are produced at electrodes?
Answer:
(i) Distilled water does not conduct electricity as it has no ions.
(ii) She added a few drops of acid or base (e.g., dilute H₂SO₄).
(iii) Hydrogen at cathode, oxygen at anode.
(Source: Acids, Bases and Salts , p. 22; Fig. 2.3)
Natural Acids
- Name the acid present in :
(i) Vinegar – ?
(ii) Ant sting – ?
(iii) Tomato – ?
Answer:
(i) Acetic acid
(ii) Methanoic acid
(iii) Oxalic acid
(Source: Acids, Bases and Salts , p. 28; Table 2.3)
pH Scale
- Two solutions A (pH=3) and B (pH=10).
(i) Which has higher H⁺ concentration?
(ii) Which is acidic and which is basic?
(iii) What is the nature of a solution with pH=7?
Answer:
(i) Solution A.
(ii) A – acidic, B – basic.
(iii) Neutral.
(Source: Acids, Bases and Salts , p. 25)
Household Applications
- Why is washing soda used for cleaning?
Answer:
Because it is a basic salt and removes dirt by saponification of oils.
(Source: Acids, Bases and Salts , p. 32)
- How does baking powder work in cakes?
Answer:
It contains baking soda and tartaric acid; when heated or mixed with water, CO₂ is released, making cake soft and spongy.
(Source: Acids, Bases and Salts , p. 31)
Neutralisation in Nature
- A person touches nettle leaves and gets stung.
(i) What acid is injected?
(ii) What traditional remedy is used?
(iii) What is the nature of dock plant?
Answer:
(i) Methanoic acid.
(ii) Rub with dock plant leaf.
(iii) Basic in nature.
(Source: Acids, Bases and Salts , p. 28)
Industrial Use
- Name three uses of chlorine obtained from chlor-alkali process.
Answer:
(i) Manufacture of bleaching powder
(ii) Disinfecting drinking water
(iii) Production of PVC and solvents
(Source: Acids, Bases and Salts , p. 30–31; Fig. 2.8)
Riya performed an experiment to test the conductivity of different solutions. She set up a circuit with a battery, bulb, and two electrodes, as shown in Fig. 2.3. She tested distilled water, dilute HCl, and sugar solution one by one. The bulb glowed only in dilute HCl.
A. Why did the bulb not glow in distilled water?
B. Why did it glow in dilute HCl but not in sugar solution?
C. What type of ions are responsible for conduction in acids?
Answer:
A. Because distilled water does not contain ions and hence does not conduct electricity.
B. Dilute HCl produces H⁺(aq) and Cl⁻(aq) ions, which conduct electricity, whereas sugar does not dissociate into ions in solution.
C. H⁺(aq) ions (or hydronium ions, H₃O⁺) are responsible for conduction in acids.
(Source: Acids, Bases and Salts , p. 22–23; Fig. 2.3)
Aditya added a few drops of vanilla essence to two test tubes—A containing dilute NaOH and B containing dilute HCl. He noticed that the odour of vanilla disappeared in test tube B but remained in A.
A. What is the name given to substances like vanilla essence in this context?
B. Why did the odour disappear in acidic medium?
C. Name two other substances that can act similarly.
Answer:
A. They are called olfactory indicators.
B. Because in acidic medium, the odour of vanilla is not detected.
C. Onion and clove oil.
(Source: Acids, Bases and Salts , p. 19; Activity 2.2)
Priya heated blue crystals of copper sulphate in a dry boiling tube as shown in Fig. 2.9. She observed that the colour changed to white and water droplets appeared on the cooler parts of the tube.
A. What is the chemical name of the blue crystals?
B. What do the water droplets indicate?
C. What is meant by “water of crystallisation”?
Answer:
A. Hydrated copper sulphate or copper sulphate pentahydrate.
B. They indicate that water was present as water of crystallisation in the crystal structure.
C. It is the fixed number of water molecules present in one formula unit of a salt.
(Source: Acids, Bases and Salts , p. 32; Fig. 2.9)
Karan tested lemon juice, baking soda solution, and NaCl solution with pH paper. The colours obtained were red, green, and blue respectively.
A. What is the approximate pH of each solution?
B. Which solution is acidic, basic, and neutral?
C. Why is pH important in tooth decay?
Answer:
A. Lemon juice: ~2, NaCl: 7, baking soda: ~9.
B. Lemon juice – acidic, baking soda – basic, NaCl – neutral.
C. Tooth decay starts when pH in the mouth falls below 5.5, causing enamel to corrode.
(Source: Acids, Bases and Salts , p. 26–27; Fig. 2.7)
Meera added zinc granules to dilute NaOH and warmed the mixture. She collected the gas evolved and brought a burning splinter near it—it burnt with a pop sound.
A. Identify the gas evolved.
B. Write the balanced chemical equation.
C. Why don’t all metals react with bases?
Answer:
A. Hydrogen gas.
B. 2NaOH(aq) + Zn(s) → Na₂ZnO₂(aq) + H₂(g)
C. Because only amphoteric metals like zinc react with bases; most metals do not.
(Source: Acids, Bases and Salts , p. 20; Activity 2.4)
Suman passed CO₂ gas through lime water. The solution turned milky. On passing excess CO₂, the milkiness disappeared.
A. Why did the solution turn milky initially?
B. Why did the milkiness disappear on excess CO₂?
C. Write both chemical equations involved.
Answer:
A. Due to formation of insoluble white precipitate of calcium carbonate.
B. Because CaCO₃ reacts with excess CO₂ and water to form soluble calcium bicarbonate.
C.
Ca(OH)₂(aq) + CO₂(g) → CaCO₃(s) + H₂O(l)
CaCO₃(s) + H₂O(l) + CO₂(g) → Ca(HCO₃)₂(aq)
(Source: Acids, Bases and Salts , p. 21)
Rahul was stung by a bee while gardening. His mother applied a paste of baking soda on the affected area, and the pain reduced.
A. What acid is injected during a bee sting?
B. Why does baking soda provide relief?
C. Name another natural sting that injects the same acid.
Answer:
A. Methanoic acid.
B. Because baking soda is a mild base that neutralises the acid.
C. Nettle leaf sting.
(Source: Acids, Bases and Salts , p. 27–28; Table 2.3)
Ananya electrolysed water using the setup in Fig. 2.3, but the bulb did not glow. She then added a few drops of dilute sulphuric acid, and the bulb glowed.
A. Why did the bulb not glow initially?
B. Why did it glow after adding acid?
C. Name the gases produced at the cathode and anode.
Answer:
A. Because pure water has no ions and does not conduct electricity.
B. Acid provides H⁺ and SO₄²⁻ ions, enabling conduction.
C. Hydrogen at cathode, oxygen at anode.
(Source: Acids, Bases and Salts , p. 22–23; Fig. 2.3)
Vikas added dilute HCl to a compound ‘X’. A gas was evolved that turned lime water milky and extinguished a burning candle. One product was CaCl₂.
A. Identify compound ‘X’.
B. Write the balanced equation.
C. What is the common name of ‘X’?
Answer:
A. Calcium carbonate.
B. CaCO₃(s) + 2HCl(aq) → CaCl₂(aq) + H₂O(l) + CO₂(g)
C. Limestone, chalk, or marble.
(Source: Acids, Bases and Salts , p. 21; Q3, p. 22)
Neha stored curd in a copper bowl overnight. The next day, the curd had a bitter taste and greenish tint.
A. Why should curd not be stored in copper vessels?
B. What type of reaction occurs?
C. Name two other sour substances that should not be stored in metal containers.
Answer:
A. Because curd contains acids that react with copper to form toxic compounds.
B. Acid-metal reaction (displacement).
C. Lemon juice and vinegar.
(Source: Acids, Bases and Salts , p. 22; Q1)
A farmer tested his field soil and found its pH to be 4.2. He decided to add slaked lime to the soil.
A. Why is the soil unsuitable for most crops?
B. How does slaked lime help?
C. What is the chemical name of slaked lime?
Answer:
A. Because most plants grow best in neutral or slightly acidic soil (pH 6–7); pH 4.2 is too acidic.
B. Slaked lime is basic and neutralises excess acid in the soil.
C. Calcium hydroxide.
(Source: Acids, Bases and Salts , p. 28; Q4)
Ritu heated baking soda in a test tube. She passed the gas evolved through lime water, which turned milky.
A. Name the gas evolved.
B. Write the chemical equation for the decomposition.
C. Why is baking soda used in baking powder?
Answer:
A. Carbon dioxide.
B. 2NaHCO₃(s) → Na₂CO₃(s) + H₂O(g) + CO₂(g)
C. Because CO₂ makes bread or cake soft and spongy.
(Source: Acids, Bases and Salts , p. 31)
A student added dry HCl gas to dry blue litmus paper—no colour change occurred. But when moist litmus paper was used, it turned red.
A. Why no change with dry litmus?
B. What does this prove about acidic character?
C. Write the ionic reaction when HCl dissolves in water.
Answer:
A. Because dry HCl gas does not produce H⁺ ions.
B. That acids produce H⁺ ions only in aqueous solution.
C. HCl + H₂O → H₃O⁺ + Cl⁻
(Source: Acids, Bases and Salts , p. 23; Activity 2.9)
Gypsum is heated at 373 K to make Plaster of Paris, which is used by doctors.
A. Write the chemical formula of gypsum and Plaster of Paris.
B. Why must Plaster of Paris be stored in a moisture-proof container?
C. Why is it called “Plaster of Paris”?
Answer:
A. Gypsum: CaSO₄·2H₂O; Plaster of Paris: CaSO₄·½H₂O
B. Because it reacts with moisture to form hard gypsum.
C. Because large deposits were found in Paris.
(Source: Acids, Bases and Salts , p. 32–33)
During the chlor-alkali process, electricity is passed through brine. Three useful products are formed.
A. Name the three products.
B. Write the balanced chemical equation.
C. Give one use of chlorine gas.
Answer:
A. Sodium hydroxide, chlorine gas, hydrogen gas.
B. 2NaCl(aq) + 2H₂O(l) → 2NaOH(aq) + Cl₂(g) + H₂(g)
C. Used for disinfecting drinking water or making bleaching powder.
(Source: Acids, Bases and Salts , p. 30; Fig. 2.8)
