Important Questions for Class 10 Science Chapter 2: Acids, Bases and Salts

Acids produce H+ ions in aqueous solution, bases produce OH- ions, and salts form when acids and bases neutralise each other. Chapter 2 covers indicators, chemical properties, the pH scale, common salt products such as baking soda, washing soda, bleaching powder, and Plaster of Paris, and water of crystallisation.

Important Questions Class 10 Science Chapter 2 on this page cover MCQs, short answer, long answer, concept-wise questions, and important reactions. All questions are structured for CBSE 2026 board exam patterns.

A student who memorises all key equations, understands why dry HCl does not affect dry litmus, and can write the chlor-alkali process with all three products and their uses will handle the highest-weightage questions from this chapter. Most marks are lost on equations and on confusing baking soda, washing soda, and bleaching powder. All questions and answers are available section by section below. Also practise Important Questions Class 10 Science Chapter 1 and Important Questions Class 10 Science Chapter 3.

Key Takeaways

Overview of Class 10 Science Chapter 2 Important Questions

Acids bases and salts class 10 important questions with answers on this page cover seven concept clusters: indicators, chemical properties of acids and bases, ions in aqueous solution, pH scale, neutralisation, salts and common salt products, and water of crystallisation. Every board question from this chapter maps to one of these areas.

Science important questions class 10 from Chapter 2 appear across all marks categories in CBSE 2026 papers. One-mark questions test formulas and pH values. Three-mark questions ask for reactions and concept differences. Five-mark questions test preparation, properties, and uses of common salt products.

Important Topics in Class 10 Science Chapter 2

Every board question from this chapter maps to one of these concept clusters. Use this as a checklist before starting practice.

Class 10 Science Chapter 2 MCQs with Answers

These acids bases and salts class 10 important questions in MCQ format cover all seven concept clusters. Each answer includes a one-line explanation to build understanding.

Q1. Which of the following gives CO2 on heating? (a) Slaked lime (b) Quick lime (c) Limestone (d) Soda ash (c) Limestone. CaCO3 decomposes on heating to give CaO and CO2.

Q2. The chemical formula of baking soda is: (a) MgSO4 (b) Na2CO3 (c) NaHCO3 (d) MgCO3 (c) NaHCO3. Baking soda is sodium hydrogencarbonate, a mild non-corrosive basic salt.

Q3. The odour of acetic acid resembles that of: (a) Rose (b) Burning plastic (c) Vinegar (d) Kerosene (c) Vinegar. Acetic acid (CH3COOH) is the acid present in vinegar.

Q4. A drop of liquid sample was put on pH paper and it turned blue. The liquid must be: (a) Lemon juice (b) HCl (c) Sodium bicarbonate (d) Ethanoic acid (c) Sodium bicarbonate. Bases change red litmus to blue; sodium bicarbonate is basic.

Q5. Farmers neutralise the effect of acidity on soil by adding: (a) Slaked lime (b) Gypsum (c) Caustic soda (d) Baking soda (a) Slaked lime. Calcium hydroxide is basic and neutralises acidic soil.

Q6. In CuSO4.5H2O, the water molecules are called: (a) Pure water (b) Water of crystallisation (c) Soda water (d) None of these (b) Water of crystallisation. This is the fixed number of water molecules in one formula unit of a hydrated salt.

Q7. The setting of Plaster of Paris takes place due to: (a) Oxidation (b) Reduction (c) Dehydration (d) Hydration (d) Hydration. Plaster of Paris absorbs water and converts back to gypsum, which hardens.

Q8. Which salt is neutral? (a) NH4Cl (b) CH3COONH4 (c) CH3COONa (d) Na2CO3 (b) CH3COONH4 (Ammonium acetate). Formed by a weak acid and a weak base; pH is neutral.

Q9. If the pH of a solution is 13, it is: (a) Weakly acidic (b) Weakly basic (c) Strongly acidic (d) Strongly basic (d) Strongly basic. pH 13 indicates very high OH- concentration.

Q10. The acid-base indicator extracted from lichen is: (a) Methyl orange (b) Phenolphthalein (c) Litmus (d) Turmeric (c) Litmus. It turns red in acidic and blue in basic solutions.

Q11. Washing soda has the formula: (a) Na2CO3.7H2O (b) Na2CO3.10H2O (c) Na2CO3.H2O (d) Na2CO3 (b) Na2CO3.10H2O. Washing soda is sodium carbonate decahydrate.

Q12. Plaster of Paris hardens by: (a) Giving off CO2 (b) Changing into CaCO3 (c) Combining with water (d) Giving out water (c) Combining with water. CaSO4.½H2O + 1½H2O → CaSO4.2H2O.

Q13. A solution turns red litmus blue. Its pH is likely to be: (a) 1 (b) 4 (c) 5 (d) 10 (d) 10. pH above 7 indicates a basic solution.

Q14. Sodium carbonate reacts with hydrochloric acid to produce: (a) NaCl (b) CO2 (c) H2O (d) All of the above (d) All of the above. Na2CO3 + 2HCl → 2NaCl + CO2 + H2O.

Q15. Which of the following medicines is used for treating indigestion? (a) Antibiotics (b) Analgesic (c) Antacid (d) Antiseptic (c) Antacid. Antacids are basic and neutralise excess acid in the stomach.

Q16. A solution reacts with crushed egg-shells to give a gas that turns lime water milky. The solution contains: (a) NaCl (b) HCl (c) LiCl (d) KCl (b) HCl. Egg-shell is CaCO3. It reacts with HCl to give CO2, which turns lime water milky.

Q17. Which of the following is used to dissolve gold? (a) Hydrochloric acid (b) Sulphuric acid (c) Nitric acid (d) Aqua regia (d) Aqua regia. A mixture of concentrated nitric acid and hydrochloric acid in 1:3 ratio.

Q18. The difference in water molecules between gypsum and Plaster of Paris is: (a) 5/2 (b) 2 (c) 1/2 (d) 3/2 (d) 3/2. Gypsum is CaSO4.2H2O; Plaster of Paris is CaSO4.½H2O. Difference = 2 - ½ = 3/2.

Q19. Sodium carbonate is a basic salt because it is a salt of: (a) Strong acid and strong base (b) Weak acid and weak base (c) Strong acid and weak base (d) Weak acid and strong base (d) Weak acid and strong base. Na2CO3 is formed from carbonic acid (weak) and NaOH (strong).

Q20. Which one of the following can be used as an acid-base indicator by a visually impaired student? (a) Litmus (b) Turmeric (c) Vanilla essence (d) Petunia leaves (c) Vanilla essence. It is an olfactory indicator; its smell changes in acidic and basic conditions.

Acids and Bases in the Laboratory: Short Answer Questions

These acid bases and salts class 10 questions and answers cover indicators and the basic properties of acids and bases. These appear as 1-mark and 2-mark questions in CBSE 2026 board papers.

Q1. Name the acid-base indicator extracted from lichen. Litmus. It is a natural purple dye that turns red in acidic conditions and blue in basic conditions.

Q2. Name two olfactory indicators. Onion and vanilla essence. Their odour changes in the presence of acids or bases.

Q3. What colour does phenolphthalein show in a basic solution? Phenolphthalein shows pink colour in a basic solution. It is colourless in acidic and neutral solutions.

Q4. What is the colour of methyl orange in an acidic solution? Methyl orange turns red in acidic solutions. In basic solutions it is yellow.

Q5. Name two synthetic indicators. Methyl orange and phenolphthalein are synthetic indicators.

Q6. How can you identify an acidic solution using only red litmus paper? Red litmus does not change colour in an acidic solution. It turns blue only in a basic solution. Using both red and blue litmus allows identification: the paper that turns red identifies an acid.

Chemical Properties of Acids and Bases: Short Answer Questions

This is the most tested section in acids bases and salts class 10 important questions. These class 10 science chapter 2 question answer items cover reactions with metals, carbonates, and oxides, which CBSE 2026 tests as 2-mark and 3-mark questions.

Q1. Which gas is generally liberated when an acid reacts with a metal? How will you test for the presence of this gas? Hydrogen gas is liberated. Acid + Metal → Salt + Hydrogen gas. Example: Zn + H2SO4 → ZnSO4 + H2. Hydrogen is tested by bringing a burning candle near the gas: it burns with a pop sound.

Q2. Why should curd and sour substances not be kept in brass and copper vessels? Brass is an alloy of copper and zinc. Acids in curd react with these metals to form poisonous soluble salts. This makes the food harmful for consumption.

Q3. What happens when a metal carbonate reacts with an acid? Metal carbonate + Acid → Salt + Water + CO2. Example: Na2CO3 + 2HCl → 2NaCl + H2O + CO2. The CO2 gas turns lime water milky.

Q4. What happens when a metal hydrogencarbonate reacts with an acid? NaHCO3 + HCl → NaCl + H2O + CO2. The reaction produces carbon dioxide, which turns lime water milky and extinguishes a burning splinter.

Q5. What is a neutralisation reaction? Give two examples. A neutralisation reaction is the reaction between an acid and a base to produce salt and water. NaOH + HCl → NaCl + H2O. KOH + HNO3 → KNO3 + H2O.

Q6. What happens when a metallic oxide reacts with an acid? Metal oxide + Acid → Salt + Water. Example: CuO + H2SO4 → CuSO4 + H2O. The solution turns blue-green due to formation of copper sulphate.

Q7. Why does sodium hydroxide react with zinc but not all metals? Sodium hydroxide reacts with amphoteric metals like zinc: 2NaOH + Zn → Na2ZnO2 + H2. Not all metals are amphoteric, so bases cannot react with all metals.

Q8. Why does distilled water not conduct electricity, whereas rainwater does? Distilled water has no ions and cannot conduct electricity. Rainwater contains dissolved gases and salts that ionise, providing ions that conduct electricity.

Q9. Metal compound A reacts with dilute hydrochloric acid to produce effervescence. The gas evolved extinguishes a burning candle. If one compound formed is calcium chloride, write the balanced equation. A is calcium carbonate (CaCO3). The gas is CO2. CaCO3 + 2HCl → CaCl2 + H2O + CO2.

Q10. Why is acid added to water and not water to acid while diluting? Adding water to a concentrated acid produces a highly exothermic reaction. The heat can cause the mixture to splash and cause severe burns. Adding acid to water slowly allows the heat to be absorbed safely by the larger volume of water.

Q11. Why does an aqueous solution of acid conduct electricity? Acids ionise in water to produce H+ (H3O+) and anions. These ions carry electric current through the solution.

Q12. Why do HCl and HNO3 show acidic character in aqueous solution while alcohol and glucose do not? HCl and HNO3 release H+ ions in water. Alcohol and glucose contain hydrogen but do not ionise in water. Without H+ ions, they show no acidic behaviour.

Q13. Equal lengths of magnesium ribbons are taken in test tubes A and B. HCl is added to A and acetic acid to B. In which test tube will the fizzing occur more vigorously? Test tube A. HCl is a strong acid and produces more H+ ions than acetic acid. Higher H+ ion concentration causes more vigorous reaction with magnesium, producing more hydrogen gas faster.

Acid Bases and Salts Class 10 Questions and Answers: pH Scale and Importance of pH

pH questions carry 1-2 marks and appear in almost every CBSE 2026 board paper. These acid bases and salts class 10 questions and answers on pH cover every format tested.

Q1. What does the p in pH stand for? The p stands for 'potenz', a German word meaning power. pH measures the power of hydrogen ion concentration in a solution.

Q2. What is the pH of a neutral solution? The pH of a neutral solution is exactly 7. Values below 7 are acidic and values above 7 are basic.

Q3. Five solutions A, B, C, D and E showed pH as 4, 1, 11, 7 and 9 respectively. Which solution is neutral, strongly alkaline, strongly acidic, weakly acidic, and weakly alkaline? Neutral: D (pH 7). Strongly alkaline: C (pH 11). Strongly acidic: B (pH 1). Weakly acidic: A (pH 4). Weakly alkaline: E (pH 9).

Q4. What is the pH range of acid rain? Acid rain has a pH less than 5.6. Normal rain has a pH of about 5.6 due to dissolved CO2 forming carbonic acid.

Q5. Why does tooth decay start when pH in the mouth falls below 5.5? Tooth enamel is made of calcium phosphate. It dissolves when the pH in the mouth falls below 5.5. Bacteria produce acids from food particles, lowering the pH and corroding the enamel.

Q6. Fresh milk has a pH of 6. How does the pH change as it turns into curd? The pH decreases. Bacteria convert lactose into lactic acid when milk changes to curd. The increase in acid lowers the pH below 6.

Q7. What is the pH range within which the human body works? The human body works within the pH range of 7.0 to 7.8. Living organisms can survive only within a narrow pH range.

Q8. A milkman adds a very small amount of baking soda to fresh milk. Why does the pH shift to slightly alkaline? Why does this milk take a long time to set as curd? Baking soda (NaHCO3) is basic and raises the pH of milk to slightly above 7. Lactic acid produced by bacteria first neutralises the added base before the pH can drop enough for curd to set. This slows down curd formation.

Q9. Under what soil condition would a farmer use quicklime or slaked lime? A farmer uses quicklime (CaO) or slaked lime (Ca(OH)2) when soil is too acidic. These basic substances neutralise excess acid in the soil.

Q10. Do basic solutions also have H+ ions? If yes, why are they basic? Yes. Both acidic and basic solutions contain H+ and OH- ions. A solution is basic when the concentration of OH- ions is greater than the concentration of H+ ions.

Salts and Their Families: Short Answer Questions

These class 10 science chapter 2 important questions on salts and common salt products are high-priority for CBSE 2026 board exams.

Q1. What is the pH of a salt formed from a strong acid and a strong base? The pH is 7. Such salts are neutral. Example: NaCl formed from HCl and NaOH.

Q2. Name the salt used for softening hard water. Sodium carbonate (washing soda) is used to soften hard water. It removes permanent hardness.

Q3. What is the common name of Ca(ClO)2? Bleaching powder.

Q4. Name the substance that on treatment with chlorine gives bleaching powder. Slaked lime (calcium hydroxide, Ca(OH)2). The reaction is: 2Ca(OH)2 + 2Cl2 → Ca(ClO)2 + CaCl2 + 2H2O.

Q5. What happens when crystals of washing soda are exposed to air? Washing soda crystals lose molecules of water of crystallisation to the air. This process is called efflorescence. The crystals become white powder. Na2CO3.10H2O → Na2CO3.H2O + 9H2O.

Q6. Why is sodium hydrogencarbonate an essential ingredient in antacids? NaHCO3 is mildly basic. It neutralises the excess HCl produced in the stomach during indigestion. NaHCO3 + HCl → NaCl + H2O + CO2.

Q7. What is efflorescence? Give an example. Efflorescence is the loss of water of crystallisation from a hydrated salt on exposure to air. Washing soda crystals (Na2CO3.10H2O) turn into white powder (Na2CO3.H2O) on exposure to air.

Q8. Give two important uses of washing soda and baking soda. Washing soda uses: (i) used in glass, soap and paper industries; (ii) removes permanent hardness of water. Baking soda uses: (i) used in baking powder to make bread and cakes soft and spongy; (ii) used as an antacid.

Q9. What is the chemical name of washing soda? Name three raw materials used in making washing soda by the Solvay process. Chemical name: Sodium carbonate decahydrate (Na2CO3.10H2O). Raw materials: ammonia, brine (NaCl solution), and limestone (CaCO3).

Q10. Why does baking soda taste bitter if used instead of baking powder in a cake? On heating, baking soda forms sodium carbonate which has a bitter taste. 2NaHCO3 → Na2CO3 + H2O + CO2. Baking powder contains tartaric acid which neutralises the sodium carbonate, preventing the bitter taste.

Acid Bases and Salts Class 10 Extra Questions: Common Salt, Bleaching Powder, Baking Soda, and Washing Soda

These acid bases and salts class 10 extra questions cover the most important common salt derivatives tested in CBSE 2026 board exams.

Q1. What is the chlor-alkali process? When electricity is passed through an aqueous solution of sodium chloride (brine), it decomposes into sodium hydroxide, chlorine gas, and hydrogen gas. This is called the chlor-alkali process. 2NaCl(aq) + 2H2O(l) → 2NaOH(aq) + Cl2(g) + H2(g).

Q2. Name the products of the chlor-alkali process and state one use of each. Chlorine: used for making bleaching powder and PVC. Hydrogen: used as fuel and for making ammonia. Sodium hydroxide: used for making soaps, detergents, and paper.

Q3. A compound X on electrolysis in an aqueous solution produces a strong base Y, along with two gases A and B. B is used in the manufacture of bleaching powder. Identify X, Y, A, and B. X = NaCl. Y = NaOH. A = H2. B = Cl2. 2NaCl(aq) + 2H2O(l) → 2NaOH(aq) + Cl2(g) + H2(g).

Q4. What is baking powder? What is the role of tartaric acid in baking powder? Baking powder is a mixture of baking soda (NaHCO3) and tartaric acid. When heated or mixed with water, CO2 is released, making bread and cakes soft and spongy. Tartaric acid neutralises the sodium carbonate formed during the reaction, preventing the bitter taste.

Q5. A substance X is used in the kitchen for making crispy pakoras and also as an antacid. Name X, give its chemical formula, and write the reaction when it is heated. X = Baking soda (NaHCO3). 2NaHCO3 → Na2CO3 + H2O + CO2 (on heating).

Q6. Why is bleaching powder not used for bleaching delicate fabrics? Bleaching powder is a strong oxidising agent. It can damage the fibres of delicate fabrics. Mild bleaching agents are preferred for such materials.

Q7. A yellow powder is prepared by the reaction of slaked lime with chlorine. It is used for disinfecting drinking water. Name the yellow powder and write the reaction involved. Bleaching powder (CaOCl2). Ca(OH)2 + Cl2 → CaOCl2 + H2O.

Water of Crystallisation and Plaster of Paris: Questions

Q1. What is water of crystallisation? Water of crystallisation is the fixed number of water molecules present in one formula unit of a salt. Example: CuSO4.5H2O (blue vitriol) has five water molecules.

Q2. A student heated a few crystals of copper sulphate in a dry boiling tube. What change in colour would occur? Where would the water droplets come from? Copper sulphate crystals turn from blue to white on heating. Water droplets appear because the crystals lose their water of crystallisation on heating. The water molecules are released as steam which condenses in the cooler upper part of the tube.

Q3. What is gypsum? How is it different from Plaster of Paris? Gypsum is CaSO4.2H2O. Plaster of Paris is CaSO4.½H2O. Plaster of Paris is made by heating gypsum at 373 K. When mixed with water, Plaster of Paris converts back to gypsum, which causes it to harden. CaSO4.½H2O + 1½H2O → CaSO4.2H2O.

Q4. Why should Plaster of Paris be stored in a moisture-proof container? Plaster of Paris absorbs moisture from the air and converts to gypsum, which is hard. Once this happens, the powder loses its ability to set when mixed with water and becomes useless.

Q5. Blue vitriol changes to white on heating. Why does it turn blue again when water is added? Blue vitriol (CuSO4.5H2O) loses its water of crystallisation on heating, turning white anhydrous copper sulphate (CuSO4). When water is added, the water molecules re-attach to the salt and the blue colour returns.

Important Reactions and Equations for Class 10 Science Chapter 2

Board exams consistently ask students to write and balance equations. These are the most important reactions from acids bases and salts class 10 important questions.

1. Acid + Metal → Salt + Hydrogen gas: Zn + H2SO4 → ZnSO4 + H2. Mg + 2HCl → MgCl2 + H2. 2Al + 3H2SO4 → Al2(SO4)3 + 3H2. Fe + 2HCl → FeCl2 + H2.
2. Acid + Carbonate → Salt + Water + CO2: Na2CO3 + 2HCl → 2NaCl + H2O + CO2. NaHCO3 + HCl → NaCl + H2O + CO2.
3. Acid + Base → Salt + Water (Neutralisation): NaOH + HCl → NaCl + H2O. KOH + HNO3 → KNO3 + H2O.
4. Base + Metal → Salt + Hydrogen gas: 2NaOH + Zn → Na2ZnO2 + H2.
5. Acid + Metal oxide → Salt + Water: CuO + H2SO4 → CuSO4 + H2O.
6. Chlor-alkali process: 2NaCl(aq) + 2H2O(l) → 2NaOH(aq) + Cl2(g) + H2(g).
7. Manufacture of bleaching powder: 2Ca(OH)2 + 2Cl2 → Ca(ClO)2 + CaCl2 + 2H2O.
8. Baking soda on heating: 2NaHCO3 → Na2CO3 + H2O + CO2.
9. Manufacture of baking soda: NaCl + H2O + CO2 + NH3 → NH4Cl + NaHCO3.
10. Plaster of Paris to gypsum: CaSO4.½H2O + 1½H2O → CaSO4.2H2O.
11. Gypsum to Plaster of Paris: CaSO4.2H2O → CaSO4.½H2O + 1½H2O (at 373 K).
12. Lime water and CO2: Ca(OH)2 + CO2 → CaCO3 + H2O (lime water turns milky). CaCO3 + H2O + CO2 → Ca(HCO3)2 (excess CO2, milkiness disappears).

Long Answer Questions from Chapter 2

These acid base and salt important question answers are structured for 5-mark CBSE 2026 board responses.

Q1. What happens when sodium chloride solution is electrolysed? Name all products and give two uses of each. When electricity is passed through aqueous sodium chloride (brine), the chlor-alkali process occurs. 2NaCl(aq) + 2H2O(l) → 2NaOH(aq) + Cl2(g) + H2(g).

Chlorine gas forms at the anode. Hydrogen gas forms at the cathode. Sodium hydroxide forms near the cathode.

Uses of Cl2: (i) making bleaching powder; (ii) disinfecting water. Uses of H2: (i) as fuel; (ii) making ammonia for fertilisers. Uses of NaOH: (i) making soap and detergents; (ii) paper manufacturing.

Q2. Give the preparation, chemical name, formula, and uses of baking soda, washing soda, and bleaching powder.

Baking soda: Chemical name: Sodium hydrogencarbonate. Formula: NaHCO3. Prepared using NaCl, H2O, CO2, NH3. Uses: baking powder, antacid, soda-acid fire extinguisher.

Washing soda: Chemical name: Sodium carbonate decahydrate. Formula: Na2CO3.10H2O. Prepared by recrystallising Na2CO3 obtained from heated NaHCO3. Uses: softening hard water, glass and paper industries, cleaning agent.

Bleaching powder: Formula: Ca(ClO)2. Prepared by treating slaked lime with chlorine. Uses: bleaching textiles and wood pulp, disinfecting drinking water, oxidising agent in industries.

Q3. Explain the importance of pH in everyday life with four examples.

In digestion: The stomach produces HCl (pH 1-2). During indigestion, excess acid causes pain. Antacids (basic substances) neutralise this acid.

In tooth decay: Tooth enamel corrodes when mouth pH falls below 5.5. Toothpaste (basic) neutralises the acid produced by bacteria.

In plants: Plants grow best in a specific pH range. Acidic soil is treated with lime. Alkaline soil is treated with organic material.

In bee sting and ant sting: Bee sting is acidic and baking soda (basic) applied gives relief. Ant sting releases methanoic acid and a mild base neutralises the pain.