Introduction
Acids, Bases and Salts is an important chapter of Class 10 Chemistry that explains the properties, theories, reactions, and applications of acids, bases, and salts. The chapter introduces the Arrhenius, Brønsted–Lowry, and Lewis concepts of acids and bases and explains how these substances behave in aqueous solutions.
Students also learn about the pH scale, indicators, neutralization reactions, strong and weak acids and bases, amphoteric substances, preparation and classification of salts, and the uses of common salts such as sodium chloride, baking soda, and washing soda. These concepts have important applications in industry, agriculture, medicine, household products, and environmental chemistry.
These Class 10 Chemistry Chapter 2 MCQs are prepared according to the Punjab and Sindh Board syllabus to help students revise important concepts, strengthen their understanding, and prepare confidently for board examinations.
Learning Outcomes
After studying this chapter, students will be able to:
- Define acids, bases, and salts.
- Explain the Arrhenius concept of acids and bases.
- Explain the Brønsted–Lowry concept of acids and bases.
- Describe the Lewis concept of acids and bases.
- Differentiate between strong and weak acids and bases.
- Explain the pH scale.
- Identify acidic, basic, and neutral solutions using pH values.
- Describe the action of common acid-base indicators.
- Explain neutralization reactions.
- Define amphoteric substances.
- Explain the preparation and classification of salts.
- Identify common salts and their uses.
- Explain important reactions of acids with metals and carbonates.
- Describe industrial applications of acids, bases, and salts.
Quick Notes – Chapter Summary
- Acids increase the concentration of H⁺ ions in aqueous solutions according to the Arrhenius concept.
- Bases increase the concentration of OH⁻ ions in aqueous solutions according to the Arrhenius concept.
- A Brønsted–Lowry acid donates a proton (H⁺), while a Brønsted–Lowry base accepts a proton.
- A Lewis acid accepts an electron pair, while a Lewis base donates an electron pair.
- Acids turn blue litmus red.
- Bases turn red litmus blue.
- The pH scale generally ranges from 0 to 14.
- A solution with pH less than 7 is acidic.
- A solution with pH 7 is neutral at 25°C.
- A solution with pH greater than 7 is basic/alkaline.
- Strong acids and bases ionize almost completely in aqueous solutions.
- Weak acids and bases ionize only partially.
- Neutralization occurs when an acid reacts with a base to form salt and water.
- Phenolphthalein is colourless in acidic solution and pink in basic solution.
- Methyl orange is red in acidic solution and yellow in alkaline solution.
- Amphoteric substances can act as both acids and bases.
- Aluminium hydroxide (Al(OH)₃) is an example of an amphoteric substance.
- Acids react with many metals to produce salt and hydrogen gas.
- Acids react with metal carbonates to produce salt, water, and carbon dioxide.
- Common salts include sodium chloride, sodium hydrogen carbonate, and sodium carbonate.
- Baking soda is sodium hydrogen carbonate (NaHCO₃).
- Washing soda is sodium carbonate decahydrate (Na₂CO₃·10H₂O).
- Sulfuric acid is manufactured industrially by the Contact process.
- Sodium hydroxide is widely used in industries such as paper, soap, and textiles.
Important Definitions
Acid: A substance that produces H⁺ ions in aqueous solution according to the Arrhenius concept.
Base: A substance that produces OH⁻ ions in aqueous solution according to the Arrhenius concept.
Arrhenius Acid: A substance that increases the concentration of H⁺ ions in aqueous solution.
Arrhenius Base: A substance that increases the concentration of OH⁻ ions in aqueous solution.
Brønsted–Lowry Acid: A substance that donates a proton (H⁺).
Brønsted–Lowry Base: A substance that accepts a proton (H⁺).
Lewis Acid: A substance that accepts an electron pair.
Lewis Base: A substance that donates an electron pair.
pH: A measure of the acidity or basicity of an aqueous solution.
Neutralization: A reaction between an acid and a base that generally produces salt and water.
Indicator: A substance that changes colour depending on whether a solution is acidic or basic.
Strong Acid: An acid that ionizes almost completely in aqueous solution.
Weak Acid: An acid that ionizes only partially in aqueous solution.
Amphoteric Substance: A substance that can behave as both an acid and a base.
Salt: An ionic compound generally formed when the hydrogen ions of an acid are replaced by metal ions or ammonium ions.
Important Concepts
- Arrhenius theory
- Brønsted–Lowry theory
- Lewis theory
- Strong and weak acids
- Strong and weak bases
- pH scale
- Acid-base indicators
- Neutralization reactions
- Amphoteric substances
- Reactions of acids with metals
- Reactions of acids with metal carbonates
- Preparation of salts
- Classification of salts
- Common salts and their uses
- Sodium chloride
- Sodium hydrogen carbonate
- Sodium carbonate
- Industrial uses of acids and bases
- Contact process
Class 10 Chemistry Chapter 2 – Acids, Bases and Salts MCQs
1. According to Arrhenius theory, an acid is a substance that:
- A. Increases the concentration of OH⁻ ions in solution
- B. Increases the concentration of H⁺ ions in solution ✅
- C. Donates an electron pair
- D. Accepts an electron pair
Explanation: Arrhenius defined acids as substances that release hydrogen ions (H⁺) in aqueous solution.
2. Which of the following is a Brønsted–Lowry base?
- A. HCl
- B. H₂SO₄
- C. NH₃ ✅
- D. CO₂
Explanation: In the Brønsted–Lowry concept, a base is a proton (H⁺) acceptor; ammonia accepts a proton to form NH₄⁺.
3. In Lewis theory, a base is defined as:
- A. Proton donor
- B. Electron pair donor ✅
- C. Electron pair acceptor
- D. Hydrogen ion donor
Explanation: Lewis bases donate an electron pair to form a coordinate covalent bond.
4. Which of the following is a strong acid?
- A. CH₃COOH
- B. H₂CO₃
- C. HNO₃ ✅
- D. NH₄OH
Explanation: Nitric acid (HNO₃) completely ionizes in aqueous solution, making it a strong acid.
5. A solution has a pH of 3. It is:
- A. Acidic ✅
- B. Neutral
- C. Basic
- D. Amphoteric
Explanation: pH values less than 7 indicate acidic solutions.
6. Which of the following is NOT an example of a base?
- A. NaOH
- B. KOH
- C. H₂SO₄ ✅
- D. Ca(OH)₂
Explanation: H₂SO₄ is sulfuric acid, not a base.
7. Neutralization is a reaction between:
- A. An acid and a base ✅
- B. Two acids
- C. Two bases
- D. A salt and water
Explanation: Neutralization occurs when H⁺ ions from acids combine with OH⁻ ions from bases to form water and a salt.
8. Which indicator turns pink in basic solutions?
- A. Methyl orange
- B. Phenolphthalein ✅
- C. Litmus (blue form)
- D. Bromothymol blue
Explanation: Phenolphthalein is colourless in acidic solutions and turns pink in basic solutions.
9. Common salt (NaCl) is obtained by:
- A. Direct combination of Na and Cl₂ gas
- B. Neutralization of HCl with NaOH ✅
- C. Reaction of Na₂CO₃ with water
- D. Electrolysis of brine only
Explanation: Industrially, NaCl can be obtained from brine, but in the lab, it is prepared by neutralizing hydrochloric acid with sodium hydroxide.
10. Which of the following is an amphoteric substance?
- A. H₂SO₄
- B. NaOH
- C. Al(OH)₃ ✅
- D. HNO₃
Explanation: Amphoteric substances act as both acids and bases depending on the reacting partner.
11. The pH of pure water at 25°C is:
- A. 6
- B. 7 ✅
- C. 8
- D. 10
Explanation: Pure water is neutral, with equal H⁺ and OH⁻ concentrations, giving pH = 7 at 25°C.
12. Baking soda is chemically known as:
- A. Sodium carbonate
- B. Sodium hydrogen carbonate ✅
- C. Calcium carbonate
- D. Potassium carbonate
Explanation: Baking soda is NaHCO₃, used in cooking and as an antacid.
13. Which salt is used in the manufacture of soap and glass?
- A. NaCl
- B. Na₂CO₃ ✅
- C. KNO₃
- D. CaSO₄·2H₂O
Explanation: Sodium carbonate (washing soda) is used in glass manufacturing and water softening.
14. Which acid is present in vinegar?
- A. Citric acid
- B. Acetic acid ✅
- C. Formic acid
- D. Lactic acid
Explanation: Vinegar is a dilute aqueous solution of acetic acid (CH₃COOH).
15. Which base is used in the manufacture of paper?
- A. Na₂CO₃
- B. NaOH ✅
- C. Ca(OH)₂
- D. NH₄OH
Explanation: Sodium hydroxide is used in the pulp and paper industry for processing wood chips into paper.
16. Which of the following salts results from a weak acid and a strong base?
- A. NaCl
- B. Na₂CO₃ ✅
- C. KCl
- D. NH₄Cl
Explanation: Sodium carbonate comes from the neutralization of carbonic acid (weak) with sodium hydroxide (strong).
17. Which gas is released when an acid reacts with a metal carbonate?
- A. Oxygen
- B. Hydrogen
- C. Carbon dioxide ✅
- D. Nitrogen
Explanation: Acid + metal carbonate → salt + water + carbon dioxide gas.
18. Which industrial process is used to produce sulfuric acid?
- A. Haber process
- B. Solvay process
- C. Contact process ✅
- D. Ostwald process
Explanation: Sulfuric acid is manufactured by the Contact process involving catalytic oxidation of SO₂ to SO₃.
19. Which indicator is red in an acidic solution and yellow in a basic solution?
- A. Methyl orange ✅
- B. Phenolphthalein
- C. Blue litmus
- D. Starch
Explanation: Methyl orange is red in acidic solutions and changes to yellow in alkaline solutions.
20. Which gas is produced when an acid reacts with an active metal?
- A. Oxygen
- B. Hydrogen ✅
- C. Carbon dioxide
- D. Nitrogen
Explanation: Acids react with many active metals to produce a salt and hydrogen gas.
21. Which of the following is a weak acid?
- A. HCl
- B. HNO₃
- C. CH₃COOH ✅
- D. H₂SO₄
Explanation: Acetic acid (CH₃COOH) is a weak acid because it ionizes only partially in water.
22. A solution with a pH of 10 is:
- A. Strongly acidic
- B. Neutral
- C. Basic ✅
- D. Amphoteric
Explanation: Solutions with pH values greater than 7 are basic or alkaline.
Exam Tips
- Memorize the definitions of Arrhenius, Brønsted–Lowry, and Lewis acids and bases.
- Remember the difference between a strong acid and a weak acid.
- Learn the important pH values and what they indicate.
- Memorize the colour changes of litmus, methyl orange, and phenolphthalein.
- Practice equations for neutralization reactions.
- Remember:
- Acid + Base → Salt + Water
- Acid + Metal → Salt + Hydrogen
- Acid + Carbonate → Salt + Water + Carbon dioxide
- Learn the formulas and uses of NaCl, NaHCO₃, and Na₂CO₃·10H₂O.
- Understand the meaning of amphoteric substances.
- Remember that pH < 7 is acidic, pH = 7 is neutral, and pH > 7 is basic at 25°C.
- Study the Contact process for the industrial manufacture of sulfuric acid.
- Learn the major industrial uses of NaOH and Na₂CO₃.
Common Mistakes
❌ Confusing Arrhenius, Brønsted–Lowry, and Lewis definitions.
❌ Thinking that all bases must contain OH⁻. This is not true under the Brønsted–Lowry or Lewis concepts.
❌ Confusing strong acids with concentrated acids.
❌ Forgetting that pH decreases as acidity increases.
❌ Mixing up the colour changes of phenolphthalein and methyl orange.
❌ Confusing baking soda (NaHCO₃) with washing soda (Na₂CO₃·10H₂O).
❌ Forgetting that acid-carbonate reactions release CO₂.
❌ Confusing an amphoteric substance with a neutral substance.
❌ Assuming that neutralization always means the final solution has exactly pH 7. The pH of the resulting solution can depend on the strengths of the acid and base involved.
Conclusion
Acids, Bases and Salts is an important chapter for understanding many chemical reactions that occur in laboratories, industries, living organisms, and everyday life. The concepts of acid-base theories, pH, indicators, neutralization, amphoteric substances, and salts provide a strong foundation for further study of chemistry.
Understanding common substances such as hydrochloric acid, sulfuric acid, sodium hydroxide, sodium chloride, baking soda, and washing soda, along with their properties and uses, helps students connect chemistry with practical applications.
Regular practice of these MCQs will strengthen conceptual understanding and help students prepare effectively for Class 10 Chemistry board examinations.