Acids, bases, and salts are fundamental chemical substances that play a vital role in our daily lives and in various industries. This chapter explains the definitions and properties of acids and bases, different scientific theories such as Arrhenius, Brønsted–Lowry, and Lewis concepts, and the pH scale. It also covers indicators, neutralization reactions, preparation and classification of salts, and their common uses. Students will also learn about the role of acids and bases in industry, health, and the environment.
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.