Extra 20 long-answer questions for Chapter:2 Acids, Bases, and Salts from Class 10 CBSE Science.
Chapter 2, "Acids, Bases, and Salts," is a foundational chapter in the Chemistry section that introduces students to the fundamental concepts of these three important classes of chemical compounds. This chapter not only explains the theoretical aspects of acids, bases, and salts but also highlights their significance in our daily lives and in industrial applications.
Weightage in the Board Exam (Approximate)
"Acids, Bases, and Salts" falls under Unit I: Chemical Substances – Nature and Behaviour, which collectively carries a significant weightage of 25 marks in the 80-mark theory paper.
Based on past trends and common weightage distribution, Chapter 2 generally carries an individual weightage of 3 to 6 marks.
1. Define acids and bases. Explain their physical and chemical properties with examples.
Answer:
Acids: Substances that release H⁺ ions in solution. Example: HCl, H₂SO₄.
Bases: Substances that release OH⁻ ions in solution. Example: NaOH, Ca(OH)₂.
Physical Properties of Acids:
Sour taste
Turns blue litmus red
Conducts electricity in aqueous solution
Physical Properties of Bases:
4. Bitter taste
5. Turns red litmus blue
6. Feels slippery
Chemical Properties:
7. Acids react with metals to form H₂ gas
8. Bases react with acids to form salt and water (Neutralization reaction)
2. What are indicators? Explain different types with examples and their uses.
Answer:
Indicators: Substances that change colour based on pH.
Types of Indicators:
Natural Indicators: Litmus (Acid: red, Base: blue)
Synthetic Indicators: Methyl orange (Acid: red, Base: yellow)
Olfactory Indicators: Onion, vanilla (Smell changes in bases)
Universal Indicator: Measures exact pH using color changes.
Uses:
5. Testing pH in laboratories.
6. Checking soil acidity for farming.
7. Monitoring acid rain impact.
3. What is the pH scale? How does pH affect daily life?
Answer:
pH scale measures acidity/basicity (0-14).
Acidic (pH < 7), Neutral (pH = 7), Basic (pH > 7).
Daily Life Applications:
Stomach acid (pH 1.5-3.5) helps digestion.
Tooth decay (pH < 5.5) causes enamel erosion.
Soil pH affects plant growth.
Acid rain (pH < 5.6) damages buildings and crops.
Aquatic life requires neutral water pH.
Antacids (pH > 7) neutralize excess stomach acid.
4. What happens when acids react with metals, metal oxides, and carbonates? Give examples.
Answer:
Acid + Metal → Salt + Hydrogen gas
Example: Zn+2HCl→ZnCl2+H2↑
Acid + Metal Oxide → Salt + Water
Example: CuO+H2SO4→CuSO4+H2O
Acid + Metal Carbonate → Salt + CO₂ + Water
Example: Na2CO3+2HCl→2NaCl+CO2+H2O
Hydrogen gas test: Burning matchstick produces a pop sound.
CO₂ gas test: Turns lime water milky.
5. Explain neutralization reactions with examples and applications.
Answer:
Definition: Acid + Base → Salt + Water
Examples:
HCl + NaOH → NaCl + H₂O
H₂SO₄ + Ca(OH)₂ → CaSO₄ + 2H₂O
Applications:
3. Antacids neutralize stomach acid.
4. Lime (Ca(OH)₂) is used in soil to reduce acidity.
5. Factory waste is neutralized before disposal.
6. Explain the preparation of common salt (NaCl) and its uses.
Answer:
Seawater evaporation leaves behind salt.
Purification removes impurities.
Uses:
Food seasoning.
Preservative.
Making caustic soda.
7. What is bleaching powder? How is it prepared? Give its uses.
Answer:
Formula: CaOCl₂
Preparation: Ca(OH)2+Cl2→CaOCl2+H2O
Uses:
Water purification.
Bleaching fabrics.
8. What is baking soda? How is it prepared? Write its uses.
Answer:
Formula: NaHCO₃
Uses:
Baking.
Fire extinguishers.
9. What is washing soda? Write its uses.
Answer:
Formula: Na₂CO₃·10H₂O
Uses:
Glass manufacturing.
Softening water.
10. What is Plaster of Paris? How is it prepared? Write its uses.
Answer:
Formula: CaSO₄·½H₂O
Uses:
Medical bandages.
Making statues.
11. Explain how antacids work with the help of equations.
Answer:
Antacids are substances that neutralize excess stomach acid (HCl) and provide relief from acidity and heartburn.
Examples of antacids:
Magnesium hydroxide (Milk of Magnesia)
Aluminium hydroxide
Sodium bicarbonate (Baking soda)
Chemical Equations:
Magnesium hydroxide reaction: Mg(OH)2+2HCl→MgCl2+2H2O
Sodium bicarbonate reaction: NaHCO3+HCl→NaCl+CO2+H2O
Uses of Antacids:
Used in medicines for acid reflux and indigestion.
Provides relief from ulcers and gastritis.
Used in first-aid treatments for acid burns.
12. Why is water pH important for aquatic life?
Answer:
Water pH affects the survival of fish, plants, and microorganisms in water bodies.
Ideal pH for aquatic life: 6.5 to 8.5
Effects of low pH (Acidic water):
Kills fish and aquatic plants.
Dissolves toxic metals from rocks and pipes, contaminating water.
Leads to acid rain, which lowers the pH of lakes and rivers.
Effects of high pH (Basic water):
4. Reduces oxygen solubility, suffocating fish.
5. Promotes excessive algae growth (Eutrophication).
6. Hardens fish scales and damages gills.
13. How do bases react with ammonium salts? Give an example.
Answer: Reaction of Bases with Ammonium Salts
When a base reacts with an ammonium salt, it produces ammonia gas (NH₃), along with water and a salt.
This is an example of a neutralization reaction, where the base removes H⁺ ions from the ammonium salt, releasing ammonia gas.
Example: Reaction of Ammonium Chloride (NH₄Cl) with Sodium Hydroxide (NaOH)
NH4Cl+NaOH→NaCl+NH3↑+H2O
14. Why are food packets filled with nitrogen instead of oxygen?
Answer:
Oxygen causes food to spoil due to oxidation and bacterial growth.
Nitrogen is used because:
It is an inert gas – does not react with food.
Prevents the growth of bacteria and fungi.
Keeps chips and snacks fresh for a longer time.
Prevents rancidity of oils and fats.
Maintains crispness of packaged food.
15. Why does milk turn sour over time? What chemical change occurs?
Answer:
Milk contains lactose (a type of sugar).
When left open, lactic acid bacteria (Lactobacillus) convert lactose into lactic acid.
Chemical reaction: C12H22O11+H2O→4C3H6O3
Effects:
Increase in acidity (Lower pH).
Coagulation of proteins (Milk curdles).
Formation of curd (Fermented milk).
Prevention:
Refrigeration slows bacterial growth.
Pasteurization kills bacteria.
16. What is the role of pH in agriculture?
Answer:
Soil pH affects plant growth and nutrient absorption.
Optimal soil pH: 6-7.5
Acidic Soil (pH < 6):
Deficiency of calcium and magnesium.
Solution: Add slaked lime (Ca(OH)₂) or quicklime (CaO).
Alkaline Soil (pH > 7.5):
3. Poor absorption of iron, zinc, phosphorus.
4. Solution: Add organic matter like manure or sulphur.
Farmers use pH meters to test soil acidity and apply fertilizers accordingly.
17. Explain the effect of acid rain on monuments like the Taj Mahal.
Answer:
Acid rain contains sulfuric acid (H₂SO₄) and nitric acid (HNO₃).
Reaction with Marble (CaCO₃): CaCO3+H2SO4→CaSO4+CO2+H2O
Effects on Taj Mahal:
Marble loses its shine (Marble cancer).
Formation of yellowish patches.
Erosion of carved designs.
Weakens structural strength.
Prevention Measures:
5. Restrict industrial pollution near monuments.
6. Use cleaner fuels to reduce emissions.
7. Regular cleaning and maintenance of heritage sites.
18. How does acid rain affect aquatic life and soil?
Answer:
Acid rain contains sulfuric and nitric acid from pollution.
Effects on Aquatic Life:
Lowers water pH, making it toxic.
Kills fish and amphibians.
Dissolves heavy metals like lead into water.
Effects on Soil:
4. Reduces fertility by removing nutrients.
5. Kills useful soil bacteria.
6. Increases soil erosion.
19. Why does tamarind taste sour? Explain the chemical reason.
Answer:
Tamarind contains tartaric acid (C₄H₆O₆), which is responsible for its sour taste.
Acidic substances taste sour due to H⁺ ions.
Other natural acids:
Citric acid – Lemons, oranges.
Acetic acid – Vinegar.
Lactic acid – Curd.
20. Why do acids conduct electricity while solid salt does not?
Answer:
Acids release free H⁺ ions in aqueous solution, allowing current flow.
Solid salt (NaCl) does not conduct electricity because:
No free ions in solid form.
When dissolved in water, Na⁺ and Cl⁻ become free, making it conductive.
Example:
HCl in water: Conducts electricity.
Glucose in water: Does not conduct (No ions).
