NCERT Solutions Class 10 Science Chapter 2 – Acids, Bases and Salts
Complete NCERT Solutions for Class 10 Science Chapter 2 – Acids, Bases and Salts. This chapter covers properties of acids and bases, pH scale, salts, and their chemical reactions with detailed explanations.
Chapter Overview
| Topic | Weightage |
|---|---|
| Properties of Acids and Bases | 3-4 marks |
| Chemical Reactions | 3-4 marks |
| pH Scale and Indicators | 2-3 marks |
| Salts and their Properties | 3-4 marks |
| Total Chapter Weightage | 8-10 marks |
Key Concepts
1. Acids
- Definition: Substances that produce H⁺ ions in water
- Properties: Sour taste, turn blue litmus red, conduct electricity
- Examples: HCl, H₂SO₄, HNO₃, CH₃COOH
2. Bases
- Definition: Substances that produce OH⁻ ions in water
- Properties: Bitter taste, soapy feel, turn red litmus blue
- Examples: NaOH, KOH, Ca(OH)₂, NH₄OH
3. pH Scale
- Ranges from 0 to 14
- pH < 7: Acidic
- pH = 7: Neutral
- pH > 7: Basic/Alkaline
Important Chemical Reactions
Acid + Metal → Salt + Hydrogen
2HCl + Zn → ZnCl₂ + H₂↑
H₂SO₄ + Fe → FeSO₄ + H₂↑
Acid + Metal Carbonate → Salt + CO₂ + Water
2HCl + Na₂CO₃ → 2NaCl + H₂O + CO₂↑
2HCl + CaCO₃ → CaCl₂ + H₂O + CO₂↑
Acid + Base → Salt + Water (Neutralization)
HCl + NaOH → NaCl + H₂O
H₂SO₄ + 2NaOH → Na₂SO₄ + 2H₂O
Acid + Metal Oxide → Salt + Water
2HCl + CuO → CuCl₂ + H₂O
NCERT Exercise Solutions
Question 1
You have been provided with three test tubes. One of them contains distilled water and the other two contain an acidic solution and a basic solution, respectively. If you are given only red litmus paper, how will you identify the contents of each test tube?
Step 1: Put red litmus paper in all three test tubes.
Step 2: The solution that turns red litmus to blue is the basic solution.
Step 3: Now dip the blue litmus (from step 2) in the remaining two solutions.
Step 4: The solution that turns blue litmus to red is the acidic solution.
Step 5: The remaining solution that shows no change is distilled water.
Question 2
Why should curd and sour substances not be kept in brass and copper vessels?
Curd and sour substances contain acids. These acids react with brass and copper metals to form toxic compounds (salts of copper) which are harmful for health. The reaction is:
Cu + 2CH₃COOH → Cu(CH₃COO)₂ + H₂↑
The copper acetate formed is poisonous.
Question 3
Which gas is usually liberated when an acid reacts with a metal? Illustrate with an example. How will you test for the presence of this gas?
Gas liberated: Hydrogen gas (H₂)
Example: Zn + H₂SO₄ → ZnSO₄ + H₂↑
Test: Bring a burning matchstick near the gas. Hydrogen burns with a pop sound (characteristic test for H₂).
Question 4
Metal compound A reacts with dilute hydrochloric acid to produce effervescence. The gas evolved extinguishes a burning candle. Write a balanced chemical equation for the reaction if one of the compounds formed is calcium chloride.
The gas that extinguishes a burning candle is CO₂.
Since calcium chloride is formed, the metal compound A is calcium carbonate (CaCO₃).
Balanced equation:
CaCO₃ + 2HCl → CaCl₂ + H₂O + CO₂↑
Question 5
Why do HCl, HNO₃, etc., show acidic characters in aqueous solutions while solutions of compounds like alcohol and glucose do not show acidic character?
HCl, HNO₃, etc., dissociate in water to produce hydrogen ions (H⁺):
HCl → H⁺ + Cl⁻
These H⁺ ions are responsible for acidic character.
Alcohol and glucose, though containing hydrogen, do not dissociate in water to produce H⁺ ions. Hence, they do not show acidic character.
Important Salts
Common Salt (NaCl)
- Source: Sea water, rock salt deposits
- Uses: Cooking, preservation, chemical industry
- Chemicals made: NaOH, Cl₂, Na₂CO₃, NaHCO₃
Baking Soda (NaHCO₃)
- Preparation: NaCl + H₂O + CO₂ + NH₃ → NH₄Cl + NaHCO₃
- Uses: Baking, antacid, fire extinguisher
Washing Soda (Na₂CO₃.10H₂O)
- Preparation: 2NaHCO₃ → Na₂CO₃ + H₂O + CO₂
- Uses: Cleaning, water softening, glass making
Plaster of Paris (CaSO₄.½H₂O)
- Preparation: CaSO₄.2H₂O → CaSO₄.½H₂O + 1½H₂O
- Uses: Plaster casts, statues, decoration
Important Points for Exam
- Acids turn blue litmus red; bases turn red litmus blue
- Universal indicator shows different colors for different pH values
- Our stomach contains HCl (gastric juice)
- Antacids neutralize excess stomach acid
- Tooth decay starts when mouth pH falls below 5.5
- Bees inject formic acid; wasps inject alkaline liquid
Leave a Reply