Class 10 Science Chapter 2 Acids Bases and Salts Solutions
Short Intro
This article provides complete NCERT solutions for Class 10 Science Chapter 2 “Acids, Bases and Salts”. All questions are explained with step-by-step solutions, important concepts, formulas, exam tips, common mistakes, MCQs, and FAQs for better understanding and exam preparation.
Quick Information Box
| Particular | Details |
|---|---|
| Class | 10 |
| Subject | Science |
| Chapter | 2 |
| Chapter Name | Acids, Bases and Salts |
| Board | CBSE / State Boards |
| Important Topics | Acids, Bases, Salts, pH Scale, Neutralisation |
Concepts Used (Topics Covered)
- Properties of Acids and Bases
- Indicators
- Reactions of Acids with Metals
- Reactions with Metal Carbonates
- Neutralisation Reactions
- pH Scale
- Strength of Acids and Bases
- Common Salt and Its Products
- Baking Soda
- Washing Soda
- Bleaching Powder
- Plaster of Paris
- Water of Crystallisation
Important Formulas
- Acid + Metal → Salt + H₂↑
- Acid + Base → Salt + Water
- Acid + Metal Carbonate → Salt + CO₂ + Water
- HCl + NaOH → NaCl + H₂O
- Zn + H₂SO₄ → ZnSO₄ + H₂
- CaCO₃ + 2HCl → CaCl₂ + CO₂ + H₂O
- 2NaHCO₃ → Na₂CO₃ + H₂O + CO₂
NCERT Exercise Solutions
Question 1
A solution turns red litmus blue. Its pH is likely to be?
Solution
Red litmus turning blue indicates a base.
pH of bases is greater than 7.
Among the options, 10 is greater than 7.
Answer
(d) 10
Question 2
A solution reacts with crushed egg-shells and gives a gas that turns lime water milky.
Solution
Egg-shells contain calcium carbonate.
Acids react with carbonates to produce CO₂.
CO₂ turns lime water milky.
Answer
(b) HCl
Question 3
10 mL NaOH is neutralised by 8 mL HCl. How much HCl is needed for 20 mL NaOH?
Solution
20 mL is double of 10 mL.
Required HCl will also double.
8 × 2 = 16 mL
Answer
(d) 16 mL
Question 4
Which medicine is used for indigestion?
Solution
Indigestion is caused by excess acid in the stomach.
Antacids neutralise excess acid.
Answer
(c) Antacid
Question 5
Write balanced equations.
(a)
Zinc + Dilute Sulphuric Acid
Zn + H₂SO₄ → ZnSO₄ + H₂↑
(b)
Magnesium + Hydrochloric Acid
Mg + 2HCl → MgCl₂ + H₂↑
(c)
Aluminium + Sulphuric Acid
2Al + 3H₂SO₄ → Al₂(SO₄)₃ + 3H₂↑
(d)
Iron + Hydrochloric Acid
Fe + 2HCl → FeCl₂ + H₂↑
Question 6
Alcohol and glucose contain hydrogen but are not acids. Prove it.
Solution
Prepare solutions of HCl, glucose and alcohol.
Test electrical conductivity.
HCl solution conducts electricity because it releases H⁺ ions.
Glucose and alcohol do not conduct electricity.
Therefore, they do not release H⁺ ions.
Hence they are not acids.
Question 7
Why does distilled water not conduct electricity but rain water does?
Solution
Distilled water contains almost no ions.
Rain water contains dissolved salts and gases that produce ions.
Therefore rain water conducts electricity.
Question 8
Why does dry HCl gas not show acidic behaviour?
Solution
Acidity is due to H⁺ ions.
Dry HCl gas does not produce H⁺ ions without water.
Hence it does not show acidic behaviour.
Question 9
pH values:
A = 4
B = 1
C = 11
D = 7
E = 9
Answers
(a) Neutral → D
(b) Strongly alkaline → C
(c) Strongly acidic → B
(d) Weakly acidic → A
(e) Weakly alkaline → E
Increasing order of hydrogen ion concentration:
C < E < D < A < B
Question 10
Solution
Fizzing will occur more vigorously in Test Tube A.
Reason:
HCl is a strong acid and produces more H⁺ ions than acetic acid.
Hence magnesium reacts faster with HCl.
Question 11
Solution
Fresh milk has pH 6.
When milk changes into curd, lactic acid is formed.
Therefore pH decreases and becomes more acidic.
Question 12
(a)
Why add baking soda?
Baking soda makes milk slightly alkaline and delays spoilage.
(b)
Why does curd take longer to set?
The alkaline medium neutralises the acid produced by bacteria.
Hence curd formation slows down.
Question 13
Solution
Plaster of Paris absorbs moisture and converts into gypsum.
CaSO₄·½H₂O + 1½H₂O → CaSO₄·2H₂O
Therefore it should be stored in moisture-proof containers.
Question 14
Solution
A reaction between an acid and a base producing salt and water is called neutralisation.
Examples:
- HCl + NaOH → NaCl + H₂O
- H₂SO₄ + 2KOH → K₂SO₄ + 2H₂O
Question 15
Uses of Washing Soda
- Removing permanent hardness of water.
- Used in glass, soap and paper industries.
Uses of Baking Soda
- Making baking powder.
- Used as antacid.
Common Mistakes
- Confusing strong acids with concentrated acids.
- Writing unbalanced chemical equations.
- Assuming all hydrogen-containing compounds are acids.
- Forgetting that pH 7 is neutral.
- Mixing water into concentrated acid instead of acid into water.
Exam Tips
- Learn all important chemical equations.
- Memorize uses of bleaching powder, baking soda and washing soda.
- Remember pH scale values.
- Practice balancing reactions regularly.
- Revise common salts and their formulas.
Practice MCQs
1. Which gas is evolved when zinc reacts with dilute HCl?
A. Oxygen
B. Hydrogen
C. Carbon dioxide
D. Nitrogen
Answer: B
2. pH of a neutral solution is:
A. 0
B. 5
C. 7
D. 14
Answer: C
3. Baking soda formula is:
A. Na₂CO₃
B. NaOH
C. NaHCO₃
D. HCl
Answer: C
4. Which acid is present in vinegar?
A. Citric Acid
B. Acetic Acid
C. Oxalic Acid
D. Lactic Acid
Answer: B
5. Which compound is used in whitewashing?
A. CaO
B. Ca(OH)₂
C. NaOH
D. HCl
Answer: B
FAQ Section
Q1. What is the pH of a neutral solution?
Answer: 7
Q2. Which gas is produced when acids react with metals?
Answer: Hydrogen gas.
Q3. Why are acids acidic?
Answer: Because they release H⁺ ions in aqueous solution.
Q4. What is an alkali?
Answer: A base soluble in water.
Q5. What is water of crystallisation?
Answer: Fixed number of water molecules present in one formula unit of a salt.
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