CBSE Class 10 Science Notes – Acids, Bases and Salts (Chapter 2) PDF + Important Questions 2026

CBSE Class 10 Science Notes – Acids, Bases and Salts

Class 10 Chemistry | NCERT Chapter 2 | Board Exam Weightage: 6-8 Marks

CBSE Class 10 Notes for Chapter 2 provide complete coverage of the NCERT syllabus with exam-focused explanations. These CBSE Class 10 Science Notes include properties of acids and bases, pH scale, salts, chlor-alkali process, and chemicals from common salt with solved examples.

1. Introduction

Acids are substances that taste sour, turn blue litmus red, and produce hydrogen ions (H⁺) in aqueous solution. Bases taste bitter, feel soapy, turn red litmus blue, and produce hydroxide ions (OH⁻) in solution. Salts are ionic compounds formed by neutralization of acids and bases.

Everyday Examples:

• Acids: Lemon (citric acid), vinegar (acetic acid), curd (lactic acid), tamarind (tartaric acid)
• Bases: Soap (sodium/potassium salts), baking soda (sodium bicarbonate), lime water (calcium hydroxide)
• Salts: Common salt (NaCl), baking powder, bleaching powder

Why This Chapter Matters:

• Board Exam Weightage: 6-8 marks (Theory + Practical)
• High-scoring: pH scale, chemical reactions, salt preparation equations
• Foundation for understanding chemical behavior
• NCERT Chapter 2: Acids, Bases and Salts (2024-25 Edition)

2. Chapter Overview

CBSE Class 10 Science Notes for this chapter cover:

• Properties of acids and bases
• Chemical reactions of acids and bases (with metals, carbonates, each other)
• Strength of acids and bases (concentrated vs dilute, strong vs weak)
• pH scale and its importance in daily life
• Salts and their family (acidic, basic, neutral salts)
• Chemicals from common salt (Chlor-alkali process)
• Preparation and uses of washing soda and baking soda

3. CBSE Class 10 Science Notes – Properties of Acids & Bases

Acids

Acids are substances that produce hydrogen ions (H⁺) or hydronium ions (H₃O⁺) when dissolved in water.

HCl(g) + H₂O(l) → H₃O⁺(aq) + Cl⁻(aq)

Physical Properties of Acids

• Sour taste
• Turn blue litmus paper red
• Conduct electricity in aqueous solution (electrolytes)
• pH less than 7

Chemical Properties of Acids

1. Reaction with Metals: Acids react with active metals to produce salt and hydrogen gas

2Na(s) + 2HCl(aq) → 2NaCl(aq) + H₂(g)↑

Zn(s) + H₂SO₄(aq) → ZnSO₄(aq) + H₂(g)↑

Test for H₂ gas: Burning candle brought near gas produces 'pop' sound

2. Reaction with Metal Carbonates and Hydrogen Carbonates: Produce salt, water and carbon dioxide gas

Na₂CO₃(s) + 2HCl(aq) → 2NaCl(aq) + H₂O(l) + CO₂(g)↑

NaHCO₃(s) + HCl(aq) → NaCl(aq) + H₂O(l) + CO₂(g)↑

Test for CO₂ gas: Turns lime water milky (Ca(OH)₂ + CO₂ → CaCO₃↓ + H₂O)

3. Reaction with Metal Oxides: Produce salt and water (neutralization)

CuO(s) + 2HCl(aq) → CuCl₂(aq) + H₂O(l)

4. Reaction with Bases: Neutralization reaction (see Section 4)

Bases

Bases are substances that produce hydroxide ions (OH⁻) when dissolved in water.

Physical Properties of Bases

• Bitter taste
• Soapy touch
• Turn red litmus paper blue
• Conduct electricity in aqueous solution
• pH greater than 7

Chemical Properties of Bases

1. Reaction with Metals: Certain metals (Zn, Al) react with strong bases to produce salt and hydrogen

2NaOH(aq) + Zn(s) → Na₂ZnO₂(aq) + H₂(g)↑
(Sodium zincate)

2NaOH(aq) + 2Al(s) + 2H₂O(l) → 2NaAlO₂(aq) + 3H₂(g)↑
(Sodium aluminate)

2. Reaction with Non-metal Oxides: Produce salt and water

2NaOH(aq) + CO₂(g) → Na₂CO₃(aq) + H₂O(l)

3. Reaction with Acids: Neutralization reaction

Key Difference: Acids vs Bases

Property	Acids	Bases
Ions produced	H⁺ / H₃O⁺	OH⁻
Taste	Sour	Bitter
Touch	Not soapy	Soapy
Litmus test	Blue → Red	Red → Blue
pH	< 7	> 7

4. CBSE Class 10 Science Notes – pH Scale & Strength

What is pH?

The pH is a measure of hydrogen ion concentration in a solution. It is defined as the negative logarithm of H⁺ ion concentration:

pH = -log[H⁺]

pH Scale (0 to 14)

• pH = 7: Neutral (pure water, NaCl solution)
• pH < 7: Acidic (lower pH = stronger acid)
• pH > 7: Basic/Alkaline (higher pH = stronger base)

pH Values of Common Substances:

• Gastric juice: 1-2 (strongly acidic)
• Lemon juice: 2-3
• Vinegar: 3-4
• Tomato juice: 4-5
• Milk: 6.5-6.8 (slightly acidic)
• Pure water: 7 (neutral)
• Blood: 7.35-7.45 (slightly basic)
• Baking soda: 8-9
• Soap: 9-10
• Household ammonia: 11-12
• Drain cleaner: 13-14 (strongly basic)

Strong vs Weak Acids and Bases

Type	Strong	Weak
Acids	HCl, H₂SO₄, HNO₃ (complete dissociation)	CH₃COOH, Citric acid (partial dissociation)
Bases	NaOH, KOH, Ca(OH)₂ (complete dissociation)	NH₄OH, Mg(OH)₂ (partial dissociation)

Importance of pH in Daily Life

1. pH in Our Digestive System

The stomach produces hydrochloric acid (pH 1-2) to digest food and kill bacteria. If excess acid is produced, it causes acidity and indigestion. Antacids (milk of magnesia, baking soda) are used to neutralize this excess acid.

2. pH and Tooth Decay

Bacteria in mouth produce acids by degradation of sugar and food particles. When pH in mouth drops below 5.5, tooth enamel (calcium phosphate) starts corroding. Toothpastes are basic to neutralize this acid.

3. pH of Soil

Plants require specific pH range for healthy growth:

• Most plants: pH 6-7.5
• If soil is acidic: Add slaked lime (Ca(OH)₂) or chalk (CaCO₃)
• If soil is basic: Add organic matter (compost) which releases acids

4. pH of Water Bodies

Aquatic life requires pH 7-8.5. If water becomes too acidic (acid rain, industrial waste), aquatic life is threatened.

5. pH of Blood

Human blood maintains pH 7.35-7.45. Even small changes can be fatal. Buffers in blood maintain this pH.

5. CBSE Class 10 Science Notes – Salts & Chemicals from Common Salt

Definition of Salts

Salts are ionic compounds formed by neutralization reaction between acids and bases. They are composed of positive ions (cations) from bases and negative ions (anions) from acids.

Acid + Base → Salt + Water

Family of Salts

Salts having the same positive or negative radicals belong to the same family:

• Sodium salts family: NaCl, Na₂SO₄, Na₂CO₃, NaHCO₃
• Chloride salts family: NaCl, KCl, CaCl₂, NH₄Cl
• Sulphate salts family: Na₂SO₄, CuSO₄, ZnSO₄

Types of Salts Based on Strength

Type	Formation	pH	Examples
Neutral Salt	Strong acid + Strong base	= 7	NaCl, KNO₃, Na₂SO₄
Acidic Salt	Strong acid + Weak base	< 7	NH₄Cl, (NH₄)₂SO₄
Basic Salt	Weak acid + Strong base	> 7	Na₂CO₃, CH₃COONa, NaHCO₃

Chlor-Alkali Process

The Chlor-alkali process is an industrial method for producing sodium hydroxide (NaOH), chlorine gas (Cl₂), and hydrogen gas (H₂) by electrolysis of concentrated aqueous sodium chloride solution (brine).

2NaCl(aq) + 2H₂O(l) → 2NaOH(aq) + Cl₂(g) + H₂(g)

Process Details:

1. Brine preparation: Saturated NaCl solution
2. Electrolysis: Pass electricity through brine in electrolytic cell
3. At anode (positive electrode): Chlorine gas is evolved
   2Cl⁻ → Cl₂ + 2e⁻
4. At cathode (negative electrode): Hydrogen gas is evolved
   2H⁺ + 2e⁻ → H₂
5. In solution: Na⁺ and OH⁻ remain, forming NaOH

Products and Their Uses:

Product	Uses
Sodium hydroxide (NaOH)	Soaps, detergents, paper, artificial fibers, petroleum refining
Chlorine (Cl₂)	Water treatment, PVC, chloroform, bleaching powder, CFCs
Hydrogen (H₂)	Margarine, ammonia synthesis, rocket fuel, hydrogenation of oils

Important Chemicals from Common Salt

1. Sodium Hydroxide (NaOH) - Caustic Soda

Preparation: Chlor-alkali process (as described above)

Properties: White crystalline solid, hygroscopic, corrosive, soapy touch

Uses: Soap and detergent manufacturing, paper industry, petroleum refining, degreasing metals

2. Bleaching Powder (CaOCl₂)

Preparation: By passing chlorine gas through dry slaked lime

Ca(OH)₂(s) + Cl₂(g) → CaOCl₂(s) + H₂O(l)

Chemical name: Calcium oxychloride

Uses: Bleaching cotton and linen in textile industry, disinfecting water, making chloroform

3. Baking Soda (NaHCO₃) - Sodium Bicarbonate

Preparation: By passing CO₂ through ammoniacal brine (Solvay process)

NaCl + NH₃ + CO₂ + H₂O → NaHCO₃ + NH₄Cl

Properties: White crystalline solid, mild non-corrosive base

Uses:

• As baking powder (mixed with tartaric acid)
• Antacid to neutralize stomach acid
• Soda-acid fire extinguishers
• Making soft drinks

4. Washing Soda (Na₂CO₃·10H₂O) - Sodium Carbonate Decahydrate

Preparation: By heating baking soda and then crystallizing

2NaHCO₃ → Na₂CO₃ + H₂O + CO₂ (on heating)

Na₂CO₃ + 10H₂O → Na₂CO₃·10H₂O (crystallization)

Properties: Transparent crystalline solid, efflorescent (loses water of crystallization)

Uses:

• Manufacturing glass, soap, paper
• Removing permanent hardness of water
• Laundry (cleaning clothes)

Baking Soda vs Washing Soda - Memory Trick:

Baking Soda = Bread Softener (for cooking)

Washing Soda = Water Softener (for cleaning)

Or: Baking = 1 carbon (NaHCO₃), Washing = 2 carbons (Na₂CO₃)

6. Important Points (Quick Revision)

• pH Scale: 0-6 acidic, 7 neutral, 8-14 basic
• Neutralization: Acid + Base → Salt + Water + Heat
• Strong acids: HCl, H₂SO₄, HNO₃ (complete ionization)
• Weak acids: CH₃COOH, citric acid (partial ionization)
• Chlor-alkali process: Electrolysis of brine → NaOH + Cl₂ + H₂
• Baking soda: NaHCO₃, used in baking powder and antacids
• Washing soda: Na₂CO₃·10H₂O, used in glass and soap industry
• Bleaching powder: CaOCl₂, used for bleaching and disinfection

7. Solved Examples (CBSE Pattern)

Example 1: pH-Based Question (2 Marks)

Question: Five solutions A, B, C, D and E showed pH values of 4, 1, 11, 7 and 9 respectively when tested with universal indicator. Identify:

a) Neutral solution

b) Strongly alkaline solution

c) Strongly acidic solution

d) Weakly acidic solution

e) Weakly alkaline solution

Solution:

• a) D (pH = 7) - Neutral
• b) C (pH = 11) - Strongly alkaline
• c) B (pH = 1) - Strongly acidic
• d) A (pH = 4) - Weakly acidic
• e) E (pH = 9) - Weakly alkaline

Example 2: Reaction with Metal (2 Marks)

Question: A metal compound 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.

Solution:

The gas that extinguishes candle is CO₂. The metal compound is calcium carbonate (CaCO₃).

CaCO₃(s) + 2HCl(aq) → CaCl₂(aq) + H₂O(l) + CO₂(g)↑

Example 3: Identify Acid/Base (3 Marks)

Question: How would you distinguish between baking soda and washing soda using a simple test?

Solution:

Heating Test:

• Baking soda (NaHCO₃): On heating, it decomposes giving off CO₂ gas (turns lime water milky) and water vapor
• Washing soda (Na₂CO₃·10H₂O): On heating, it loses water of crystallization (efflorescence) but no gas evolution

2NaHCO₃ → Na₂CO₃ + H₂O + CO₂↑ (Baking soda)

Na₂CO₃·10H₂O → Na₂CO₃ + 10H₂O (Washing soda)

Example 4: Equation-Based Question (3 Marks)

Question: Write balanced chemical equations for:

a) Chlorine gas is passed through dry slaked lime

b) Sodium hydroxide solution reacts with hydrochloric acid

c) Zinc metal reacts with sodium hydroxide

Answers:

a) Ca(OH)₂ + Cl₂ → CaOCl₂ + H₂O (Bleaching powder)

b) NaOH + HCl → NaCl + H₂O (Neutralization)

c) 2NaOH + Zn → Na₂ZnO₂ + H₂↑ (Sodium zincate)

Example 5: 5-Mark Conceptual Question

Question: a) What is chlor-alkali process? Write the chemical equation.

b) Name the three products obtained and give one use of each.

c) Why is this process named so?

a) Chlor-alkali process: Electrolysis of concentrated aqueous sodium chloride (brine) to produce sodium hydroxide, chlorine gas and hydrogen gas.

2NaCl(aq) + 2H₂O(l) → 2NaOH(aq) + Cl₂(g) + H₂(g)

b) Products and uses:

• Sodium hydroxide (NaOH): Making soap and detergents
• Chlorine (Cl₂): Water treatment, PVC production
• Hydrogen (H₂): Hydrogenation of vegetable oils

c) Naming: Named after products - Chlorine and Alkali (NaOH)

Example 6: Case-Study Based Question

Passage: A student observed that fresh milk has pH 6. When it changes into curd, the pH decreases. The milkman adds a small amount of baking soda to fresh milk to increase its pH to slightly alkaline.

Questions: a) Why does pH decrease when milk changes to curd? b) Why does the milkman add baking soda? c) Why does this milk take longer time to set as curd?

a) Milk contains lactic acid bacteria which convert lactose into lactic acid. Acid decreases pH.

b) To shift pH to alkaline so that milk does not set as curd quickly (preservation).

c) The added base (baking soda) neutralizes the lactic acid produced, so more time is needed to produce sufficient acid for curdling.

8. Smart Tricks & Memory Aids

pH Memory Trick:

Acid = Angry (low pH, 0-6)

Base = Big heart (high pH, 8-14)

Neutral = Nice (pH 7)

Or remember: 0-6 ACID, 7 NEUTRAL, 8-14 BASE

Acid-Base Identification Shortcut:

• Sour taste + Blue litmus turns Red = ACID
• Bitter taste + Soapy feel + Red litmus turns Blue = BASE
• Remember: Blue→Red = Boy→Rude (Acid)

Baking Soda vs Washing Soda:

Baking Soda	Washing Soda
NaHCO₃	Na₂CO₃·10H₂O
1 Na, 1 C	2 Na, 1 C
For cooking/baking	For cleaning/washing
Heating → CO₂ released	Heating → Water lost

Chlor-Alkali Memory Trick:

Chlorine + Alkali (NaOH) + Hydrogen

Remember: CAH - Chlorine, Alkali, Hydrogen

Or: Chlorine at Anode, Hydrogen at Cathode

Board Answer-Writing Strategy:

1. Always write word equation before chemical equation
2. Include state symbols (s, l, g, aq) for full marks
3. For pH questions: Mention acidic (<7), basic (>7), neutral (=7)
4. For salt preparation: Write balanced equation + conditions
5. Remember 3 products of chlor-alkali process
6. For identification tests: Write observation + conclusion

9. Visual Learning – Diagrams

Figure 1: pH Scale (0-14) showing Universal Indicator Colors - Acidic (Red), Neutral (Green), Basic (Purple)

ALT: CBSE Class 10 Science Notes Acids Bases and Salts - pH Scale Diagram

Figure 2: Neutralization Reaction - Acid (HCl) + Base (NaOH) → Salt (NaCl) + Water (H₂O)

ALT: CBSE Class 10 Science Notes Acids Bases and Salts - Neutralization Reaction Diagram

Figure 3: Chlor-Alkali Process - Electrolysis of brine showing anode (Cl₂), cathode (H₂), and NaOH formation

ALT: CBSE Class 10 Science Notes Acids Bases and Salts - Chlor Alkali Process Diagram

Figure 4: Manufacturing Process Flow Diagram for Washing Soda (Solvay Process)

ALT: CBSE Class 10 Science Notes Acids Bases and Salts - Washing Soda Preparation Flowchart

10. Most Important Board Questions

1 Mark Questions ★

What is the pH of pure water?

7 (neutral)

Name the gas evolved when zinc reacts with dilute HCl.

Hydrogen gas (H₂)

What is the chemical formula of bleaching powder?

CaOCl₂ (Calcium oxychloride)

What is the common name of NaHCO₃?

Baking soda (Sodium bicarbonate)

2-3 Mark Questions ★★

Why does dry HCl gas not change the color of dry litmus paper?

Dry HCl gas does not contain H⁺ ions. Acids show acidic character only in aqueous solution due to presence of H⁺/H₃O⁺ ions.

Why should curd and sour substances not be kept in brass and copper vessels?

Curd and sour substances contain acids which react with copper/brass to form toxic compounds and hydrogen gas, spoiling the food.

What is neutralization reaction? Give one example.

Reaction between acid and base to form salt and water. Example: NaOH + HCl → NaCl + H₂O

4-5 Mark Questions ★★★

Explain chlor-alkali process with chemical equation. Name the products and their uses.

Electrolysis of brine: 2NaCl + 2H₂O → 2NaOH + Cl₂ + H₂. Products: NaOH (soap), Cl₂ (PVC), H₂ (margarine).

How is baking soda prepared? Write its chemical properties and uses.

Prepared by Solvay process: NaCl + NH₃ + CO₂ + H₂O → NaHCO₃ + NH₄Cl. Uses: Baking powder, antacid, fire extinguishers.

11. Common Mistakes to Avoid

Mistake	Correction
Confusing strong and weak acids	Strong acids completely dissociate (HCl, H₂SO₄); Weak acids partially dissociate (CH₃COOH)
Writing incorrect chemical formulas	Baking soda = NaHCO₃; Washing soda = Na₂CO₃·10H₂O; Bleaching powder = CaOCl₂
Misunderstanding pH scale	Lower pH = stronger acid; Higher pH = stronger base; pH 7 = neutral
Forgetting state symbols	Always include (s), (l), (g), (aq) in final equations
Wrong products in chlor-alkali	Remember: NaOH (solution), Cl₂ (anode), H₂ (cathode)

12. Practice Section

Multiple Choice Questions (MCQs)

Q1. Which of the following has the highest pH value?

1. Lemon juice
2. Vinegar
3. Milk
4. Soap solution

Q2. The product of chlor-alkali process are:

1. NaCl, H₂, O₂
2. NaOH, Cl₂, H₂
3. Na₂CO₃, H₂O, CO₂
4. NaHCO₃, NH₄Cl

Q3. Which salt is used for removing permanent hardness of water?

1. Baking soda
2. Washing soda
3. Bleaching powder
4. Common salt

Assertion-Reason Question

Assertion (A): Toothpaste is basic in nature.

Reason (R): Bacteria in mouth produce acids which cause tooth decay.

Answer: Both A and R are true and R is the correct explanation of A.

Explanation: Bacteria produce acids (pH < 5.5) causing tooth decay. Basic toothpaste neutralizes this acid.

13. Frequently Asked Questions (FAQ)

What is pH scale?

pH scale is a measure of hydrogen ion concentration in a solution, ranging from 0 to 14. pH 7 is neutral, below 7 is acidic, and above 7 is basic. It is defined as pH = -log[H⁺].

What is neutralization reaction?

A reaction in which an acid reacts with a base to form salt and water, with evolution of heat. Example: HCl + NaOH → NaCl + H₂O. The resulting salt may be acidic, basic, or neutral depending on the strength of acid and base.

What is chlor-alkali process?

An industrial process involving electrolysis of concentrated sodium chloride solution (brine) to produce three products: sodium hydroxide (NaOH), chlorine gas (Cl₂), and hydrogen gas (H₂). The chemical equation is: 2NaCl + 2H₂O → 2NaOH + Cl₂ + H₂.

Are these CBSE Class 10 Science Notes based on NCERT?

Yes, these CBSE Class 10 Science Notes are 100% aligned with the latest NCERT textbook (2024-25 edition) for Chapter 2 "Acids, Bases and Salts" and follow the current CBSE syllabus and examination pattern.

How to prevent rusting?

Rusting can be prevented by painting, oiling/greasing, galvanization (zinc coating), electroplating (chromium/nickel), enamel coating, or making alloys like stainless steel. All methods create a barrier between iron and oxygen/moisture.

14. Conclusion

Master Acids, Bases and Salts for Board Success!

These comprehensive CBSE Class 10 Notes for "Acids, Bases and Salts" cover all essential concepts, pH scale, salt preparation, and solved examples to help you excel in your board examinations.

Key Takeaways:

• Understand properties and reactions of acids and bases
• Master pH scale and its importance in daily life
• Remember chlor-alkali process and its three products
• Practice chemical equations with state symbols
• Distinguish between baking soda and washing soda

Next Chapter: Metals and Non-metals – CBSE Class 10 Notes

Best of luck for your CBSE Class 10 Board Examinations!

These CBSE Class 10 Science Notes are prepared by experienced Chemistry faculty following the latest NCERT curriculum.