🧪 Class 10 Chemistry Chapter 2: Acids, Bases, and Salts –Notes

 Welcome back, Class 10 students!

Let’s dive into the world of acids, bases, and salts — one of the most important and interesting chapters in your Chemistry syllabus. This chapter explains what acids and bases are, how they behave, and how salts are formed. Plus, we'll explore real-life examples and reactions!

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🔍 What Are Acids and Bases?

📌 Acids

Acids are substances that taste sour and release H⁺ ions in aqueous solution.

Examples:

• Hydrochloric acid (HCl)

• Sulphuric acid (H₂SO₄)

• Citric acid (in fruits)

📌 Bases

Bases are substances that taste bitter and release OH⁻ ions in aqueous solution.

Examples:

• Sodium hydroxide (NaOH)

• Magnesium hydroxide (Milk of Magnesia)

• Ammonium hydroxide (NH₄OH)

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🧪 Indicators – Acids vs. Bases

Indicators help detect acids or bases by changing colour.

Indicator	Acid Colour	Base Colour
Litmus	Red	Blue
Methyl Orange	Red	Yellow
Phenolphthalein	Colourless	Pink
China Rose (Natural)	Dark Pink	Green

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⚗️ Reactions of Acids and Bases

1️⃣ Reaction with Metals

Acid + Metal → Salt + Hydrogen gas
Example: Zn + H₂SO₄ → ZnSO₄ + H₂↑

2️⃣ Reaction with Metal Carbonates/Bicarbonates

Acid + Metal carbonate → Salt + CO₂ + H₂O
Example: Na₂CO₃ + HCl → NaCl + CO₂ + H₂O

3️⃣ Neutralization Reaction

Acid + Base → Salt + Water
Example: HCl + NaOH → NaCl + H₂O

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🧫 pH Scale – Power of Hydrogen

• Measures acidity or basicity

• Ranges from 0 to 14

  • pH < 7 → Acidic

  • pH = 7 → Neutral

  • pH > 7 → Basic

Important Fact:
Human body’s ideal pH = 7.4

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🌱 Importance of pH in Daily Life

• Digestion: Stomach has HCl to digest food (pH 1-3)

• Tooth decay: Bacteria lower pH in mouth → tooth enamel corrodes

• Soil pH: Farmers test soil pH to decide fertilizers

• Bee stings/Ant bites: Acidic → treat with base (like baking soda)

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🧂 Salts and Their Uses

🧪 What is a Salt?

Salt is formed when an acid reacts with a base (neutralization reaction).

🧾 Examples of Salts and Uses:

Salt	Chemical Formula	Use
Sodium Chloride	NaCl	Table salt, food
Baking Soda	NaHCO₃	Baking, antacids, fire extinguishers
Washing Soda	Na₂CO₃·10H₂O	Detergents, glass, paper industries
Bleaching Powder	Ca(OCl)Cl	Disinfecting water, bleaching agent

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🧁 Preparation of Salts

1️⃣ Baking Soda (NaHCO₃)

NaCl + H₂O + CO₂ + NH₃ → NH₄Cl + NaHCO₃

2️⃣ Washing Soda (Na₂CO₃·10H₂O)

Formed by heating baking soda and recrystallizing:

NaHCO₃ → Na₂CO₃ → Na₂CO₃·10H₂O

3️⃣ Bleaching Powder (Ca(OCl)Cl)

Ca(OH)₂ + Cl₂ → Ca(OCl)Cl + H₂O

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📌 Conclusion

Understanding acids, bases, and salts is not just essential for exams — it's also useful in daily life, from cooking and cleaning to healthcare and agriculture. Keep the pH in balance and always wear a smile in chemistry class! 😊