Board exam focus — Acids, Bases and Salts (CBSE & HBSE)

Covers identification, chemical properties, and pH importance. CBSE focuses on pH in daily life and salt preparation; HBSE focuses on indicators and reaction formulas.

Indicators and Physical Properties

Acids are sour in taste and turn blue litmus red. Bases are bitter in taste and turn red litmus blue.

Comparison Table: Acids vs Bases

Indicators

Substances which change their color or odor in different types of substances (Acids/Bases).

• Natural Indicators: Litmus (Lichen), Turmeric.
• Synthetic Indicators: Methyl Orange, Phenolphthalein.
• Olfactory Indicators: Odor changes in acid/base media. Example: Vanilla, Onion, Clove.

Diagram Indicator: [Illustration of pH scale from 0-14 showing common substances like lemon (acidic) and soap (basic).]

Chemical Properties of Acids and Bases

Acids and bases show specific chemical behaviors when reacting with other substances.

1. Reaction with Metals

• Acid + Metal → Salt + Hydrogen Gas
• Example: Zn + H₂SO₄ → ZnSO₄ + H₂
• Base + Metal → Salt + Hydrogen Gas
• Example: 2NaOH + Zn → Na₂ZnO₂ (Sodium Zincate) + H₂

2. Reaction with Metal Carbonates & Hydrogen Carbonates

• Metal Carbonate + Acid → Salt + CO₂ + H₂O
• Example: Na₂CO₃ + 2HCl → 2NaCl + H₂O + CO₂

3. Neutralisation Reaction

Reaction between an acid and a base to give a salt and water.

• Base + Acid → Salt + Water
• Example: NaOH(aq) + HCl(aq) → NaCl(aq) + H₂O(l)

pH Scale and its Importance

The strength of acid or base solutions is measured using the pH scale (0-14).

• pH < 7: Acidic solution.
• pH = 7: Neutral solution (Pure water).
• pH > 7: Basic solution.

Importance in Everyday Life:

1. Digestive System: Our stomach produces HCl (pH ≈ 1.2) to help digest food. Excess acid causes pain (Acidity), treated with Antacids (Magnesium Hydroxide).
2. Tooth Decay: Starts when mouth pH is lower than 5.5. Bacteria produce acids from sugar.
3. Soil pH: Plants require a specific pH range for healthy growth.
4. Self Defense: Bee sting injects methanoic acid (treat with baking soda).

Salts and Their Uses

Salts are formed by neutralisation. Common salt (NaCl) is a raw material for many chemicals.

Key Chemicals from NaCl:

1. Sodium Hydroxide (NaOH): Prepared by the Chlor-alkali process (Electrolysis of Brine).
2. Bleaching Powder (CaOCl₂): Action of chlorine on dry slaked lime.

• Use: Bleaching cotton/linen, disinfecting water.

1. Baking Soda (NaHCO₃): Sodium Hydrogen Carbonate.

• Use: Making crispy pakoras, baking cakes (releases CO₂), as an antacid.

1. Washing Soda (Na₂CO₃·10H₂O): Recrystallization of sodium carbonate.

• Use: Glass/soap industry, removing permanent hardness of water.

Water of Crystallisation

Water of crystallisation is the fixed number of water molecules present in one formula unit of a salt.

• Copper Sulphate: CuSO₄·5H₂O (Blue). On heating, it loses water and turns white.
• Gypsum: CaSO₄·2H₂O.

Plaster of Paris (POP)

On heating Gypsum at 373 K, it loses water molecules and becomes Calcium Sulphate Hemihydrate (CaSO₄·1/2H₂O).

• When mixed with water, it changes back to Gypsum (Hard mass).
• Uses: Supporting fractured bones, making toys, decorative materials.

Frequently asked questions

Are these Acids, Bases and Salts notes free?

Yes — the Acids, Bases and Salts notes for Science (Class 10) on Siksha Sarovar are completely free to read, with no account required.

Do these notes follow CBSE and HBSE?

Yes. The Acids, Bases and Salts notes are NCERT-aligned and include guidance for both CBSE and Haryana Board (HBSE), with important questions and MCQs for revision.

What does the Acids, Bases and Salts chapter cover?

Concept explanations, key formulas and definitions, fully solved examples and board-pattern practice questions for Acids, Bases and Salts.