Acids, Bases & Salts

Class X · CBSE Science · Chapter 2

⚗️ Acids
H⁺ ions in solution Sour taste pH < 7 Turns blue litmus red Reacts with metals → H₂ gas
STRONG ACID

Hydrochloric Acid — HCl

  • Found in gastric juice (stomach)
  • Completely ionises in water
  • HCl → H⁺ + Cl⁻
  • Used in cleaning metals
STRONG ACID

Sulphuric Acid — H₂SO₄

  • King of chemicals
  • Used in car batteries
  • Highly corrosive, dehydrating
  • H₂SO₄ → 2H⁺ + SO₄²⁻
WEAK ACID

Acetic Acid — CH₃COOH

  • Found in vinegar (5–8%)
  • Partially ionises in water
  • Weak, organic acid
  • Used as food preservative
WEAK ACID

Carbonic Acid — H₂CO₃

  • CO₂ dissolved in water
  • Present in fizzy drinks
  • H₂O + CO₂ ⇌ H₂CO₃
  • Gives soda water its tang

🔴 Litmus Test — Acid

Red litmus
in Acid

Blue litmus
in Acid

🧪 Bases & Alkalis
OH⁻ ions in solution Bitter taste pH > 7 Turns red litmus blue Soapy/slippery feel
STRONG BASE

Sodium Hydroxide — NaOH

  • Common name: Caustic soda
  • Completely dissociates: NaOH → Na⁺ + OH⁻
  • Used in soap/paper making
  • Highly corrosive to skin
STRONG BASE

Calcium Hydroxide — Ca(OH)₂

  • Common name: Slaked lime
  • Used in whitewashing walls
  • Neutralises soil acidity
  • Used in water treatment
WEAK BASE

Ammonium Hydroxide — NH₄OH

  • NH₃ dissolved in water
  • Used in cleaning agents
  • Partially ionises in water
  • Pungent smell
ALKALI NOTE

Alkalis vs Bases

  • All alkalis are bases
  • Not all bases are alkalis
  • Alkali = base soluble in water
  • e.g., Cu(OH)₂ is a base but NOT an alkali

🔵 Litmus Test — Base

Red litmus
in Base

Blue litmus
in Base

📊 pH Scale

Drag or use the slider to explore pH values

01234 56789 1011121314
pH 7
Pure water — perfectly neutral
Pure Water Blood (≈7.4)
ACIDIC (pH < 7)

Acidic Solutions

  • pH 1 — Gastric acid (HCl in stomach)
  • pH 2.5 — Lemon juice
  • pH 3 — Vinegar
  • pH 4.5 — Acid rain (< 5.6)
  • pH 6 — Cow's milk
NEUTRAL (pH = 7)

Neutral Solutions

  • pH 7 — Pure distilled water
  • pH 7 — Common salt solution (NaCl)
  • Equal H⁺ and OH⁻ ions
  • Neither acidic nor basic
BASIC (pH > 7)

Basic Solutions

  • pH 7.4 — Human blood
  • pH 8.5 — Sea water
  • pH 10 — Milk of magnesia
  • pH 11 — Household ammonia
  • pH 13 — Bleach / NaOH
🔥 Key Reactions

Neutralisation Reaction

Acid (HCl)
+
Base (NaOH)
→
Salt + Water
HCl + NaOH → NaCl + H₂O
Acid + Base → Salt + Water (Neutralisation)
🔬 Heat is released (exothermic). Universal indicator turns green at neutralisation (pH 7).

Select a Reaction Type

Zn + H₂SO₄ → ZnSO₄ + H₂↑
🔬 Hydrogen gas is evolved. Burns with a 'pop' sound when tested with a burning splint.
🧂 Important Salts
Acid + Base → Salt + Water Ionic compounds Crystalline structure pH depends on parent

Common Salt

NaCl

Sodium Chloride. Essential for life. Used in food, preservation, Cl₂ production.

Neutral · pH 7

Washing Soda

Na₂CO₃·10H₂O

Sodium Carbonate decahydrate. Used in glass, soap, paper industries. Softens hard water.

Basic · pH > 7

Baking Soda

NaHCO₃

Sodium Hydrogen Carbonate. Used in baking, fire extinguishers, antacids.

Weakly Basic

Bleaching Powder

Ca(OCl)Cl

Calcium Oxychloride. Used for disinfecting water, bleaching cotton/linen.

Basic

Plaster of Paris

CaSO₄·½H₂O

Calcium Sulphate hemihydrate. Used in casts, moulds, chalk. Sets hard on adding water.

Neutral

Copper Sulphate

CuSO₄·5H₂O

Blue vitriol. Used as fungicide, in electroplating. Loses water on heating → white powder.

Acidic · pH < 7

Water of Crystallisation

CuSO₄·5H₂O —heat→ CuSO₄ + 5H₂O
Blue crystals → White powder on heating
🔬 The 5 water molecules are called water of crystallisation. Adding water reverses it back to blue.