ICSE Class 10 Chemistry: Acids, Bases & Salts — Notes 2026

Arrhenius Theory of Acids and Bases

• Acid: produces H⁺ ions in water; base: produces OH⁻ ions in water
• Strong acids (HCl, H₂SO₄, HNO₃) fully ionise; weak acids (acetic, carbonic) partially
• Strong bases: NaOH, KOH; weak base: NH₄OH

Indicators and pH Scale

• Litmus: red in acid, blue in base; universal indicator gives pH colour spectrum
• pH scale: 0–14; pH < 7 acidic, pH = 7 neutral, pH > 7 alkaline
• Calculating pH: pH = −log[H⁺]; pH of 0.01 M HCl = 2

Reactions of Acids

• With metals: acid + metal → salt + H₂; Zn + H₂SO₄ → ZnSO₄ + H₂↑
• With metal oxides (bases): acid + base oxide → salt + water
• With carbonates: acid + CaCO₃ → salt + H₂O + CO₂↑

Reactions of Bases

• With acids (neutralisation): NaOH + HCl → NaCl + H₂O; heat released
• With non-metal oxides: Ca(OH)₂ + CO₂ → CaCO₃ + H₂O (limewater test)
• With ammonium salts: NaOH + NH₄Cl → NaCl + H₂O + NH₃↑ (damp red litmus turns blue)

Salts — Types and Preparation

• Acidic salts, basic salts, normal salts, double salts
• Methods: neutralisation, direct combination, action of acid on metal/oxide/carbonate
• Salt hydrolysis: why Na₂CO₃ is alkaline; NH₄Cl is acidic in solution

Analytical Tests for Gases

• H₂: pops with lighted splint; O₂: relights glowing splint
• CO₂: turns limewater milky; SO₂: turns acidified K₂Cr₂O₇ green; HCl: white fumes with NH₃
• NH₃: turns moist red litmus blue; pungent smell

Exam Practice — Acids, Bases, Salts

• Write balanced equation: reaction of dil. H₂SO₄ with excess Zn
• Explain why a solution of Na₂CO₃ is alkaline (salt hydrolysis)
• Identify unknown: acidic gas that decolourises potassium permanganate solution