Hydrolysis Explained in Sinhala 🇱🇰 | A/L Chemistry Made Easy

HYDROLYSIS – A/L CHEMISTRY SUMMARY Hydrolysis is a chemical reaction in which a substance reacts with water to form new chemical species. In salt hydrolysis, ions of a dissolved salt react with water and may change the pH of the solution. TYPES OF SALT HYDROLYSIS 1. Strong Acid + Strong Base Example: NaCl NaCl → Na⁺ + Cl⁻ Neither ion undergoes significant hydrolysis. The solution is approximately neutral at 25°C (pH = 7). 2. Strong Acid + Weak Base Example: NH₄Cl NH₄Cl → NH₄⁺ + Cl⁻ NH₄⁺ + H₂O ⇌ NH₃ + H₃O⁺ NH₄⁺ reacts with water to produce H₃O⁺, making the solution acidic 3. Weak Acid + Strong Base Example: CH₃COONa CH₃COONa → CH₃COO⁻ + Na⁺ CH₃COO⁻ + H₂O ⇌ CH₃COOH + OH⁻ CH₃COO⁻ reacts with water to produce OH⁻, making the solution basic 4. Weak Acid + Weak Base Example: NH₄CH₃COO Both NH₄⁺ and CH₃COO⁻ undergo hydrolysis. The pH depends on the relative strengths of the parent acid and base. IMPORTANT EQUATIONS Ionic product of water: Kw At 25°C: Kw = 1.0 × 10⁻¹⁴ pH + pOH = 14 pKa + pKb = 14 for a conjugate acid-base pair. Hydrolysis constants: For the conjugate base of a weak acid: Kh = Kw/Ka For the conjugate acid of a weak base: Kh = Kw/Kb For a salt formed from a weak acid and weak base: pH ≈ 7 + ½(pKa − pKb) at 25°C. OTHER EXAMPLES Na₂CO₃ produces a basic solution because CO₃²⁻ reacts with water to form OH⁻. Some aluminium salts produce acidic solutions because hydrated Al³⁺ ions undergo hydrolysis and generate H₃O⁺. HYDROLYSIS BEYOND SALTS • Ester hydrolysis produces a carboxylic acid and an alcohol. • Carbohydrate hydrolysis breaks complex carbohydrates into simpler sugars. • Protein hydrolysis breaks peptide bonds into smaller peptides and amino acids. • Fat hydrolysis produces glycerol and fatty acids. Alkaline hydrolysis produces fatty acid salts. EXAM TIPS • Identify the parent acid and base of the salt. • Identify which ion undergoes hydrolysis. • Producing H₃O⁺ generally makes a solution acidic. • Producing OH⁻ generally makes a solution basic. • Dissolution and hydrolysis are different processes. • Neutrality means the concentrations of H₃O⁺ and OH⁻ are equal. Neutral pH is 7 only at 25°C. REMEMBER Strong acid + strong base = approximately neutral. Strong acid + weak base = acidic. Weak acid + strong base = basic. Weak acid + weak base = depends on relative strengths.