<h2>What is Ionic Equilibrium?</h2> <p>Ionic equilibrium deals with the equilibrium established between ions and molecules in an aqueous solution. It is one of the most high-weightage chapters in NEET Chemistry, typically contributing 2–3 questions every year.</p> <h2>Strong vs Weak Electrolytes</h2> <p><strong>Strong electrolytes</strong> (HCl, NaOH, NaCl) dissociate completely in water. <strong>Weak electrolytes</strong> (CH₃COOH, NH₄OH) partially dissociate and establish an equilibrium described by the dissociation constant <em>Ka</em> (for acids) or <em>Kb</em> (for bases).</p> <h2>pH Scale</h2> <p>pH = −log[H⁺]. At 25°C, neutral water has pH = 7. For strong acid HCl at 0.01 M: pH = −log(0.01) = 2.</p> <p>For weak acid HA with concentration C and Ka: [H⁺] ≈ √(Ka × C), so pH ≈ ½(pKa − log C).</p> <h2>Buffer Solutions</h2> <p>A buffer resists change in pH. The Henderson–Hasselbalch equation:</p> <pre>pH = pKa + log([A⁻]/[HA])</pre> <p>Common buffers in NEET: CH₃COONa/CH₃COOH (acidic buffer) and NH₄Cl/NH₃ (basic buffer).</p> <h2>Common-Ion Effect</h2> <p>Adding a common ion suppresses ionisation. Adding NaCl to CH₃COOH decreases [CH₃COO⁻] and shifts equilibrium left, reducing ionisation.</p> <h2>Solubility Product (Ksp)</h2> <p>For AgCl ⇌ Ag⁺ + Cl⁻: Ksp = [Ag⁺][Cl⁻]. If ionic product Q > Ksp, precipitation occurs.</p> <p><strong>Solubility (s) from Ksp:</strong> For AB type, s = √Ksp. For AB₂ type (e.g., PbCl₂), Ksp = 4s³, so s = (Ksp/4)^(1/3).</p> <h2>Salt Hydrolysis</h2> <p>Salts of weak acid + strong base (e.g., CH₃COONa) give basic solution. Salts of strong acid + weak base (e.g., NH₄Cl) give acidic solution. pH for hydrolysed salt: pH = 7 + ½(pKa − pKb).</p> <h2>NEET Previous Year Trends</h2> <ul> <li>pH of buffer with given concentrations (almost every year)</li> <li>Identifying whether precipitation occurs using Ksp</li> <li>Degree of hydrolysis and pH of salt solutions</li> </ul>