Class 12 Practical Titration | KMnO4 Mohr's Salt | Indian students Guide | Calculations + Viva 2026

The Class 12 Chemistry Practical on titration of KMnO₄ (potassium permanganate) vs Mohr's salt (ferrous ammonium sulfate, FeSO₄·(NH₄)₂SO₄·6H₂O) is a standard redox titration experiment in CBSE and most Indian boards. The goal is usually: Prepare a standard solution of Mohr's salt (e.g., M/20 or 0.05 M). Titrate it against the given KMnO₄ solution to find the molarity and strength (g/L) of KMnO₄. This is a self-indicated titration (KMnO₄ is purple; endpoint is permanent faint pink due to excess MnO₄⁻). Theory & Redox Reaction ---------------------------- Mohr's salt provides Fe²⁺ ions (reducing agent), and KMnO₄ in acidic medium is a strong oxidizing agent (oxidizes Fe²⁺ to Fe³⁺ and reduces MnO₄⁻ to Mn²⁺). Ionic half-reactions (most important for viva): Reduction: MnO₄⁻ + 8H⁺ + 5e⁻ → Mn²⁺ + 4H₂O ---------- (n-factor of KMnO₄ = 5 in acidic medium) Oxidation: Fe²⁺ → Fe³⁺ + e⁻ (n-factor of Fe²⁺ / Mohr's salt = 1) Balanced ionic equation: --------------------------- MnO₄⁻ + 8H⁺ + 5Fe²⁺ → Mn²⁺ + 5Fe³⁺ + 4H₂O Molecular equation (for reference): 2KMnO₄ + 10FeSO₄(NH₄)₂SO₄·6H₂O + 8H₂SO₄ → K₂SO₄ + 2MnSO₄ + 5Fe₂(SO₄)₃ + 10(NH₄)₂SO₄ + 68H₂O Dilute H₂SO₄ is added to provide acidic medium and prevent precipitation of MnO₂. Endpoint: Appearance of permanent faint pink color (self-indicator). Apparatus Required Burette (50 mL), pipette (20 mL or 10 mL), conical flask (250 mL) Measuring/volumetric flask (250 mL), weighing bottle, funnel White glazed tile, burette stand, glass rod Chemicals: Mohr's salt, dilute H₂SO₄ (~1–2 M), given KMnO₄ solution, distilled water Procedure (Step-by-Step) A. Preparation of standard Mohr's salt solution (usually M/20 or 0.05 M in 250 mL) Molar mass of Mohr's salt = 392 g/mol For M/20 solution (0.05 M): Weight required = (392 × 0.05 × 250)/1000 = 4.90 g (approximately 4.9 g for 250 mL) Weigh accurately ~4.90 g Mohr's salt in a weighing bottle. Transfer to 250 mL volumetric flask using funnel. Add small amount of dilute H₂SO₄ (to prevent hydrolysis/oxidation), then add distilled water and shake to dissolve. Make up the volume to the mark with distilled water. Shake well. This is your standard solution (Mohr's salt = reducing agent). B. Titration Rinse and fill the burette with the given KMnO₄ solution (remove air bubbles). Pipette out 10 mL or 20 mL of prepared Mohr's salt solution into a conical flask. Add ~10–20 mL dilute H₂SO₄ (about half test tube) to make the medium acidic. Place the conical flask on a white tile under the burette. Note initial burette reading. Run KMnO₄ from burette slowly into the conical flask with constant gentle swirling. The purple color disappears initially due to reduction; continue until a permanent faint pink color appears throughout the solution (endpoint). Note final burette reading. Volume of KMnO₄ used = final – initial. Repeat for 2–3 concordant readings (difference less than 0.1 mL). Class 12 Chemistry Practical: | Class 12 CBSE Practical | Permanent Pink Endpoint Mohr's Salt vs KMnO4 Redox Titration Class 12 | Molarity & Strength Calculation | Board Practical Class 12 Practical: Determine Molarity of KMnO4 using Mohr's Salt | Full Experiment + Viva Questions #VivaQuestions #ChemistryExperiment #12thChemistry #NEETPreparation #JEEPreparation #PunjabStudent #Ludhiana #SciencePractical    • CBSE PRACTICAL 2026 || HOW TO WRITE ANSWER...