Preparation of potassium dichromate from chromite oreक्रोमाइट अयस्क से पोटैशियम डाइक्रोमेट का निर्माणPreparation of potassium dichromate from chromite ore
Class 12 Chemistry · Chapter 4 · interactive diagram
Parts and what they mean
- Chromite ore, FeCr₂O₄ (क्रोमाइट अयस्क, FeCr₂O₄) — The starting ore; chromium is +3 here.
- Step 1: alkaline fusion in air (चरण 1: वायु में क्षारीय संगलन) — 4FeCr₂O₄ + 8Na₂CO₃ + 7O₂ → 8Na₂CrO₄ + 2Fe₂O₃ + 8CO₂. Cr is oxidised from +3 to +6.
- Sodium chromate (yellow) (सोडियम क्रोमेट (पीला)) — Yellow solution of Na₂CrO₄.
- Step 2: acidify (चरण 2: अम्लीकरण) — 2Na₂CrO₄ + 2H⁺ → Na₂Cr₂O₇ + 2Na⁺ + H₂O. Not redox: Cr stays +6.
- Sodium dichromate (orange) (सोडियम डाइक्रोमेट (नारंगी)) — Crystallises as Na₂Cr₂O₇·2H₂O.
- Step 3: add KCl (चरण 3: KCl मिलाइए) — Na₂Cr₂O₇ + 2KCl → K₂Cr₂O₇ + 2NaCl. K₂Cr₂O₇ is less soluble, so it crystallises out.
- Potassium dichromate (पोटैशियम डाइक्रोमेट) — Orange-red crystals; used as a primary standard in volumetric analysis.
Steps
- Fuse chromite with sodium carbonate in free air: yellow sodium chromate forms.
- Filter and acidify with sulphuric acid: orange sodium dichromate.
- Add KCl: less soluble potassium dichromate crystallises.
Original diagram drawn by Simple Learning Hub, based on the NCERT textbook. Report a mistake