Question 33 of 44intermediate🔧 ApplyLong Answer5 marks

Indicate the steps in the preparation of:

(i)

K_2Cr_2O_7 from chromite ore.

Answer

Step 1 - Fusion of Chromite Ore: Chromite ore (FeCr₂O₄) is fused with sodium carbonate (Na₂CO₃) in the presence of oxygen (air) at high temperature.

4FeCr2O4+8Na2CO3+7O2→8Na2CrO4+2Fe2O3+8CO24 \text{FeCr}_2\text{O}_4 + 8 \text{Na}_2\text{CO}_3 + 7 \text{O}_2 \rightarrow 8 \text{Na}_2\text{CrO}_4 + 2 \text{Fe}_2\text{O}_3 + 8 \text{CO}_2

Step 2 - Filtration: The yellow solution of sodium chromate (Na₂CrO₄) is filtered to remove insoluble ferric oxide.

Step 3 - Acidification: The sodium chromate solution is acidified with sulphuric acid to give orange sodium dichromate (Na₂Cr₂O₇·2H₂O).

2Na2CrO4+2H+→Na2Cr2O7+2Na++H2O2\text{Na}_2\text{CrO}_4 + 2 \text{H}^+ \rightarrow \text{Na}_2\text{Cr}_2\text{O}_7 + 2 \text{Na}^+ + \text{H}_2\text{O}

Note: The provided context shows preparation up to sodium dichromate. The conversion to potassium dichromate (K₂Cr₂O₇) is not included in the context.

(ii)

KMnO_4 from pyrolusite ore.

Answer

The provided context does not contain the preparation steps for KMnO₄ from pyrolusite ore. The context only includes reactions showing permanganate (MnO₄⁻) acting as an oxidizing agent in acidic, neutral, and alkaline media with various substances like oxalate, hydrogen sulphide, sulphite, nitrite, iodide, and thiosulphate.

Explanation

The context provides detailed steps for the preparation of sodium dichromate from chromite ore, including the fusion reaction with sodium carbonate and subsequent acidification. However, it does not include the final conversion step to potassium dichromate. For potassium permanganate preparation, the context is incomplete - it mentions Question 4.16 which asks about KMnO₄ preparation, but the actual preparation steps from pyrolusite ore are not provided in the retrieved chunks. The context only shows permanganate's oxidizing reactions.

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