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Indicate the steps in the preparation of K2Cr2O7 from chromite ore. - Chemistry

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ConceptSome Important Compounds of Transition Elements - Oxides and Oxoanions of Metals

Question

Indicate the steps in the preparation of K2Cr2O7 from chromite ore.

Solution

Potassium dichromate (`K_2Cr_2O_7`) is prepared from chromite ore (`FeCr_2O_4`)in the following steps.

Step (1): Preparation of sodium chromate

`4FeCr_2O_4 + 16NaOH + 7O_2 ->8Na_2CrO_4 + 2Fe_2O_3 + 8H_2O`

Step (2): Conversion of sodium chromate into sodium dichromate

`2Na_2CrO_4 + conc.H_2SO_4 -> Na_2Cr_2O_7+Na_2SO_4+H_2O`

Step(3): Conversion of sodium dichromate to potassium dichromate

`Na_2Cr_2O_7 + 2KCl -> K_2Cr_2O_7 + 2NaCl`

Potassium chloride being less soluble than sodium chloride is obtained in the form of orange coloured crystals and can be removed by filtration.

The dichromate ion (`Cr_2O_7^(2-)`) exists in equilibrium with chromate (`CrO_4^(2-)`) ion at pH 4. However, by changing the pH, they can be interconverted.

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 NCERT Solution for Chemistry Textbook for Class 12 (2018 to Current)
Chapter 8: The d-block and f-block Elements
Q: 26.1 | Page no. 235
Solution Indicate the steps in the preparation of K2Cr2O7 from chromite ore. Concept: Some Important Compounds of Transition Elements - Oxides and Oxoanions of Metals.
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