Indicate the steps in the preparation of: (i) K2Cr2O7 from chromite ore. (ii) KMnO4 from pyrolusite ore.

Home » Indicate the steps in the preparation of: (i) K2Cr2O7 from chromite ore. (ii) KMnO4 from pyrolusite ore.

Indicate the steps in the preparation of: (i) K2Cr2O7 from chromite ore. (ii) KMnO4 from pyrolusite ore.

(i) Potassium dichromate ( K₂Cr₂O₇ ) is prepared from chromite ore (FeCr₂O₄) in the following steps.

Step (1): Preparation of sodium chromate

$4FeC{r_2}{O_4} + 16NaOH + 7{O_2} \to 8N{a_2}Cr{O_4} + 2F{e_2}{O_3} + 8{H_{2}}O$

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

$N{a_2}Cr{O_4} + Conc.{H_2}S{O_{4}} \to N{a_2}C{r_2}{O_{3}} + N{a_{2}}S{O_{4}} + {H_{2}}O$

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

$N{a_2}C{r_{2}}{O_7} + 2KCl \to {K_{2}}C{r_2}{O_7} + 2NaCl$

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 Cr₂O₇^2- exists in equilibrium with chromate ion CrO₄^2- at pH 4.

However, by changing the pH, they can be interconverted.

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