Explain the method of preparation of potassium dichromate from mineral
chromite. Write chemical equations involved.
Answers
Answer:
Preparation of Potassium Dichromate – K2Cr2O
2H2O) can be extracted. Now potassium dichromate can be obtained by reacting a solution of sodium dichromate with potassium chloride. Thus, we finally obtain the orange crystals of potassium dichromate.
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Preparation pf potassium dichromate from chromite ore involves following steps:
(i) Conversion of chromite ore to sodium chromate by roasting finely powdered chromite ore with sodium carbonate and quick lime in excess of air.
Chromiteore
4FeCr
2
O
4
+
carbonate
Sodium
8Na
2
CO
3
+7O
2
CaO+air
Ferricoxide
2Fe
2
O
3
+
chromate
Sodium
8Na
2
CrO
4
+8CO
2
(ii) Conversion of sodium chromate to sodium dichromate by the action of conc.H
2
SO
4
.
2Na
2
CrO
4
+
conc.
H
2
SO
4
→
dichromate
Sodium
Na
2
Cr
2
O
7
+Na
2
SO
4
+H
2
O
(iii) Conversion of sodium dichromate to potassium dichromate by treating it with KCl solution.
Na
2
Cr
2
O
7
+2KCl→
dichromate
Potassium
K
2
Cr
2
O
7
+2NaCl
From resulting solution potassium dichromate is crystallised.