Describe the preparation of potassium dichromate from iron chromite ore
Answers
Answer:
Preparation of potassium dichromate \displaystyle K_2Cr_2O_7K
2
Cr
2
O
7
from chromite ore \displaystyle FeO \cdot Cr_2O_3 (FeCr_2O_4)FeO⋅Cr
2
O
3
(FeCr
2
O
4
):
(i) Chromite ore is fused with NaOHNaOH or sodium carbonate in air to form sodium chromate.
\displaystyle 4FeCr_2O_4 + 16NaOH + 7O_2 \rightarrow 8Na_2CrO_4 + 2Fe_2O_3 +8H_2O4FeCr
2
O
4
+16NaOH+7O
2
→8Na
2
CrO
4
+2Fe
2
O
3
+8H
2
O
(ii) Sodium chromate solution is filtered and acidified to form sodium dichromate
\displaystyle 2Na_2CrO_4 + H_2SO_4 \rightarrow Na_2Cr_2O_7 + Na_2SO_4 +H_2O2Na
2
CrO
4
+H
2
SO
4
→Na
2
Cr
2
O
7
+Na
2
SO
4
+H
2
O
The solution is cooled to remove crystallized sodium sulphate. Sodium dichromate remains soluble.
(iii) Equimolar proportions of a hot solution of sodium dichromate and KCl are mixed to form potassium dichromate.
\displaystyle Na_2Cr_2O_7 + 2KCl \rightarrow K_2Cr_2O_7 + 2 NaClNa
2
Cr
2
O
7
+2KCl→K
2
Cr
2
O
7
+2NaCl