Describe the preparation of potassium perma-
nganate. How does the acidified permanganate
solution react with : (i) iron(II) (ii) SO2 and (iii) oxalic
acid (iv) S203 ion ?
Answers
Answer:
Preparation of potassium permanganate, KMnO
4
from pyrolusite ore MnO
2
.
(i) Pyrolusite ore is fused with KOH (or K
2
CO
3
) in presence of air (or oxidising agents such as KNO
3
or KClO
3
) to give potassium manganate K
2
MnO
4
(green mass).
2MNO
2
+4KOH+O
2
Delta
2K
2
MnO
4
+2H
2
O
(ii) Extraction of green mass with water followed by oxidation with chlorine (or ozone or CO
2
) gives potassium permanganate.
2K
2
MnO
4
+Cl
2
→2KCl+2KMnO
4
On concentrating the solution, dark purple crystals of potassium permanganate separates out.
Note: In neutral or acidic medium, manganate ion will disproportionate to permanganate ion.
3MnO
4
2−
+4H
+
→2MnO
4
−
+MnO
2
+2H
2
O
Convertion of manganate to permanganate can also be carried by electrolytic oxidation.
Reactions of acidified permanganate solution with (i) iron(II) ions (ii) SO
2
and (iii) oxalic acid:
2MnO
4
−
+10Fe
2+
+16H
+
→2Mn
2+
+10Fe
3+
+8H
2
O
2MnO
4
−
+5SO
2
+2H
2
O→5SO
4
2−
+2Mn
2+
+4H
+
2MnO
4
−
+5C
2
O
4
2−
+16H
+
→2Mn
2+
+8H
2
O+10CO
2
Explanation:
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Answer:
acidified permanganate
solution react with :
Preparation of potassium permanganate: Potassium permanganate is prepared by the fusion of MnO2 (pyrolusite) with potassium hydroxide and an oxidizing agent like KNO3 to form potassium manganate (green mass), which disproportionate in a neutral or acidic solution to form permanganate.