balance the following redox by ion-electron method
a)2
4 2 4 Mn aq HSO aq acidic medium 4M
Answers
Answer:
In the ion-electron method (also called the half-reaction method), the redox equation is separated into two half-equations - one for oxidation and one for reduction. Each of these half-reactions is balanced separately and then combined to give the balanced redox equation.
Explanation:
The unbalanced chemical equation is:
MnO
4
−
(aq)+SO
2
(g)→Mn
2+
(aq)+HSO
4
−
(aq)
The oxidation half reaction is
SO
2
(g)+2H
2
O(l)→HSO
4
−
(aq)+3H
+
(aq)+2e
−
(aq).
The reduction half reaction is
MnO
4
−
(aq)→Mn
(
2+)(aq).
In the reduction half reaction, the oxidation number of Mn changes from +7 to +2. Hence, 5 electrons are added to LHS of the reaction.
MnO
4
−
(aq)+5e
−
→Mn
2+
(aq)
Charge is balanced in the reduction half reaction by adding 8 hydrogen ions to LHS.
MnO
4
−
(aq)+5e
−
+8H
+
(aq)→Mn
2+
(aq)
To balance O atoms, 4 water molecules are added on RHS.
MnO
4
−
(aq)+5e
−
+8H
+
(aq)→Mn
2+
(aq)+4H
2
O(l)
To equalize the number of electrons, the oxidation half reaction is multiplied by 5 and the reduction half reaction is multiplied by 2.
5SO
2
(g)+10H
2
O(l)→5HSO
4
−
(aq)+15H
+
(aq)+10e
−
(aq)
2MnO
4
−
(aq)+10e
−
+16H
+
(aq)→2Mn
2+
(aq)
Two half cell reactions are added to obtain a balanced equation.
2MnO
4
−
(aq)+5SO
2
(g)+2H
2
O(l)→2Mn
2+
(aq)+5HSO
4
−
(aq)