Question

Balance the following redox reaction by oxidation number method mno2+Br mn2+Br2+H2O (acid medium)

Answer 1

Answer:

MnO

4

−

+Br

−

→Mn

2+

+Br

2

(a) First half reaction;

M

+7

nO

4

−

→

M

+2

n

2+

To balance oxygen atoms, H

2

O is added on right side,

MnO

4

−

→Mn

2+

+4H

2

O

(b) To balance hydrogen, H+ ions are added to left side

MnO

4

−

+8H

+

→5e

−

→Mn

2+

+4 H

2

O

Second half reaction

B

−1

r

−

→

B

0

r

2

Or 2Br

−

→Br

2

To balance charge, 2

e

−

are added right hand side

2Br

−

→Br

2

+2

e

−

Now adding the equation (i) (ii)

2MnO

4

−

+16H

+

+10Br

−

⟶2Mn

2+

+8H

2

O+5Br

2

MnO

4

−

+8H

+

+5

e

−

⟶Mn

2+

+4H

2

O×22Br

−

⟶Br

2

+2

e

−

×5

This is balanced equation.