Question

vii. The oxidation state of cobalt in complex [CO(NH3)sBr]SO4 is
(a) +2
(b) +3
(c) +1
(d) +4
​

Answer 1

The complex is [Co(NH3)5Br]SO4.

This complex will obviously be a stable molecule having a net charge of zero.

Let the oxidation state of cobalt be x in this complex.

The oxidation state N is -3 .

The oxidation state of H is +1.

That of Br is -1.

That of Oxygen is -2.

That of sulphur in sulphate radical is +6 .

We now form an equation to find the oxidation state of Co.

x - 3 X 5 +1 X 3 x 5 -1 + 6 -2 X 4 =0

x -15 +15 -1 + 6 -8 =0

x - 1 -2 =0

x -3 =0

x= +3

Hence, the oxidation state of Cobalt is +3 (Co3+ ions)

So, the correct option is b) +3