Question

What is the oxidation state of Co in the complex, [Co(NH₃)₂(NO₂)Cl][Au(CN)₂]?

Answer 1

The oxidation state of Co in the complex:

[Co(NH₃)₂(NO₂)Cl][Au(CN)₂]

The complex has two parts:

1. Cation: [Co(NH₃)₂(NO₂)Cl]⁺
2. Anion: [Au(CN)₂]⁻

Since the anion [Au(CN)₂]⁻ has a –1 charge, the cation [Co(NH₃)₂(NO₂)Cl]⁺ must have a +1 charge to balance the overall charge (because the salt is neutral).

In the cation [Co(NH₃)₂(NO₂)Cl]⁺:

• NH₃ (ammonia) is neutral → charge = 0

• NO^2– (nitrito) is –1 → charge = –1

• Cl^– (chloride) is –1 → charge = –1

Let the oxidation state of Co be x.

x + 2(0) + (–1) + (–1) = +1

x – 2 = +1

x = +3