9.5 Specify the oxidation numbers of the metals in the following coordination entities:

(i) [Co(H2O)(CN)(en)2]2+          

(ii) [CoBr2(en)2]+       

(iii) [PtCl4]2–                         

(iv) K3[Fe(CN)6]           

(v) [Cr(NH3)3Cl3]

 
(i) Co(H2O) (CN) (en)22+
Let the oxidation number of Co be x.
The charge on the complex is +2.
Co    H2O    CN     en22+  x    +   0   +  -1  + 20  = +2                     x - 1 = 2                         x = +3
(ii) Pt(CI)42-
Let the oxidation number of Pt be x.
The charge on the complex is −2.
Pt      Cl42-  x  + 4(1) = 2 x           x = + 2
(iii)
 Co       Br2         en22+   x  +  2(-1)   +   2(0) = +1           x - 2 = +1                            x = +3
(iv)   K3 Fe(CN)6
i.e,
 Fe     CN63-   x  +  6(-1) = -3            x = +3
(v)
 Cr       NH33       Cl3    x  + 3(0) +  3(-1) = 0                   x - 3 = 0                   x = +3