Question

transition metal compounds are often brightly colored what is the oxidation number of the specific element in the following compounds?

(a) chromium in Na2CrO4. (yellow)
(b) iron in K3 [Fe (CN)6] (orange)
(c) Cobalt in CoCl2. (blue)
(d) nickel in NiCl2×6 H2O (green)

Answer 1

a) The oxidation state of Na is +1 and oxidation state of oxygen is -2
   2(1) + x + 4(-2) = 0
   x = +6
   Therefore oxidation number of Chromium in Na₂CrO₄ is +6
b) The oxidation number of potassium is +1 and CN is -1
   3(1)+ x + 6(-1) = 0
   x = +3
   Therefore oxidation number of Iron in K₃[Fe(CN)₆] is +3
c) The oxidation number of Cl is -1
   x + 2(-1) = 0
   x= +2
   Therefore the oxidation number of Cobalt in COCl₂ is +2
d) The oxidation number of Cl is -1 , H is +1 & O is -2
   x + 2(-1) + 12 (1) + 6 (-2) = 0
   x = +2
   Therefore the oxidation number of Nickel in NiCl₂.6H₂O is +2