What may be the possible oxidation states of the transition metals with the following d electronic configurations for the ground state

Question

(a) What may be the possible oxidation states of the transition metals with the following d
electronic configurations for the ground state of their atoms 3d3 4s2, 3d5 4s2 and 3d6 4s2? Indicate relative stability of oxidation states in each case.

(b) Write steps involved in the preparation of

(i) Na2CrO4 from chromite ore and

(ii) K2MnO4 from pyrolusite ore.

Answer 1

(a) The most stable oxidation state for 3d3 4s2 = +5
The most stable oxidation state for 3d5 4s2 = +7, +2

The most stable oxidation state for 3d6 4s2 = +2
In a transition series, the oxidation states which lead to exactly half-filled or completely filled d- orbitals are more stable. It shows that oxidation states +2 to +7 is most stable.

(b) (i) The powdered chromite ore is heated with sodium carbonate in presence of air to get yellow **** sodium chromite.

(ii) Finally powdered pyrolusite is fused with KOH in the presence of air to give green **** potassium manganate.

2MnO2 + 4 KOH +O2 → 2K2MnO4 + 2H2O.