Following are the transition metal ions of 3d series:
Ti4+, V2+, Mn3+, Cr3+
(Atomic numbers: Ti = 22, V = 23, Mn = 25, Cr = 24)
Answer the following:
1) Which ion is most stable in an aqueous solution and why?
2) Which ion is a strong oxidising agent and why?
3) Which ion is colourless and why?
Solution
1)
| Gaseous ions | Number of unpaired electrons |
| Ti4+, [Ar] 3d0 | 0 |
| V2+, [Ar] 3d3 | 3 |
| Mn3+, [Ar] 3d4 | 4 |
| Cr3+, [Ar] 3d3 | 3 |
V2+ and Cr3+ are the most stable ions in aqueous solutions owing to `t_(2g)^3` a configuration.
2) An examination of the Eo values for the redox couple M3+/M2+ (from electrode potential table) shows that Mn3+ ion are the strongest oxidising agents in aqueous solutions.
3) Only the ions that have electrons in d-orbital and in which d-d transition is possible will be coloured. The ions in which d-orbitals are empty or completely filled will be colourless as no d-d transition is possible in those configurations.
From the given transition metal ions, it can be easily observed that only Ti4+ has an empty d-orbital, so, it is colourless ion.
