Predict which of the following will be coloured in aqueous solution? Ti3+ ,V3+ , Cu+ , Sc3+ , Mn2+ , Fe3+ and Co2+ . Give reasons for each.
Predict which of the following will be coloured in aqueous solution? Ti3+ ,V3+ , Cu+ , Sc3+ , Mn2+ , Fe3+ and Co2+ . Give reasons for each.
Solution and Explanation
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.
| Element | Atomic Number | Ionic State | Electronic configuration in ionic state |
| Ti | 22 | Ti3+ | [Ar] 3d1 |
| V | 23 | V3+ | [Ar] 3d2 |
| Cu | 29 | Cu+ | [Ar] 3d10 |
| Sc | 21 | Sc3+ | [Ar] |
| Mn | 25 | Mn2+ | [Ar] 3d5 |
| Fe | 26 | Fe3+ | [Ar] 3d5 |
| Co | 27 | Co2+ | [Ar] 3d7 |
From the above table, it can be easily observed that only Sc3+ has an empty d-orbital and Cu+ has completely filled d-orbitals. All other ions, except Sc3+ and Cu+, will be coloured in aqueous solution because of d-d transitions.
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Concepts Used:
D and F Block Elements
The d-block elements are placed in groups 3-12 and F-block elements with 4f and 5f orbital filled progressively. The general electronic configuration of d block elements and f- block elements are (n-1) d 1-10 ns 1-2 and (n-2) f 1-14 (n-1) d1 ns2 respectively. They are commonly known as transition elements because they exhibit multiple oxidation states because of the d-d transition which is possible by the availability of vacant d orbitals in these elements.
They have variable Oxidation States as well as are good catalysts because they provide a large surface area for the absorption of reaction. They show variable oxidation states to form intermediate with reactants easily. They are mostly lanthanoids and show lanthanoid contraction. Since differentiating electrons enter in an anti-penultimate f subshell. Therefore, these elements are also called inner transition elements.
Read More: The d and f block elements