Question

Which of the following cations are coloured in aqueous solutions and why ?

Sc³⁺, V³⁺, Ti⁴⁺, Mn²⁺ (At. Nos. Sc = 21, V = 23, Ti = 22, Mn = 25)

Answer 1

The color of cations is dependent on the number of unpaired electrons present in d-orbital. The electronic configuration of the following cations is as follows:

Sc (Atomic number 21) = 3d¹ 4s² and Sc³⁺ = 3d⁰ 4s⁰. As d-orbital is empty, it is colourless.

V (Atomic number 23) = 3d³ 4s² and V³⁺ = 3d² 4s⁰. As d-orbital is having 2 unpaired electrons, it undergoes d-d transition and shows green colour.

Ti = (Atomic number 22) = 3d² 4s² and Ti⁴⁺ = 3d⁰ 4s⁰. As d-orbital is empty, it is colourless.

Mn = (Atomic number 25) = 3d⁵ 4s² and Mn²⁺ = 3d⁵ 4s⁰. As d-orbital is having 5 unpaired electrons, it shows pink color.