Predict which of the following will be coloured in aqueous solution? Ti3+, V3+, Cu+, Sc3+, Mn2+, Fe3+ and Co2+. Give reasons for each.

Metal ions which have valence electrons in d-orbital and in which d-d transition can take place will be coloured and the metal ions which have completely filled orbital or have d-orbital 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 observed that only Sc3+ and Cu+ have either completely filled d-orbital or empty d-orbital. So, all other ions except Sc3+ and Cu+ will be coloured in aqueous solution because of absorption of radiations which fall in the visible region as on obtaining energy electrons jump from one d-orbital to another.


20