Question

What is the original color of $FeS{{O}_{4}}$solution and of $FeC{{l}_{3}}$solution?

Answer 1

Iron (Fe) is the metal of the transition metal series of the d – block. The d – block transition metals have a characteristic of being colored in their ionic forms. The salts of the metals of transition series are colored due to the presence of electrons in the d – orbitals in the metal ions. This makes them colored due to d –d transition.

Complete answer:
The salts of transition metals of the d – block are found to be colored. They are colored due to the presence of unpaired electrons in the d – orbitals. When any ligand approaches the metal, then the splitting of d – orbital occurs. They split into, triply generate (${{t}_{2}}g$), and evenly generate (eg). Due to this d –d transition, the electrons absorb energy and move to higher energy levels, and then comes back to the lower energy level and emits energy in the visible region that appears to be the color of the salts.
The given compounds are of iron metal (Fe) which is also a transition metal. The compound $FeS{{O}_{4}}$is iron (II) sulfate or ferrous sulfate that has a blue – green color solution. While the compound, $FeC{{l}_{3}}$is iron (III) chloride or ferric chloride that has a yellow color solution.
Hence, the original color of $FeS{{O}_{4}}$ solution and of $FeC{{l}_{3}}$ solution is blue – green and yellow respectively.

Note:
As transition metals have variable oxidation states, a roman numeral is written after the metal in their naming to denote and identify the oxidation state of the metal. Iron has two oxidation numbers, +2 and +3, which are called ferrous and ferric respectively. Ferrous sulfate and ferric chloride are both ionic compounds and hence have colored solutions as they dissociate into solutions.