Question

Illustrate with example, the difference between a double salt and coordination

Answer 1

Hint: Double salt and coordination compounds can be compared on the basis of their chemical and physical properties, For example: their behaviour after dissolution in water, structure etc.

Complete step by step answer:
Double salts
1. These are generally those molecular or additional compounds which exist in a solid state but dissociate into constituent ions when dissolved in water. What we can say is that double salts tend to lose their identity when dissolved in water.
2. EXAMPLE: Mohr’s salt ${\text{FeS}}{{\text{O}}_{\text{4}}}{{\text{(N}}{{\text{H}}_{\text{4}}}{\text{)}}_{\text{2}}}{\text{S}}{{\text{O}}_{\text{4}}}{\text{.6}}{{\text{H}}_{\text{2}}}{\text{O}}$
So, when the Mohr’s salt is dissolved in water it will dissociate to give ions ${\text{F}}{{\text{e}}^{{\text{2 + }}}}{\text{,N}}{{\text{H}}_{\text{4}}}^{\text{ + }}{\text{,S}}{{\text{O}}_{\text{4}}}^{{\text{2 - }}}$and thus will lose its identity.
3. These only exist in solid state.
4. The properties of double salts are exactly the same as that of constituents.
5. Metal ions in double salts show their normal valence.
Coordination compounds
1. Coordination compounds are those molecular or additional compounds which retain their identity in aqueous solution and show property entirely different from their constituent ions from which it is made.
2. EXAMPLE: Potassium ferrocyanide ${{\text{K}}_{\text{4}}}{\text{[Fe(CN}}{{\text{)}}_{\text{6}}}{\text{]}}$.
3. Coordination compounds can exist in solid as well as in the aqueous and non-aqueous solutions.
4. Their properties are different from their constituents from which they are made.
5. Metal ions in the coordination compounds show two valances that are primary valency and secondary valency satisfied by anions or neutral molecules called ligands.

Note:
Generally, double salts and coordination compounds look exactly the same from the chemical formula but they are actually two different concepts in themselves as they differ in physical properties and chemical behaviour.