Question

Differentiate between a double salt and a complex.

Hint:

A double salt splits into all its simple ions in water, while a complex ion stays intact in solution.

Answer 1

Step 1: Understanding the Concept:
Both are addition compounds made when two simple salts combine. They differ in what happens when they dissolve in water.

Step 2: Double salt:
A double salt exists only in the solid state. In water it breaks up completely into its simple ions. It loses its identity in solution.
Example: Mohr salt, \( \mathrm{FeSO_4 \cdot (NH_4)_2SO_4 \cdot 6H_2O} \). It gives \( \mathrm{Fe^{2+}} \), \( \mathrm{NH_4^+} \) and \( \mathrm{SO_4^{2-}} \) ions.

Step 3: Complex:
A complex keeps its identity in solution. The central metal ion stays bound to its ligands by coordinate bonds and does not give the ion tests of its parts.
Example: \( \mathrm{K_4[Fe(CN)_6]} \) gives \( \mathrm{K^+} \) and \( \mathrm{[Fe(CN)_6]^{4-}} \) ions, but no free \( \mathrm{Fe^{2+}} \) or \( \mathrm{CN^-} \).

Final Answer:
A double salt dissociates fully into simple ions in water, but a complex keeps its complex ion intact.