Question

A solution of ferric chloride in water is acidic to litmus due to:

• A. hydrolysis
• B. decomposition
• C. electrolysis
• D. condensation

Answer 1

Answer: (A)

When ferric chloride is dissolved in water the solution becomes acidic as a result of hydrolysis. The chemical reaction, in words and formulae are: Basically, ferric chloride in water solution ionizes to iron (ferric) and chloride ions, whilst the water ionizes to hydrogen and hydroxide ions;

$FeC{l}_3\to F{e}^{3+}+3C{l}^{-}$

$H_{2}O\to H^{+}+O{H}^{-}$

The ferric ions will partially combine with the hydrogen and hydroxide ions to form the ferric hydroxide, a compound that is only slightly soluble and precipitates from solution as a brown solid.

$F{e}^{3+}+3O{H}^{-}\to Fe(OH{)}_3$

This precipitation can be regarded as removing hydroxyl ions from the solution, leaving a relative excess of hydrogen ions and it is this excess of hydrogen ions that makes the solution acidic.

So the answer is $A$.