Question

A solution of ferric chloride in water is acidic to litmus due to:
A.Hydrolysis
B.Decomposition
C.Electrolysis
D.Condensation

Answer 1

Hint: Ferric chloride is a dark color crystal where the oxidation state of iron is+3. Its chemical formula is $FeC{l_3}$ and is also known as Molysite. Basically, ferric chloride in water ionizes to iron i.e. ferric and chloride ions and the water ionizes to hydrogen and hydroxide ions.

Complete step by step answer:

Ferric chloride or Molysite is an iron coordination entity which functions as a Lewis acid. It can be prepared by reacting metallic iron with dichloride. The equation is as shown:
 $2Fe + 2C{l_2} \to 2FeC{l_3}$
Now, when ferric chloride is dissolved in water, the solution becomes acidic due to hydrolysis. Moreover, the ferric chloride in water solution ionizes to iron and chloride ions whereas water ionizes to hydrogen and hydroxide ions. The equations are as shown:
 $FeC{l_3} \to F{e^{ + 3}} + 3C{l^ - }$
 ${H_2}O \to {H^ + } + O{H^ - }$
Further, the ferric ions will partially combine with the hydrogen and hydroxide ions to form ferric hydroxide. It is a compound that is slightly soluble and precipitates as a brown solid. The reaction is as shown:
 $F{e^{ + 3}} + 3O{H^ - } \to Fe{(OH)_3}$
So, this precipitation removes the hydroxyl ions from the solution leaving a relative excess of hydrogen ions and this excess of hydrogen ions makes the solution acidic.

Hence, option A is correct.

Note: Ferric chloride is used as a drying agent in some reactions in its anhydrous form. It is also used in organic synthesis as a catalyst. Moreover, a ferric chloride test is used to determine the presence or absence of phenol in a given sample. The compounds such as enols, oximes, hydroxamic acids give positive results.