Question

What happens when (give equation):
i) Copper sulphate is heated upto 230 temperature?
ii) Copper sulphate reacts with ammonium hydroxide?
iii) Silver nitrate reacts with hydrochloric acid
iv) Mercuric chloride reacts with potassium iodide?

Answer 1

Hint: (i) When hydrated copper sulphate is heated, it loses water of hydration.
(ii) Copper ions have a tendency of complex formation. Ammonia acts as a ligand in coordination compounds.
(iii) In double displacement reactions, usually a precipitate is obtained.
(iv) In double displacement reaction, cations and anions are exchanged between two compounds.

Complete step by step answer:
When copper sulphate is heated upto 230 temperature, it loses a molecule of water to form anhydrous copper sulphate.
\[{\text{CuS}}{{\text{O}}_4}{\text{.}}{{\text{H}}_2}{\text{O }}\xrightarrow{{230}}{\text{ CuS}}{{\text{O}}_4}{\text{ + }}{{\text{H}}_2}{\text{O}}\]
Before heating, copper sulphate is present in the form of monohydrate. After heating to 230, anhydrous copper sulphate is obtained. Number of water molecules present in monohydrate and anhydrous copper sulfate is 1 and 0 respectively.

When copper sulphate reacts with ammonium hydroxide, it forms a copper complex in which the complex cation has Cu(II) ion surrounded by four ammonia ligands.
\[{\text{CuS}}{{\text{O}}_4}{\text{ + 4 N}}{{\text{H}}_4}{\text{OH }} \to {\text{ }}\left[ {{\text{Cu}}{{\left( {{\text{N}}{{\text{H}}_3}} \right)}_4}} \right]{\text{S}}{{\text{O}}_4}{\text{ + 4 }}{{\text{H}}_2}{\text{O}}\]

Here, there is no change in the oxidation number of any species. Hence, this is not a redox reaction. It is a complex formation reaction as a complex compound is obtained in this reaction.

When silver nitrate reacts with hydrochloric acid, white precipitate of silver chloride is obtained. The byproduct is nitric acid.
\[{\text{AgN}}{{\text{O}}_3}{\text{ + HCl }} \to {\text{ AgCl}} \downarrow {\text{ + HN}}{{\text{O}}_3}\]

Here, there is no change in the oxidation number of any species. Hence, this is not a redox reaction. It is a precipitation reaction as a precipitate of silver chloride is obtained.

Mercuric chloride reacts with potassium iodide to form mercuric iodide and potassium chloride
\[{\text{HgC}}{{\text{l}}_2}{\text{ + 2 KI }} \to {\text{ Hg}}{{\text{I}}_2}{\text{ + 2 KCl}}\]

Here, there is no change in the oxidation number of any species. Hence, this is not a redox reaction. It is an example of double displacement reaction.

Note:
Some metal salts, when heated, readily lose water of hydration.
In complexation reaction, transition metal ions combine with ligands to form coordination compounds.
In double displacement reaction, two compounds exchange cations or anions with each other and form two new compounds. A double displacement reaction can be represented by the following general reaction
\[{\text{AB + CD }} \to {\text{ AD + CB}}\]