Question

Aqueous copper sulphate solution (blue in colour) gives:
(i)A green precipitate with aqueous potassium fluoride and
(ii)a bright green solution with aqueous potassium chloride. Explain these experimental results.

Answer 1

Hint: Copper sulphate is a chemical compound composed from the elements copper, sulphur and oxygen. It is used as fungicide and herbicide in agriculture and non agricultural fields. Copper sulphate is blue in aqueous form.

Complete step by step answer:
As we all know that copper sulphate is blue in colour only in aqueous form so after adding copper sulphate in water it forms ${\left[ {Cu{{({H_2}O)}_4}} \right]^{2 + }}$ ion which is the main reason of blue colour of aqueous copper sulphate.
In the reaction (i) when aqueous copper sulphate reacts with aqueous potassium fluoride a green coloured precipitate is formed.
Reaction:
${\left[ {Cu{{({H_2}O)}_4}} \right]^{2 + }} + 4{F^ - } \to {\left[ {Cu{F_4}} \right]^{2 - }} + 4{H_2}O$
Where ${\left[ {Cu{F_4}} \right]^{2 - }}$ is formed as a green precipitate.
In reaction (ii) when aqueous copper sulphate reacts with aqueous potassium chloride a bright green solution is formed.
Reaction:
\[{[Cu{(H2O)_4}]^{2 + }} + 4C{l^ - } \to {[CuC{l_4}]^{2 - }} + 4{H_2}O\]
In this reaction \[{[CuC{l_4}]^{2 - }}\] is the bright green solution.
As we can see that in both the reaction water is replaced by the chloride and fluoride ions, this happens because water is a weak field ligand whereas chloride and fluoride ions are strong field ligands.

Note: Copper sulphate can be dangerous if not handled carefully. It causes severe eye irritation. Eating copper sulphate in large amounts can cause vomiting and damage to body tissues, blood cells, liver and kidneys. Sometimes this results in death also.