Question

When aqueous solutions of potassium fluoride is added to the blue coloured aqueous $CuSO_{4}$solutions, a green precipitate is formed. This observations can be explained as follows.

• A. On adding KF, $H_{2}O$being weak filed ligand is replaced by $F^{-}$ions forming $\lbrack CuF_{4}\rbrack^{2 -}$which is green in colour.
• B. Potassium is coordinated to $\lbrack Cu(H_{2}O)_{4}\rbrack^{2 +}$ion present in $CuSO_{4}$and gives green colour.
• C. On adding KF, $Cu^{2 +}$are replaced by $K^{+}$forming a green complex.
• D. Blue colour of $CuSO_{4}$and yellow colour of KI form green colour on mixing.

Answer 1

Answer: (A)

On adding KF, $H_{2}O$being weak filed ligand is replaced by $F^{-}$ions forming $\lbrack CuF_{4}\rbrack^{2 -}$which is green in colour.

Answer 2

Aqueous $CuSO_{4}$solutions contains $\lbrack Cu(H_{2}O)_{4}\rbrack^{2 +}$ions which are blue in colour. When aqueous solutions of KF is added, $H_{2}O$being weak filed ligand can be replaced by $F^{-}$ions forming $\lbrack CuF_{4}\rbrack^{2 -}$which is green in colour.

$\lbrack Cu(H_{2}O)_{4}\rbrack^{2 +}\underset{(fromKF)}{+ 4F^{-}} \rightarrow \underset{Green}{\lbrack CuF_{4}\rbrack^{2 -}} + 4H_{2}O$