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Q.
On adding excess of $NH_{4}OH$ to copper sulphate solution
NTA AbhyasNTA Abhyas 2020The d-and f-Block Elements
Solution:
With ammonium solution, $CuSO _{4}$ forms a stable blue complex. First it
forms a precipitate of $Cu ( OH )_{2}$ which dissolves in excess of ammonia
solution forming a deep blue coloured complex.
$\mathrm{CuSO}_4+2 \mathrm{NH}_4 \mathrm{OH} \rightarrow \mathrm{Cu}(\mathrm{OH})_2+\left(\mathrm{NH}_4\right)_2 \mathrm{SO}_4 $
$
\mathrm{Cu}(\mathrm{OH})_2+2 \mathrm{NH}_4 \mathrm{OH}+\left(\mathrm{NH}_4\right)_2 \mathrm{SO}_4 \rightarrow \mathrm{Cu}\left(\mathrm{NH}_3\right)_4 \mathrm{SO}_4+4 \mathrm{H}_2 \mathrm{O}
$
Tetraamminecupricsulphate