Question

What happens when excess of ammonia is added to $CuS{O}_4$ solution ?

• A. $\left[Cu\right(N{H}_3{)}_{5}S{O}_4]$
• B. $\left[Cu\right(N{H}_3{)}_4]S{O}_4$
• C. $\left[Cu\right(N{H}_3{)}_{3}S{O}_4]$
• D. $\left[Cu\right(N{H}_3{)}_6]S{O}_4$

Answer 1

Answer: (B)

$\left[Cu\right(N{H}_3{)}_4]S{O}_4$

When ammonia solution is added to solution of $C{u}^{2+}$, a blue precipitate of a basic copper sulphate is obtained, which is soluble on excess reagent giving deep-blue colouration of tetramminecopper (II) sulphate.

$2C{u}^{2+}+S{O}_4^{2-}+2N{H}_3+2H_{2}O\to Cu(OH{)}_2.CuS{O}_4\downarrow +2N{H}_4^{+}$

Blue ppt

$Cu(OH{)}_2.CuS{O}_4\downarrow +8N{H}_3\to 2[Cu(N{H}_3{)}_4{]}^{2+}+S{O}_4^{2+}+2O{H}^{-}$

Deep-blue coloration