MCQ
When ammonia is added to a cupric salt solution, the deep blue colour is observed it is due to the formation of 
  • A
    ${\left[ {Cu{{\left( {OH} \right)}_4}} \right]^{2 - }}$
  • ${\left[ {Cu{{\left( {N{H_3}} \right)}_4}} \right]^{2 + }}$
  • C
    ${\left[ {Cu{{\left( {{H_2}O} \right)}_2}{{\left( {N{H_3}} \right)}_2}} \right]^{2 + }}$
  • D
    ${\left[ {Cu{{\left( {{H_2}O} \right)}_4}} \right]^{2 + }}$

Answer

Correct option: B.
${\left[ {Cu{{\left( {N{H_3}} \right)}_4}} \right]^{2 + }}$
b
Since, the ammonia has stonger ligand bonds than water with $Cu ^{2+}$. Hence, it can then forms a blue coloured solution of complex salt.

$Cu \left( SO _4\right) \cdot 5 H _2 O +4 NH _4 OH \rightarrow Cu \left( NH _3\right)_4 SO _4 \cdot H _2 O +8 H _2 O$

$Cu ^{2+}+4 NH _3 \rightarrow\left[ Cu \left( NH _3\right)_4\right]^{2+}$

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