question_answer

Write equations to represent the following observations: When NaOH is added to aqueous \[CuS{{O}_{4}}\] solution, a pale blue precipitate is formed. On adding aqueous \[N{{H}_{3}}\] solution, the precipitate dissolves to give a deep blue solution. If the solution is made acidic with dilute \[HN{{O}_{3}},\] the colour is converted back to pale blue solution.

Answer:

\[C{{u}^{2+}}(aq)+2\,O{{H}^{-}}\,(aq)\xrightarrow{\,}\,\underset{\text{pale}\,\,\text{blue}\,\,\text{ppt}\text{.}}{\mathop{Cu{{(OH)}_{2}}(s)}}\,\] \[Cu{{(OH)}_{2}}\,(s)+4N{{H}_{3}}\,(aq)\xrightarrow{{}}\]\[\underset{\text{deep}\,\,\text{blue}}{\mathop{{{[Cu{{(N{{H}_{3}})}_{4}}]}^{2+}}}}\,\,(aq)+2O{{H}^{-}}\,(aq)\] \[{{[Cu{{(N{{H}_{3}})}_{4}}]}^{2+}}\,(aq)+\underset{\text{(acidic)}}{\mathop{4\,{{H}_{3}}{{O}^{+}}}}\,\xrightarrow{\,}\]\[\underset{\text{pale}\,\,\text{blue}\,\,\text{solution}}{\mathop{{{[Cu{{(OH)}_{4}}]}^{2+}}}}\,+4\,NH_{4}^{+}\ (aq)\]