When \(6 M\) ammonia is added gradually to aqueous copper(II) nitrate, a white precipitate forms. The precipitate dissolves as more \(6 M\) ammonia is added. Write balanced equations to explain these observations. [Hint: \(\mathrm{Cu}^{2+}\) reacts with \(\mathrm{NH}_{3}\) to form \(\left.\mathrm{Cu}\left(\mathrm{NH}_{3}\right)_{4}{ }^{2+} .\right]\)

: Initially, when ammonia is added to copper(II) nitrate, a white precipitate forms. This is most likely due to the reaction between the copper(II) ions and hydroxide ions (formed from the reaction between ammonia and water) to form copper(II) hydroxide, which is a white precipitate. The reactions involved are: \[NH_3 + H_2O \rightarrow NH_4^+ + OH^-\] \[Cu^{2+} + 2OH^- \rightarrow Cu(OH)_2\] Combined, we can write the balanced equation for the formation of copper(II) hydroxide precipitate as: \[Cu^{2+} + 2NH_3 + 2H_2O \rightarrow Cu(OH)_2 + 2NH_4^+\]

: As more ammonia is added, the precipitate dissolves. This can be explained by the complexation of copper(II) ions with excess ammonia to form the tetraamminecopper(II) complex ion as hinted in the problem statement. The balanced equation for this reaction is: \[Cu(OH)_2 + 4NH_3 \rightarrow [Cu(NH_3)_4]^{2+} + 2OH^-\] So, when more ammonia is added to the solution, copper(II) hydroxide dissolves to form the tetraamminecopper(II) complex ion which remains in solution. In conclusion, the exercise requires us to write balanced equations for the formation and dissolution of a white precipitate upon the gradual addition of ammonia to aqueous copper(II) nitrate solution. Initially, copper(II) hydroxide precipitates are formed due to the reaction between copper(II) ions and hydroxide ions. As more ammonia is added, copper(II) hydroxide dissolves to form the soluble tetraamminecopper(II) complex ion.