Copper(II) ions reacting with aqueous ammonia produce which result?

• A. Blue solution forms.
• B. Light blue precipitate; soluble in excess: dark blue solution.
• C. No precipitate forms.
• D. White precipitate forms.

Answer: (B)

When copper(II) ions meet aqueous ammonia, they first form a light blue precipitate of copper(II) hydroxide, Cu(OH)2, which is insoluble in water. If you add excess ammonia, this solid dissolves because ammonia coordinates to the copper ion, creating the deep blue copper–ammonia complex [Cu(NH3)4(H2O)2]2+. So you see a light blue precipitate forming, which then dissolves in excess to give a dark blue solution. The other options don’t fit because you do get a precipitate (not no precipitate) and that precipitate is not white, and there is not an immediate blue solution without the precipitate forming first.