What color precipitate do copper (II) ions produce when reacted with sodium hydroxide solution?

Copper (II) ions react with sodium hydroxide solution to form a blue precipitate of copper(II) hydroxide. This reaction is characteristic of copper ions and is commonly used to identify them in qualitative analysis. The hydroxide ions from the sodium hydroxide combine with the copper(II) ions to form the insoluble copper(II) hydroxide, which appears as a vivid blue solid.

The blue color of the precipitate is due to the presence of copper (Cu^2+) ions, which exhibit characteristic colors in solution and when precipitated. This distinctive coloration can be very helpful in identifying copper(II) in a solution.

In contrast, other metal hydroxides may yield different precipitate colors: for instance, iron(III) forms a reddish-brown precipitate, aluminum typically results in a white precipitate when reacted with sodium hydroxide, and other transition metals may produce green or other colored precipitates. Thus, blue is specifically indicative of copper(II) hydroxide in this reaction.