When you gently pour diluted hydrochloric acid into a beaker with a small amount of copper oxide while stirring, the solution turns blue-green as the copper oxide dissolves. The reaction's production of_____________ is what gives the solution its blue-green hue.

Add diluted water to a little amount of copper oxide in a beaker. The colour of the solution turns blue-green as the copper oxide dissolves when hydrochloric acid is added gradually while stirring. The reaction results in the creation of copper(II) chloride, which gives the solution its blue-green hue.

This is an example of a double displacement reaction.