The etching solution eventually becomes saturated with copper (II) oxide, which starts precipitating out of the solution as a blue-green solid. It takes a while to get there, though; depending on ...

Continue adding copper(II) oxide powder until it is in excess and remains as a black powder in the solution. 4. Fold a piece of filter paper and put it into a filter funnel. Fit the filter funnel ...

Also, although there is no gas produced, there is a chemical reaction taking place as the solution changes from colourless to a pale blue, you should also notice that the copper(II) oxide ...