A rare-earth barium copper oxide (REBCO) is now being used by an Oxfordshire-based company for its superconducting properties ...

Stop adding the copper oxide when it's in excess - in other words when the black powder doesn't disappear anymore. This means there is no remaining sulfuric acid to react. The next step is ...

Copper carbonate is green and copper oxide is black. You can see a colour change from green to black during the reaction. The carbon dioxide produced can be detected using limewater, which turns ...