Oxide copper, so it displaces copper (II) oxide to form zinc oxide: Apart from metals, hydrogen can also displace metal oxides to form hydrogen oxide, also known as water: Since metals that are reactive form oxides that are stable, some metal oxides must be electrolyzed to be reduced. This includes sodium oxide, potassium oxide, calcium oxide, magnesium oxide, and aluminium oxide. The oxides must be molten before immersing graphite electrodes in them: Oxides typically react with acids or bases, sometimes both. Those reacting only with acids are labeled basic oxides. Those reacting only by bases are called "acidic oxides". Oxides that
Copper(II) oxide from the solids. These complexes are decomposed with steam to give CuO. It can be formed by heating copper in air at around 300 – 800°C: For laboratory uses, pure copper(II) oxide is better prepared by heating copper(II) nitrate, copper(II) hydroxide or copper(II) carbonate: Copper(II) oxide dissolves in mineral acids such as hydrochloric acid, sulfuric acid or nitric acid to give the corresponding copper(II) salts: It reacts with concentrated alkali to form the corresponding cuprate salts: It can also be reduced to copper metal using hydrogen, carbon monoxide, or carbon: When cupric oxide is substituted for iron oxide in thermite