Copper–Oxygen Compounds and Their Reactivity: An Eye-Guided Undergraduate Experiment

The chemistry of CuI and CuII is rich, and these oxidation states can be converted into each other by using quite mild or more strong oxidizing or reducing agents, depending on the starting materials and reaction conditions. Thus, this work describes an easy way to obtain yellow copper(I) oxide from copper(II) sulfate, using hydroxylamine hydrochloride as a reductant. In addition, the aqueous chemistry of CuII is very abundant, and in basic media, it perfectly exemplifies the chemistry of any transition metal having amphoteric hydroxides. For this purpose, copper(II) hydroxide is prepared from copper(II) sulfate by addition of basic medium. The insoluble amphoteric hydroxide reacts again with a solution of sodium hydroxide to form the corresponding water-soluble sodium tetrahydroxocuprate(II). Finally, an experiment is carried out to demonstrate the instability of CuI in aqueous acid medium, which disproportionates to form Cu0 and the corresponding water-soluble copper(II) salt. This set of experiments has been designed to be performed in a single 3–4 h laboratory session, and it has been tested several times with second-year undergraduate chemistry students at the University of Santiago de Compostela (Spain).