Solvatochromism of Cupric Chloride and Its Conversion to Copper Oxide

This experiment demonstrates that copper(II) chloride dihydrate (CuCl2·2H2O) in different solvents (acetone, isopropyl alcohol, or water) displays divergent colors and visible-near IR spectra. Both the reactions of these solutions with 2 equiv of sodium hydroxide (NaOH) and the direct solid-state reaction of CuCl2·2H2O with 2NaOH using a mortar and pestle give copper(II) oxide (CuO). Undergraduate students learn the following: (1) d–d electronic transitions in a transition metal complex; (2) effects of solvent polarity changes on the electronic ground and excited state of Cu2+ ions as well as color differences; (3) direct solid-state reaction as a green synthetic method; (4) gradual formation of CuO from solution reactions of CuCl2·2H2O with 2 equiv of NaOH; (5) characterization of chemical compounds in solutions by visible-near IR spectroscopy and solid products by IR and powder X-ray diffraction (PXRD). This experiment is suitable as a junior-level inorganic chemistry experiment.