Plasma-liquid interactions are becoming increasingly interesting because of their main characteristics such as non-Faraday non-equilibrium behavior as well as electron-driven reactions, and therefore can have powerful implications for several promising applications. Understanding the reaction mechanisms triggered at the interface between plasma and liquid is made difficult by short time scales and spatial irregularities. Here we investigate a plasma-ethanol system that is generally relevant to broaden our understanding of the interaction of plasma on the surface of a liquid. This plasma electrochemical approach has been successfully used to synthesize a number of metal oxide nanoparticles and quantum dots (QDs). While nanoparticles and QDs can put an end to this process, they can also be viewed as “chemical probes” that facilitate understanding of the underlying chemical reactions and the precursor reactions. We therefore investigated plasma-ethanol interactions during the synthesis of CuO QDs. The colloid was characterized by Fourier transform infrared spectroscopy, UV spectroscopy, nuclear magnetic resonance spectroscopy and gas chromatography-mass spectrometry. Measurements of pH and other trace products were also carried out. The analysis shows the acidolysis of the ethanol electrolyte, during which hydrogen peroxide was found after the plasma process. Half-quantification of Cu ions was carried out to confirm the anodic dissolution of the Cu metal foil. Therefore, a detailed set of reactions is proposed and discussed at length. The material characterization was based on transmission electron microscopy and X-ray photoelectron spectroscopy, which provided important and additional information to confirm chemical reaction pathways.