Visualization Experiment of Ion Migration in Electrolytic Cell Based on Natural Indicator

Visible color changes in a real electrolysis experiment can help to develop students’ concepts of the electrolysis process, such as ion migration. In this paper, a copper sheet was used as the cathode, an iron sheet as the anode, and a pink agar gel soaked with sodium sulfate solution and Chinese goldthread (Coptis chinensis Franch.) fruit extract (CGFE) was used as the electrolyte. When electrolysis occurred, green and gray-purple colors were observed around the cathode and anode, respectively, in the electrolytic cell, with migration of green and gray-purple toward the anode and cathode, respectively, as electrolysis proceeded. The generation of green and gray-purple regions was due to the reaction of OH^– produced at the cathode and Fe²⁺ produced at the anode with the anthocyanins of CGFE, as well as the migration of OH^– and Fe²⁺ toward the anode and cathode, respectively, under the action of the electric field. Thus, the ion migration that occurred at the submicroscopic level was visualized through macroscopic color migration in experiments. Other macroscopic phenomena during electrolysis such as gas production and precipitation at the meeting of green and gray-purple regions was related to the mechanism of electrode and ion reactions which could be used as experimental support for the understanding of ion migration in the electrolytic cell, as well as for the development of other related chemical concepts.