We present a critical discussion of how chemistry textbooks treat the electrolysis of water and aqueous salt solutions, based on a survey of general chemistry textbooks in English and Korean at secondary and tertiary levels, also informed by the historical background of 19th-century debates. English-language textbooks present various and contradictory accounts of the electrolysis of water; a key point of disagreement is whether hydrogen and oxygen gases originate from pre-existing H⁺ and OH⁻ ions, or from the direct reduction and oxidation of H₂O molecules. School textbooks in South Korea all present the same account, with no indication of alternative views. A vast majority of all texts ignore the possibility that H₂ and O₂ may result from secondary reactions, which was a standard view in the late 19th century following the works of Daniell and Miller. Concerning the electrolysis of aqueous salt solutions, all texts give oversimplified views of competing reactions based on standard reduction/oxidation potentials. It is understandable that textbooks try to present sufficiently simple pictures that students at each level can handle; however, this should not be done in a way that shuts down questions. We recommend that students should be made aware that textbook accounts are only models, and encouraged to extend their learning beyond the models. The plausibility of our recommendations is shown in a pilot study we conducted with secondary school students in South Korea.

The four representative models that define oxidation–reduction reactions are often used differently in different situations or contexts in chemistry textbooks. Although integrated models have been suggested to overcome the confusion caused by this, they have not been successful. We therefore aim to interpret the causes for difficulties in the attempted integration of the various epistemological perspectives. The four key models, namely, the oxygen, hydrogen, electron, and oxidation state (or number) models, focus on the movement of matter. We, however, suggest the use of the Goodstein method, where the relative changes in the electronegativity orders in redox reactions should be employed rather than the properties of the reactants or products themselves. This requires a change of viewpoint from matter to process. We also suggest that the confusion of classifying redox reactions may occur from the viewpoint of matter. Therefore, new interpretations of redox reactions based on the relationship between reactants and products are suggested, considering the process viewpoint as a valuable criterion. While many researchers have tried to solve this problem by suggesting new models to classify redox reactions, we instead suggest a novel interpretation of the various redox models.

Water electrolysis is used to teach important and fundamental concepts in chemistry. In practical water electrolysis experiments, it is difficult to achieve the ideal 2:1 ratio of hydrogen to oxygen. This work demonstrates an experimental setup comprising multiple water electrolysis cells connected in series to simultaneously visualize the effects of various electrode materials and electrolytes on water electrolysis. The volumes of oxygen were lower when using stainless steel and graphite anodes, which corrode in the electrolytes containing SO4 2– and NO3 – anions, compared to those in the presence of the noncorroding Pt electrode. In addition, the volumes of hydrogen in the presence of NO3 – anions, which are catalytically reduced on the cathodes of stainless steel and graphite, were remarkably lower than those obtained with the noncatalyzing Pt cathode. These phenomena are attributed to side reactions which consume portions of the electrons intended for water electrolysis. This demonstration can help students to realize that the experimental results of water electrolysis should be carefully interpreted as they may include a contribution from electrode side reactions.