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  • Writer's pictureKaty Duncan

Electrolysis and Education: Learning Models not Facts

Katy Duncan is a PhD student in the Department of History and Philosophy of Science at the University of Cambridge. In this piece, Katy explores the seemingly contradictory ways we teach the electrolysis of water to teenagers. In embracing pluralist explanations and favouring 'model-teaching’, she argues that we can better foster the essential curiosity in students that is necessary for becoming a scientist. 

Growing up, I always thought chemistry was the most suspicious science. In most of my secondary school chemistry classes I had the niggling feeling like I was being lied to; that what I was being taught was just some pre-packaged, neat and tidy version of the truth. What was written in my textbooks, I thought, wasn’t what actually happened when we did our experiments in the laboratory. Frustrated, I decided to stop studying chemistry at the age of 16, instead believing my answers about the universe might be resolved by pursuing physics (spoiler: they were not).  

A decade later I was working as a researcher for Hasok Chang, and we were investigating how modern school textbooks explained the electrolysis of water – the process of using electricity to split water into its component parts of hydrogen and oxygen – in order to compare it to historical accounts.

Image showing the electrolysis of water

Figure 1 A simple experimental set up for the demonstration of the electrolysis of water. (Image from Wikimedia Commons.)

To my horror, I found a medley of explanations and equations. At each level of education there were significant disagreements in the treatment of electrolysis: it was not the case of the common progression of accounts in which the teachers might say to the students, ‘‘what we taught you last year was wrong.’’ Crucially, there were significant disagreements about how the hydrogen and oxygen gases produced in the electrolysis of water are formed, as can be seen in Table 1. Are there ‘pre-existing ions’ in water, or is the whole-H2O molecule electrolysed at the electrode? The textbooks also presented wildly different microphysical pictures of what was going on at the atomic level, regardless of educational level. Were these textbooks seriously proposing different physical mechanisms, or were they more concerned with equation balancing for easy-to-mark examinations? In many cases it was unclear whether the reactions implied by the equations were proposed as real, and the plausibility or probability of those reactions were not discussed.

Table 1: The different physical mechanisms given by textbooks concerning how hydrogen and oxygen are produced in the electrolysis of water. (-) and (+) indicate the reaction that occurs at the cathode and anode respectively

Gritting my teeth, we decided to dig a little deeper. We compared our work with the research done by our South Korean co-authors Seoung-Hey Paik and Kihyang Kim on their secondary-school textbooks. South Korea is a high-performing nation with a very different linguistic, cultural and institutional setting from European-origin societies, and compared with the English education system, the Ministry of Education in South Korea exerts a strong control over the national curriculum and the approval of textbooks. 

They found that all of the Korean textbooks gave Type 2 accounts: that H2O molecules are directly decomposed at the electrodes. Though consistency might be useful, isn’t it disturbing? All the other options are clearly considered as possibilities in respectable English-language textbooks. And it soon became clear to us that Type 2 wasn’t necessarily the best possible of the four either. As our paper details more thoroughly, even when we go beyond equation balancing and assess the microphysical pictures given by some textbooks, we are none the wiser which of the above options is the best. All Types 1 to 4 face difficulties the more they are prodded, and it becomes increasingly challenging to give a neat story at the higher level of discussion. This could be why we found that fewer higher-level texts even chose to engage with the subject.

What are we to make of this? What happens when a student encounters differing stories when going from one level of study to the next, or by changing schools? Or for Korean students who may go on to university and encounter English-language textbooks that give a different account? Is it better to be consistent in giving an inadequate answer, or to disseminate mutually inconsistent stories, each presented as the right answer? Neither is a desirable option. 

There is also a troubling practical question to examine: any classroom teacher or student doing electrolysis experiments will tell you that you need to add a small quantity of electrolyte (e.g. a salt, acid, or base) to water in order for decomposition to occur at an observable rate. But why is this? And how can we understand the electrolysis of water, as given in the equations above, without accounting for the necessary addition of this electrolyte? Textbook explanations about this are simply inadequate.

Figure 2 John Frederic Daniell, inventor of the Daniell cell (Image from Wikimedia Commons) 

The history of science might offer us a hand. John Frederic Daniell (1790–1845) made an important discovery in 1840: that the final products of electrolysis were not necessarily the actual components of the electrolyte itself. This view was developed by William Allen Miller (1817–1870). So, if you were to electrolyse a solution of sodium sulphate in water, Miller argued there was a two-step process, and that hydrogen and oxygen are secondary, not primary, products of the reaction:

Figure 3 William Allen Miller, Daniell’s successor. (Image from Wikimedia Commons)

Miller (1867, pp.524-252) concluded: ‘‘it is manifest that water itself is not an electrolyte, but it is enabled to convey the current if it contain only faint traces of saline matter.’’ This ‘‘Daniell–Miller view’’ of the electrolysis of water and aqueous solutions assigned a precise role to the added electrolyte in the electrolysis of water through the idea of primary and secondary products. It also makes it clear that the electrolysis of water should really be taught as the electrolysis of an aqueous solution, just at the low-concentration limit, which nearly all modern textbooks do not adequately explain. Here, models from history provide explanations for questions that today’s textbooks attempt to gloss over. Perhaps the theories of the past shouldn’t be left to gather dust.

But all these insights are meaningless without application! Notwithstanding, we carried out a pilot study with 10th grade students at the Sejong Academy of Science and Arts, a secondary school for gifted students in South Korea. 23 students volunteered to take part. The study was designed to allow students to encounter situations where their experimental results did not agree with the simplified accounts given in their textbooks. Afterwards we conducted a brief survey asking the students to give us their view on the relation between these experimental outcomes and their textbooks. When asked about the relation between their experimental results and what they had learned from their textbooks, a clear majority (78%) responded that they thought textbooks articulated simple principles or regularities discernible within complex natural phenomena, expressing an appreciation of the value of the textbook account despite the discrepancy with observations. More interestingly, when then asked about their attitudes towards the study, though nearly two-thirds of students said that they experienced cognitive dissonance, all of these students also said that these experiments were more interesting to them than the standard electrolysis experiments. In free-form answers describing their experience, many of these students then gave indications of sophisticated thinking beyond their prescribed level, including how to handle discrepancies between theory and experiment and the process of refining a theory. All of the students agreed that these experiments demonstrated to them that it was necessary to consider many variables – more than their textbooks indicated – in order to correctly predict the results of electrolysis. 

At least with these highly motivated and able students there are clear benefits to offering them opportunities to explore the complexity of phenomena, even if this should be in addition to the prescribed syllabus. We found that it generates a much greater potential for learning compared to the usual experiments in which students learn to produce the results dictated by simplified textbook accounts. 

So how should we teach the electrolysis of water? Our conclusion was that students should be taught what it is to be a chemist, rather than be pedants of particular models taught as truths. Models are thinking tools with certain scopes and limitations, and multiple models can and should be explored to explain a given phenomenon. Of course, teaching involves making choices about what is teachable and how to teach it, but this strikes deep parallels with how chemists of the past and present develop different models to explain the world. The more we dig into any phenomena the more caveats and ad-hoc adjustments we find ourselves making, and a physicist and a chemist will develop different models to explain a phenomenon because they value different things. There is no singular linear set of explanations that build upon each other, becoming more complex and closer to unveiling “the truth” about a phenomenon: there is no master equation. The model used reflects the values of the modeller, just like simplifications for education, too, reflect the educator’s values about what is most important to teach.

Whilst the researcher may be familiar with model-making and exploring the array of explanations out there, it is precisely these aspects of the scientific endeavour that have been evicted from most educational settings. It is perfectly understandable that textbooks offer simplified accounts, but they are models with theoretical insights, not exact descriptions of nature. Whilst textbooks are guilty of many things, prioritising equation balancing derived from highly improbable or outright fictitious physical mechanisms over giving students time to explore the models for what they are – models – is particularly criminal. We should avoid teaching these scenarios as “what really happens” in nature, and in doing so, look to make stronger links between the simplification that occurs in education with the model-based research that scientists undertake all the time.

Further, explanations proposed in the past may disappear from modern pedagogy, but this does not necessarily mean they were wrong. As we have seen through the case of the Daniell–Miller view, a forgotten past model can offer useful questions and answers for modern students. The history of science also gives students the opportunity to engage with research questions faced by past scientists, and it may spark a real curiosity of “doing chemistry.”

Lastly, in recognizing textbook accounts as simplified models, more adept and motivated students can engage in creative and critical thinking instead of accepting one explanation as being true. Our pilot study points to clear potential in this direction. Textbooks and teachers should try to move beyond the kind of neat stories that result in shutting down questions that require more sophisticated discussions. Though it is unrealistic to examine all the difficulties in textbooks, all levels of teaching should demonstrate the limits of what the model they use can capture. Recognizing the educational value of questioning the models that are taught can ignite curiosity about unexplained phenomena and foster the sense of scientific inquiry. 

On reflection, the result of being taught models as truths all those years ago was that my sense of inquiry into chemistry was slowly squeezed out of me. If I had been told that what I learnt at every stage was not “the truth” but merely models, who knows, perhaps I would have become a chemist after all. 


  • Cartwright (1983) How the Laws of Physics Lie

  • Chang, Hasok, et al. "Electrolysis: What textbooks don’t tell us." Chemistry Education Research and Practice (2020).

  • Daniell J. F., (1840), Second Letter on the Electrolysis of Secondary Compounds, Philos. Trans. R. Soc. London, 130, 209–224

  • Miller W. A., (1867), Elements of Chemistry: Theoretical and Practical, Part 1. Chemical Physics, 4th edn, London: Longmans, Green, Reader, and Dyer, pp. 524–525.

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