A lesson in phenomenological chemistry

By Dirk Rohde, March 2013

Polarities collide and form something completely different and new – that is how we might sum up the fields of teaching in class 10 which also resonate with the central questions of this age group. In the chemistry main lesson we deal with that from the perspective of the contrasting pairs of bases and acids as well as the salts they produce.

© Lorenzo Ravagli

Winter. A profound peace holds sway in nature, it is cold, snow falls and gently covers the earth. What season could be better suited to the salts? Their precipitation out of the solution, the creation of beautiful crystal forms just like the ice outside. It is almost as if we are fetching the events of the season into the laboratory when in a cleverly lit round-bottomed flask the sparkling crystals form in a transparent solution and slowly sink to the bottom. Such phenomena should be observed quietly and with concentration, with the greatest possible open-mindedness and detachment, sometimes even with wonder and being inwardly touched if experiments display unexpected and/or beautiful characteristics. Then an inner connection is established with the phenomenon which has a solid foundation. In this context the experiments must be so well chosen, ordered and carried out that they complement and illuminate one another. All observations must be as precise as possible so that causal connections can be derived from them. 

Treating such a subject in main lesson offers many inestimable benefits: its concentration in a few weeks means that the thematic focus can be coordinated with the season. The phenomena can be appreciated as such in a lesson and then left to lie until the next morning, when the underlying causalities can be clarified with an understanding which has matured as a result. There is enough “space” for precise recording. Individual examples can be used to explore the whole subject in every conceivable breadth and depth. And all the explanations can be developed genetically. Which in this context is to say: in the same way as the cognitive process developed in the course of human history; it is therefore often also in line with the cognitive development of the pupils.

Table salt with its enormous importance for human beings takes a very prominent place in the salt main lesson. Every pupil is familiar with it and it provides every pupil with a way into the lessons. From this point the salt concept can easily be extended by investigating the solubility and crystallisation processes in other salts as well – and indeed in other substances which are then distinguished from salts in the course of the main lesson. The pupils can experiment with growing their own crystals, particularly using coloured salts such as copper sulphate. Calculating the solubility curve can introduce the first mathematical steps and a physiological connection can be established through the swelling, shrinking and preservation of organic substances.

In this way we initially start with salt as a unity before breaking it down with heat into alkaline ash and an acidic gas – often after the previous separation of water of crystallisation. It makes sense to pursue this path via some important bases and acids back to the starting elements, which takes us to the contrasting pair of rusting metal – burning non-metal. From that point we can close the circle again with the production of new salts, giving the content of the main lesson structure both an open and closed form.

In terms of the history of science, we are located in the chemistry of the early nineteenth century. In classes 7 to 9 we approached this phase in leaps and bounds through the previous periods and in the later years we will move on to the important new developments in chemistry today. Even without going into the details, we can easily find the associated main lesson structure from what has gone before because the underlying principles are the same.

Writing formulas is therefore often not introduced until class 11. They are not required for a causal understanding of the phenomena, after all, they are not the cause but a consequence of the observation of a sequence of reactions. In preparation we use word equations in the preceding years and address qualitative aspects which occur in that context. We might touch on the first electrochemical experiments in class 10 and begin to discuss individual terms such as “ion” or introduce the first formulas such as “H2O”. But the complex discussion of the “element” will only take place thereafter together with the concept of the atom, radioactivity in physics and cytology in biology; in short, when the question about the smallest meaningful unit crops up. As a result the pupils can approach all the resulting abbreviations (such as the way to write chemical formulas) and hypotheses (such as the structure of the atom) with a more independent and thus freer understanding. There should always be the greatest possible emphasis on pupils experimenting and a practical approach. In class 10 for example: what exactly does road salt do and how is the optimum determined experimentally? Or: why do we have to eat table salt, what happens to it in us and how can we find that out?

The pupils can often establish a much more intensive relationship with such topics than with abstractions. But once they have that solid foundation, they can acquire the abstractions much faster and more easily. As paradoxical as it might sound, premature abstraction in middle school – based on lifeless processes, stone by stone – does not lead to a better understanding in upper school but has the tendency to prevent it. Learning and understanding are organic processes which develop in a living way. This idea is now beginning generally to gain ground. Chemistry teaching in Waldorf schools is seeking to make a contribution to that.

About the author: Dr. Dirk Rohde is a chemistry teacher at the Marburg Free Waldorf School


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