The backstory of balancing equations

Yasmin Jayathirtha

I was once asked, “How do you teach students to balance equations? The teachers are finding it very difficult.” As I gave a few suggestions, the reason for the difficulty emerged – these students are in the 6th or 7th class, they have not yet learnt atomic structure, bonding, or valency. This means that they do not know why the formulae of substances are what they are. They have to look them up. Why then are they being asked to balance equations? If there has to be chemistry in these classes, surely it can be descriptive chemistry such as teaching the idea of chemical change, outlining the questions that chemists asked, the simple tests that are used to identify common substances, the chemistry of air, water, metals – familiar substances and familiar processes like evaporation, dissolving, corrosion, etc… but of course, this means doing simple experiments and observing changes. At this stage, science has to be integrated.

exp Most textbooks that I have consulted have covered the ideas of atomic structure, bonding, formulae, and the mole, before coming to the concept of a balanced equation, usually by the 9th class. It just doesn’t make sense to balance equations before learning these concepts. Equations there are, but they are word equations, just describing the reactions that occur. Many subjects have hierarchies, and taken out of context, a concept will just become a matter of rule to follow, rather than adding to the understanding of the subject. No wonder, students find chemistry difficult, being unable to relate what they have learnt to the world they know and being asked to memorize rather complicated formulae and do algebra!

How does one introduce the idea of a balanced equation qualitatively? This is a paradox, since the idea of equations is the start of quantitative chemistry and is linked to the relationship between numbers of particles and their mass – the link between the sub-microscopic world of atoms and the macroscopic world of measurement. Should one even try? I am torn between ‘shouldn’t be done’ and ‘poor kids, how can it be made a little more intelligible?’

Start with reactions – how do we know a reaction has occurred? We can demonstrate various reactions. Add a drop of hydrochloric acid to a piece of magnesium or zinc. Has a change occurred? What do we observe? Bubbles tell us that a gas has formed. After a while, the metal disappears – reaction has taken place. Allow the reacted mixture to dry. There will be white solid substance left behind. So we can write the reaction as;

The author works with Centre for Learning, Bengaluru. She can be reached at yasmin.cfl@gmail.com.

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