A tour around Johnstone’s Triangle

In a small laboratory off the M25, is a man named Bob. And Bob is a genius at designing and completing reactions on a very small scale. Bob is greatly helped by Dr Kay Stephenson, Mary Owen and Emma Warwick.

I was invited to go down to CLEAPPS to see Bob in action, and try out for myself some of the microscale chemistry he has been developing. I was interested to see it because of a general interest in laboratory expriments and how we can expand our repertoire. But I found out a lot more than just smaller versions of laboratory experiments.

Safety and cost considerations first piqued Bob’s interest in microscale. The traditional laboratory Hofmann voltmeter costs about £250, but the microscale version, including ingenious three way taps to syringe out the separated gases costs about £50. Thoughts about how to do a reduction of copper oxide safely led him to use a procedure that avoided traditional problems with explosions. There’s also a very neat version using iron oxide, incorporating the use of a magnet to show that iron forms.

Electrochemical production of leading to subsequent production of iodine and bromine. Copper crystals form on the electrode.
Electrochemical production of chlorine leading to subsequent production of iodine and bromine. Copper crystals form on the electrode.

Bob promised to show me 93 demonstrations in a morning (“scaled back from 94!”) and I worried on my way there that I would have to put on my polite smile after a while. But actually time flew, and as we worked through the (less than 93) experiments, I noticed something very obvious. This isn’t just about safety and cost. It has deep grounding in the scholarship of teaching and learning too.

Cognitive Load

What I remember from the session is not the apparatus, but the chemistry. Practical chemistry is difficult because we have to worry about setting up apparatus and this can act as a distraction to the chemistry involved. However, the minimal and often absence of apparatus meant that we were just doing and observing chemistry. This particularly struck me when we were looking at conductivity measurements, using a simple meter made with carbon fibre rods (from a kite shop). This, along with several other experiments, used an ingenious idea of instruction sheets within polypropylene pockets (Bob has thought a lot about contact angles). The reaction beaker becomes a drop of water, and it is possible to explore some lovely chemistry: pH indicator colours, conductivity, precipitation reactions, producing paramagnetic compounds, all in this way. It’s not all introductory chemistry; we discussed a possible experiment for my third year physical chemists and there is lots to do for a general chemistry first year lab, including a fabulously simple colourimeter.

Designing a universal indicator.
Designing a universal indicator.

Johnstone’s Triangle

One of the reasons chemistry is difficult to learn is because we have multiple ways of representing it. We can describe things as we view them: the macroscopic scale – a white precipitate forms when we precipitate out chloride ions with silver ions. We can describe things at the atomic scale, describing the ionic movement leading the above precipitation. And we can use symbolism, for example representing the ions in a diagram, or talking about the solubility product equation.  When students learn chemistry, moving between these “domains” is an acknowledged difficulty. These three domains were described by Alex Johnstone, and we now describe this as Johnstone’s triangle.

Johnstone's triangle (from U. Iowa Chemistry)
Johnstone’s triangle (from U. Iowa Chemistry)

One of my observations from the many experiments I carried out with Bob was that we can begin to see these reactions happening. The precipitation reactions took place over about 30 seconds as the ions from a salt at each side migrated through the droplet. Conductivity was introduced into the assumed unionised water droplet by shoving in a grain or two of salt. We are beginning to jump across representations visually. Therefore what has me excited about these techniques is not just laboratory work, but activities to stimulate student chatter about what they are observing and why. The beauty of the plastic sheets is that they can just be wiped off quickly with a paper towel before continuing on.

Reaction of ammonia gas (Centre) with several solutions including HCl with universal indicator (top right) and copper chloride (bottom right)
Reaction of ammonia gas (centre) with several solutions including HCl with universal indicator (top right) and copper chloride (bottom right)

Bob knew I was a schoolboy chemist at heart. “Put down that book on phenomenology” I’m sure I heard him say, before he let me pop a flame with hydrogen and reignite it with oxygen produced from his modified electrolysis apparatus (I mean who doesn’t want to do this?!). I left the room fist-bumping the air after a finale of firing my own rocket, coupled with a lesson in non-Newtonian liquids. And lots of ideas to try. And a mug.

I want a CLEAPPS set to be developed in time for Christmas. In the mean time, you can find lots of useful materials at: http://science.cleapss.org.uk/.

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2 thoughts on “A tour around Johnstone’s Triangle

  1. You are spot on about the benefits of the microscale regarding reduction of cognitive load – I was just writing about this today for one of our upcoming blogs. The ability of students to focus on a small physical area with limited equipment to minimise what they have to process gives them much more chance to make accurate observations and consider the conceptual underpinnings of the chemistry that is happening. We’ve been putting out suggested practicals for our new GCSEs based on CLEAPSS activities. One of the great advantages of the new GCSEs is that teachers can choose those activities that best suit their students, what they have available and that can really help with conceptual development. Its good to see the ideas of microscale are to be found across the educational spectrum.

  2. Really interesting piece, thank you! I teach physics – well, these days I mainly work with physics teachers – and chemistry was always my weakest area. I never got exposed to microscale chemistry at school but think it’s a really interesting approach. I play around with equivalent things for physics in the day job.

    I’m actually more interested, right now, in the Johnstone’s triangle idea. Getting kids, and teachers, to swap between the model and hands-on domains is something I’ve talked about, but this is a nice approach. More reading needed! Thank you.

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