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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How difficult are Gas Law questions?

At last – a way to quantify if you are asking a nasty question or not!

CharlesProblem solving imposes a cognitive load on novice learners. Even if the problem is simple (often called exercises, if they involve routine algorithmic tasks), the learner will need to recall how to approach each stage of the exercise in order to solve the entire problem. Thus the question arises: if a problem involves several tasks, does each one add to the cognitive load? Which ones do learners find difficult.

This question was addressed for Gas Laws in an interesting paper in Journal of Chemical Education. The authors took typical gas law questions, and determined what processes were required to solve them. Each of these processes had a level of difficulty. For example, sometimes the number might be presented in scientific notation, or sometimes a unit change was required. The authors listed five variables that could be distinguished:

  1. The gas identity: whether it was “an ideal gas” or a “mixture of gases” or an “unknown gas”.
  2. The number format: whether it was general (1.23) , decimal (0.0123) or scientific (1.23E-2).
  3. The unit change required in volume: no change (L to L or mL to mL), or conversion mL to L, L to mL.
  4. The unit change required in temperature.
  5. The units of pressure.

From this, questions of different complexity could be derived using all of these variables – in total a possible 432 combinations. These range from easy questions where no conversion was required, to difficult questions where conversions were required. The authors then analysed several thousand answers from chemistry and non-chemistry major students in their first year. Based on what was involved in each question, they could determine what was causing least and most difficulty. Read paper for lots of statistics—I’m going to highlight the results.


The results are interesting for two reasons: they identify for this particular set of questions what variables caused most difficulty, and more so, the authors generate a cognitive load increment for all items ranging from those which don’t cause a significant cognitive load to those that do. I think it is an interesting way to present the data. The load was given a rating of 0: no additional load increment; 0.25: small effect; 0.5: medium effect; 1: large effect.  The total cognitive load increment for a question is determined by adding up the individual components.

Of the five variables listed above, only two showed significance in the analysis.

  • The number format: If the number was in scientific notation, this caused difficulty (a cognitive load increment of 0.5). Decimal format had a smaller effect (0.25).
  • The volume conversion: interestingly, if students were given L(itres) and need to convert to mL, this had a significant load associated with it—the largest observed. The conversion in the other direction also had a significant load, although the former was perceived to be more difficult, as it involved dividing. Both were assigned a load increment of 1.
  • Additionally, there was marginal significance for the temperature value – providing and requiring °C (i.e. have to convert through K). this had an increment of 0.5.

Thus a very easy question would be that shown below (given in the paper – complexity factors in bold). No conversions are required and the number format is general. This has a cognitive load increment of zero according to the authors’ scheme.

An ideal gas occupies an initial volume of 6.22 L at a temp of 262 L. What is the final volume in units of L if the temperature is changed to 289.6 K while the pressure remains constant.

On the other hand, this whopper is a hard question. Scientific notation and unit changes abound, and this has a cognitive load increment of 2.25:

A mixture of ideal gases (…) occupies an initial volume of 3.21 x 106 mL at a temperature of 62.8 °C. What is the final volume in L(itres) if the temperature is changed to 89.6 °while the pressure remains at a constant value of 1.2 atm.

Now its time to analyse our gas law questions – are we being too easy or too hard?!


J. D. Schuttlefield , J. Kirk , N. J. Pienta , and H. Tang, Investigating the Effect of Complexity Factors in Gas Law Problems, Journal of Chemical Education, 2012, 89, 586-591. [Link]

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Do you use lecture handouts, and when?

The aim of the “Journal Club” is to present a summary of a journal article and discuss it in the comments below or on social meeja. The emphasis is not on discussing the paper itself (e.g. methodology etc) but more what the observations or outcomes reported can tell us about our own practice. Get involved! It’s friendly. Be nice. And if you wish to submit your own summary of an article you like, please do. (Paper on author’s website).

4. EJ Marsh and HE Sink, Access to Handouts of Presentation Slides During Lecture: Consequences for Learning, 2010, Applied Cognitive Psychology, 24, 691–706.

As class sizes get bigger, and photocopying notes becomes more time-consuming, I thought it would be interesting to have a look at this study on whether and when to give students handouts to lectures. The authors have devised two scenarios: students are given the handouts at the start of the lecture or students are given the handouts after the lecture is over (this would drive me INSANE if I were a student!).

The authors argue that cognitive load theory has something good to say about both options. Providing material in advance helps students encode the lecture information more readily. Providing the material afterwards means that the students have to work a bit harder during lectures, but that this work can be a benefit to learning (“desirable difficulties”).

They constructed scenarios whereby students watched a lecture, either with or without handouts. They examined students scores in a test soon after and one week after the lecture, to study the difference in short and longer term recall. A separate prior study found that 50% of staff preferred to give handouts before a lecture, 21% saying they never distributed their notes. 74% of students preferred notes before the lecture.


The authors first examined the number of words written by students who had and had not handouts. Unsurprisingly, those without wrote twice as much as those with handouts. When this text was analysed, it was found that the bulk of the extra text written by the no-handout group was text from slides. Interestingly, there was no difference between the two groups in terms of the amount of text written that was not on slides – it was the same for both groups.

Performance in the tests both immediately afterwards and one week after related to the amount of time students reviewed the material, but not to whether students had handouts in the original lecture. A caveat here is that students who did not have handouts spent slightly longer on lecture review. The authors summarise this observation by saying that the end result for both groups was the same, although it took the no-handout group more effort to get there. I think this is an interesting discussion point.

A second experiment which tested free recall soon after the lecture found that students with handouts performed slightly better (significant to 0.05).


This is a small study but throws some interesting light on some common myths that appear on both sides of the argument. Giving handouts in lectures did not significantly enhance any additional note taking by students in the time they had available to amend the notes they were provided. Similarly, requiring students to write out the text did not improve memory of the material. The students who did not have handouts had to do a bit more work to achieve the same grade as those who were given handouts.

1. Do you use handouts? Do you give them out before/after? Why?
2. What’s your opinion on the “extra work” by students result – do you think it is a good thing that students without handouts acheive the same score by virtue of spending more time reviewing the material?

In other words, do I need to go to the photocopier tomorrow?!

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