Marking, methods and moles

I was prepared for the full days, the nearly empty social calendar and the frustrations with applying mark schemes I didn’t fully agree with. But I had no idea how much it would impact my teaching.

Not only did I discover how generously I had previously applied mark schemes, but I was also surprised how much time my students and I wasted with unnecessary detail. The biggest surprise, however, was how specific the students’ choice of language had to be; if one key word was missing, several marks of good chemistry could go uncredited.

So, to the age-old question: are we teaching students to understand chemistry or pass exams?’ I still reply, ideally both. Hopefully, the lessons I have learned examining will help you on your journey towards striking that balance.

The amount of time and energy I used to spend getting my students to add detail to their extended response answers was huge – particularly when writing methods for practicals.

Don’t be put off by the plethora of bullet points in some mark schemes, labelled as indicative content, or similar. Students usually only need five or six specific points for full marks; the rest are superfluous.

If learners are planning an investigation, the only points required seem to be:

• How much of each reactant is needed, and how will it be measured?
• How will you set up the apparatus and mix the reactants?
• What are you measuring during the experiment, and how?
• When do you start and stop measuring?
• What do you change when you repeat the experiment (reminding students to refer to the question)?
• What must stay the same each time?

With methods such as titration, salt prep and chromatography, there are just five or six essential pieces of information that students need to remember.

I now approach exam-focused method-writing like this:

• Outline the level descriptors, then give the students a question to answer.
• Distribute the mark scheme and ask students to identify which points in the indicative content are essential and which are not.
• Have a class discussion explaining why each bullet point is, or isn’t, essential.
• Peer- or self-assess answers.
• Mark students’ marking until they can apply mark schemes as well as you can.
• Repeat the same (or similar) question a few lessons later or write down a model answer.

I find this strategy helpful with all abilities. More able learners seem less inclined to get bogged down in detail and perhaps miss a key step. Super-keen students, who tended to go onto additional paper, wasting precious time, learn to limit themselves to six to eight bullet points. Less able students find focusing on a few key ideas less overwhelming than a long list of bullet points.

Of the many ways of teaching these calculations, I’ve always favoured the moles method, believing it’s the best preparation for post-16 study. Using a table to guide less able students is helpful, although often these learners know the method worked but have no idea why.

Having marked a limiting reagent question, unsurprisingly, most of the students who got full marks used the moles strategy. Of those who didn’t get full marks, students using the moles strategy, with or without a table, tended to score fewer marks than those who calculated what 1 g of the reactants would make, then scaled up.

I have since started using this latter approach with my lower-attaining students and found that their scores and confidence have greatly increased. I provide a fair amount of scaffolded practice but, once the penny drops, students often retain this concept better over time, perhaps because it is less abstract than using moles.

Marking points for bonding questions are often lifted directly from the specification, and the language required is very specific. For example, through is not the same as throughout. Delocalised electrons must carry charge, not current. They must also transfer thermal energy, not heat. And that’s only the metals section.

I was expecting this fastidiousness at post-16, but don’t underestimate how strict 14–16 examiners are told to be. Mark scheme requirements can seem to alter year-on-year, so using exact specification language is undoubtedly the safest teaching approach.

These are certainly the most time-consuming questions to correct, and students often make an absolute hash of them. Furthermore, bond enthalpy questions tend to add another layer of complexity, requiring rearrangement of the ΔH expression to calculate an unknown bond energy.

The table below (with less scaffolding for higher achievers) has helped my students get extra method marks. It shows up arithmetic errors more clearly, making it easier for examiners to follow students’ working.

If an unknown bond enthalpy is required, there is much less to go wrong when students rearrange the final equation in this table, rather than trying to rearrange earlier on.

As I continue to examine, I will gain new insights, which will further inform my teaching. The benefit of marking to my classroom practice is beyond question – it’s one of the best forms of CPD I have undertaken. The next step? Probably to mark AQA’s paper 2, but I’m not sure I can bring myself to willingly face 600 life cycle assessments … yet.