Practical work and cognitive load - David Paterson 03 February 2017

In this blog post I consider the dangers of overloading practical lessons with too much for learners to take on, and give an example of how learning can be broken down to better support understanding.

Practical work is expensive, in terms of both budget and lesson time. To justify the use of practical work in teaching and learning, it is important to ensure that it provides the maximum benefit to the learners. Beyond the practical work requirements in the new science GCSEs, practical work can help develop conceptual understanding and increase learner motivation. However, careful account needs to be taken of the cognitive load put on learners when they are carrying out practical work.

My early experiences and expectations

This was most clearly brought home to me when I first taught titration at GCSE. Having recently used titration with an A-level class, I made the (pedagogically) fatal mistake of starting the lesson with a demonstration of a simple acid–base titration and then setting the class off on a ‘follow the recipe’ practical to determine the concentration of an alkali solution. I spent most of the rest of the two hour lesson moving from group to group re-explaining what they were doing and re-demonstrating the techniques. By the end of the lesson, little of consequence had been learnt by the majority of the learners. For me, however, it was a salutary lesson in the importance of careful planning and scaffolding of complex tasks.

Accurately finding out the concentration of a solution by titration involves a wide range of competencies. As teachers we ‘see’ this task in a very different way to novice learners. We have internalised all our practice over the years, and can understand and focus on the final result without getting bogged down in the details. By contrast, learners can easily get overwhelmed by the intricacies, and end up just ‘following the recipe’ without having any real understanding of what they are doing and why they are doing it. 

What methods can help expedite the understanding for new learners?

Learners new to titration face the challenges of engaging with new equipment, making accurate observations and measurements, thinking about what is happening at the microscopic level, carrying out calculations and dealing with the noise of a room full of their peers (and everything else inherent in being a teenager at school!). There is simply too much to process if all of this is introduced in one go, so learners need help through carefully scaffolded steps.

An example approach at GCSE would be:

1. Recap of neutralisation and use of indicators.
2. Carry out ‘The vinegar dilemma’ – this is one of OCR’s suggested activities for the Titration Practical Activity Group. It is a gravimetric titration, using simplified equipment and a ‘black box’ calculation, and helps learners to make connections between concentration and volumes of liquids.
3. Introduce the volumetric pipette, and have learners practice with deionised water.
4. Introduce the burette, and have learners practice with deionised water, perhaps introducing an element of competition to identify the best learner in each group at accurately taking volume readings.
5. Use interactive activities to allow learners to learn and make mistakes in a low-stakes environment.
6. Carry out a standard hydrochloric acid–sodium hydroxide titration.
7. Discuss the chemistry of strong and weak acids/bases, using the ‘Acid Strength’ activity from the ‘Chemical misconceptions’ publication.
8. Introduce an investigative aspect by supplying other acid–base indicators and acids/alkalis of unknown concentration.
9. Consolidate understanding of the calculations with plenty of example calculations and problems for the learner to solve.

Ultimately, the decision on how to use practical work is in your hands. OCR has provided suggested activities, and some (optional) tracking tools to help, but there is no requirement to use these. If you plan and teach your subject well, the practical requirements of the specification should be more than covered, and your learners will be well prepared for their exams.

Submit your comments below, and if you would like to get in touch with us then please email us via science@ocr.org.uk or send your tweets to @OCR_Science

About the author

Dr David Paterson - Subject Specialist - Chemistry

David joined OCR in September 2015 to support teachers in their delivery of A Level and GCSE Chemistry and Science. He is particularly interested in teacher training and development, and improving teaching methods in the classroom. He was previously Head of Science and Physics at Hitchin Boys School, and Head of Science and Chemistry at Meridian School, Royston. His post-doctoral and doctoral research was in researching novel anti-cancer kinase inhibitors. In his spare time he practices martial arts and plays to the French horn.