Practical work: a new opportunity

For teachers in England and Wales, the introduction of new A-level chemistry specifications has brought practical work back into the spotlight. The straitjacket of assessed tasks is gone. Teachers have a wonderful opportunity to plan the practical work they want to do, ensuring students develop skills throughout their course. How can they make the most of this opportunity to get the best out of practical work?

The importance of objectives

There are lots of reasons for doing practical work: developing a skill in a particular technique; providing an opportunity to solve problems; helping develop conceptual understanding; or simply demonstrating chemical change. Teachers need to be very clear about the specific reason for choosing each experiment. This principle has been well documented in the Getting Practical¹ initiative. Teachers must set precise and realistic objectives when planning experiments and check how well they have been achieved at the end of the session.

The objectives should always be shared with students so they know why they are doing the work.

The biggest danger is trying to squeeze too many outcomes from a single experiment. It is much better to use several sessions to build skills in a manageable way.²

The checklist in Box 1 gives some questions teachers can use to make sure they are aiming in the right direction.

Focusing on the task

There is a danger that practical work can become for some students a ‘painting by numbers’ activity. They perceive their job as simply following instructions to complete the task. Their focus is purely ‘hands-on’. But practicals can easily be made ‘minds-on’ by encouraging students to question what they do and make sense of what they observe (Box 2).

Students need to be engaged to make effective links between what they see and the conceptual ideas they are trying to develop.

Research suggests teachers should spend more time making explicit the ideas an experiment is designed to illustrate rather than assuming they will simply emerge from what the student has measured or observed.³ This means devising in advance questions students can use to check their understanding of experimental procedures and results. Asking students to discuss their experiments in groups is an effective way of making these vital links between observation and ideas. Yes, it takes time. But what is the point in spending a shorter time on experiments students get nothing out of?

Learning to investigate

Students often find it difficult to plan an investigation. Maybe that is because we don’t give them sufficient opportunities to develop this skill. Investigations don’t need to be complicated. Reducing information or limiting available equipment can transform a recipe driven activity into one in which students have to work out what to do themselves. In Box 3 an acid base titration, tests for anions and cations and the ideal gas equation form the basis of straightforward investigations for students.

Variety in practical work

Practical work can easily become very repetitive (some might say boring) with students mostly working in pairs on a test tube scale following teacher produced handouts. This is particularly true for the most able students, a group often insufficiently engaged by practical work. Changing your approach from time to time can be stimulating.

Some experiments lend themselves to whole class activities in which results are pooled and used to come to an agreed conclusion. Finding the most cost effective brand of bleach is a good example. Instead of everyone carrying out the same iodine-thiosulfate titration, groups of students are given different bottles of bleach to analyse. They combine results so they can come to an overall judgement.

Students might be forgiven for thinking all chemistry experiments can be carried out in under an hour because they always fit neatly into one lesson. The preparation and purification of aspirin is an opportunity to carry out an extended two step synthesis over several sessions, developing some key practical skills along the way (see table below).

Experiment	Practical skills developed
Converting methyl 2-hydroxybenzoate (oil of wintergreen) to 2-hydroxybenzoic acid (salicylic acid)	- Devising a risk assessment - Setting up glassware using retort stand and clamps - Heating under reflux - Filtering under reduced pressure
Converting 2-hydroxybenzoic acid to impure 2-acetoxybenzoic acid (aspirin)	- Devising a risk assessment - Safely handling solids and liquids including corrosive substances - Filtering under reduced pressure
Purifying and analysing 2-acetoxybenzoic acid	- Recrystallising a solid - Thin layer chromatography - Melting point determination - Calculating percentage yield

Carrying out experiments on a reduced scale has clear benefits in safety and economy of materials. It also helps students develop the skill of careful observation. Bob Worley at CLEAPSS has documented some excellent examples⁴ of reduced scale experiments that can easily replace more traditional methods (see Box 4).

Small scale experimentation also offers the opportunity for students to work individually. Most of the time, students work in small groups, which can lead to some being passive observers in practical sessions. Asking students to work on their own from time to time is a really good way of making sure that everyone is actively involved in developing their skills.

Contextualising practical work

Contexts can bring practical work to life. It helps students appreciate that chemistry and the work that chemists do are an important part of the world around them. A simple change in the choice of experiment to illustrate a topic or idea can make the activity much more engaging. Some examples are shown in the table below.

Standard experiment	Contextual alternative
Iron(II) sulfate–manganate(VII) titration	How much iron is in dried thyme?
Thiosulfate–iodine titration	How much sulfur dioxide is in a bottle of wine?
Effect of temperature on reaction rate using sodium thiosulfate and acid	Effect of temperature on the reaction between stewed rhubarb and potassium manganate(vii) solution
Paper chromatography of inks	What’s in artificial sweetener tablets?

Integrating skill development

To satisfy the new A-level practical endorsement requirements, students must carry out a minimum of 12 practical activities and develop competence in a range of skills. Some teachers may treat these activities in isolation, to be undertaken and ‘ticked off’ at stages throughout the course.

However, meeting the requirements of the practical endorsement should be a consequence of practical activity, not the reason for doing it.

This is the most important aspect of effective practical teaching. Students develop experimental skills to be able to apply them, not for their own sake.

You should aim to integrate the skills a student needs within an overall scheme of practical work. So a student will recrystallise a solid, not because they have to satisfy the practical endorsement, but because they want to produce a pure sample of aspirin (see Table 1),⁵ and they will use a pH meter because they want to investigate the difference between strong and weak acids.

Derek Denby is an independent science education consultant based in the UK with a particular interest in practical work.

More CPD

The Royal Society of Chemistry’s Developing Expertise in Teaching courses are designed to support you throughout your teaching career. Practical work is an integral part of all face-to-face workshops.

To find out more about the CPD for Teachers courses on offer, visit http://rsc.li/teacher-cpd