1. Organising group work to make and evaluate an indicator
Sometimes, especially when they are learning a specific technique, students will need detailed instructions about what to do. However, if they are going to develop an understanding of what it means to be a scientist and the confidence to think for themselves, then you need to give them the opportunity to take part in open-ended investigations. During the planning, carrying out and evaluating of an experiment your students will really have to think about what they are doing and why they are doing it. Extracting an indicator from a plant is a good opportunity to let your students think for themselves. They need to know examples of acids and alkalis, but they are unlikely to be asked to describe the method in great detail. If they don’t do quite as you expect then it doesn’t really matter; they will get a great deal of satisfaction from working it out for themselves.
It is likely that some of your students will have heard of the term ‘acids’. The first activity describes an experiment in which they will make an indicator from flower extracts and use it to test different substances. This topic is a good opportunity for you to ‘let go’ and take a risk! You will show them what to do, but not give them detailed instructions (Resource 1 provides some background for the teacher and Resource 2 explains the importance of doing a risk assessment). Leave them to plan the details in their groups. They will get the most out of this sort of activity if you give them the opportunity at the end to think critically about what they did and how they could have done it better.
Case study 1: Groups plan their experiment
Mr Otieno, a student teacher at Achego Secondary School, prepared a class practical and evaluated it for one of the assessments tasks on his BEd (Science) course. In a previous lesson, the class had tested various household substances with litmus. Now he wanted them to make their own indicator. On Monday morning, Mr. Otieno walked into class with a bundle of leaves and flowers from different plants. He gathered the class round the front and showed them how to extract the colour from a plant. He asked the students to form six groups of about seven students. Each group was to consist of both boys and girls and it had to contain at least two girls. He asked each group to choose a leader. Mr Otieno asked the students to draw a plan for making and testing the indicators from the plant material. The leader had to make sure that everyone had a job. He then asked each leader to come to the front bench to collect a set of flowers (red flowers and blue flowers) and green leaves plus the apparatus they needed.
When the students were working, Mr. Otieno moved from one group to the other posing questions and making sure that everyone was involved – particularly the girls, who he had noticed often hung back.
He asked the students to test the indicators with a variety of household substances and to record their observations in their exercise books. He asked each group to decide which flower made the ‘best’ indicator and to explain how they decided. Ernest’s group thought the red flower was best because it gave a very dark colour. Mary’s group thought the blue one was best because there was a big difference between the colour in acid and the colour in alkali. It also distinguished between a weak acid and a strong acid.
Activity 1: Evaluating the experiment
Gather your class round the front. Show them how to make an indicator and test it.
Their task is to prepare at least two different indicators and to use them to test a variety of substances. Divide them into groups and get them to make a plan. They should make a list of the apparatus they need to collect and decide who does what job. Each group should choose a leader. When you are satisfied with their plan they can start. They should make and test at least two different plants. While they are working, you should move around the room and ask them questions about the method.
At the end of the activity give them the chance to look at the samples that other people have prepared. Ask each group to evaluate their experiment.
- Did they get some good samples?
- Did they manage to test several different substances?
- What have they learnt from the experiment?
- Did the leader do a good job?
- Did everyone make a contribution?
- How could they have improved their experiment?
- Did they make efficient use of the time available?
By encouraging them to think about the activity in this way, you will ensure that next time you ask them to work in groups on an open-ended activity, they will do it better.