2. Using questioning to enhance a demonstration
One of the reasons why chemistry is difficult is that we cannot see the things we are talking about. It is full of abstract ideas. You can help your students to understand chemical words and ideas by using experiments and models to help them develop pictures of things that they cannot see. A popular experiment for teaching about elements and compounds is heating iron and sulfur to make iron sulfide (Activity 2). But there are other experiments that you can do, as Case study 2 shows. While you are doing the demonstration, you can find out if your students understand what they are seeing by asking them a series of questions. It is important to make sure that your questions challenge them. Resource 3 reminds you about the different types of questions that you should be asking. It is a good idea to plan the questions that you could ask before the lesson. Think about how you will respond to their answers. You could ask several students the same question then ask them to select the best one. You could also ask a follow-up question: ‘Why do you think that?’
After the demonstration you can check their understanding by asking them to write a short paragraph about the experiment, using the key words. By letting the students write about the experiment in their own words, you will really be able to see if they understand the key ideas. You could let them read each others’ and give feedback.
Case study 2: Demonstrating a mixture
Mr Okumbe did not have any sulfur, but he wanted to use an experiment to help his students understand the difference between a compound and a mixture. One afternoon he set out a demonstration on the distillation process for his Form 9 class (Resource 4). He gathered his students around the front bench and showed them the apparatus. The students examined the ink available and recorded its physical properties, e.g. blue in colour, a dark liquid. He then mixed the ink with water in a test-tube and asked the students the following questions:
- What happens to the ink when mixed with water?
- Does the test-tube get warm or cool down?
- What is the colour of the mixture?
- Is it possible to get the ink back from the mixture?
Mr Okumbe heated the mixture in the flask and as it got to the boil, he collected the liquid which passed through the tube into the boiling tube immersed in a beaker of cold water. The mixture was heated until most of the water in the flask evaporated. As the process was going on, he posed questions to the students. He asked some easy questions which encouraged them to watch carefully, but he also asked lots of ‘why’ questions which made them think. When he asked harder questions, he gave the students plenty of thinking time. Sometimes he asked them to discuss the answer with their neighbour, before volunteering an answer.
At the end of the lesson he asked his students to try and think of other mixtures that could easily be separated. Someone suggested salt water and they started talking about where the salt they use at home comes from and how it can be produced on a large scale. Mr Okumbe explained that along the coast of Kenya and Tanzania, there are many places where salt is produced by evaporating sea water.
Activity 2: Demonstrating Iron and Sulfur
In this activity, you will demonstrate the reaction of iron and sulfur. Resource 5 explains the details of the experiment. Before the lesson, plan a set of questions that you will ask your students, which will help them to think about the experiment.
Gather your students round the front.
Start with some simple questions:
- What is an element?
- Which one is the metal?
- What is the evidence that this is a metal?
Get your students to make predictions:
- What will happen if I mix them together?
- What will happen if I heat the mixture?
Ask some open ended questions with more than one answer:
- How could I separate the mixture?
Give them time to discuss the answer with their neighbour before they respond.
When you complete the demonstration ask some harder (higher order) questions:
- What has happened?
- How do we know that this is a new substance?
- Can you explain the difference between an element and a compound?
Finally, set them the task of writing a short paragraph about the experiment that includes the three key words – element, mixture and compound.