Teaching science in primary school can be challenging. Astrid Kaiser and Marlene Rau describe a rich source of online materials in three languages – and highlight some activities about oil and water.
Launched in 2002 by Astrid Kaiser from the University of Oldenburg, Germany, the LeSa21 websitew1 offers a range of experiments, resources and background information for primary-school science and humanities lessons. Materials for both teachers and their pupils are available on a wide range of topics (currently 93), including ‘The eye’, ‘bicycles’, ‘spring’, ‘health and disease’, ‘girls and boys’, ‘planets, the Moon and the stars’, ‘electricity’, ‘water’ and many others. These materials are developed mainly by university students who are training to be primary-school teachers.
Available in English, German and Spanish, the ‘Learning’ section is suitable for both children and teachers, and includes experiments, stories, poems, pictures, book recommendations and links to relevant websites for each of the topics.
The pages for teachers (in German only) contain information, didactical hints, literature and web links to background information and further resources on each of the topics. Pupils at the six schools involved in the project contribute to further German-language sections. There, they can share their own experiments and ideas on the topics, and discuss a selection of the topics in an online forum.
Below are some activities from the LeSa21 project, which could form the basis of a teaching unit on oil and water, including surface tension and the removal of oil spills, suitable for older primary-school children. The individual experiments and further materials on the topics can be found on the LeSa21 websitew1.
This experiment introduces the notion of surface tension.
Initially, both the pepper and pin float. One reason is that they are both very light; the other is that water has a kind of thin, invisible ‘skin’ on its surface. Light things do not break this skin, but are supported by it – some animals, e.g. water striders, can even walk on it (see image above). This thin skin is caused by surface tension.
When you added the soap drop, the pepper probably moved away from it and slowly sank. The pin would have sunk immediately.
Why is that? The soap breaks this thin skin of the water – you could also say that soap reduces the surface tension. As the skin disappears, there is nothing left to hold the pepper and the pin on the surface of the water, so they sink. Although this is how it may look, pepper and soap do not repel each other – the tension of the rest of the water (where the soap has not yet reached) pulls the floating pepper away from the soap.
Oil and water usually do not mix well. The reason is that water molecules can form hydrogen bonds with each other and with hydrophilic (‘water-loving’) molecules, but not with oil-like hydrophobic (‘afraid of water’) molecules. In addition, oil is lighter than water; it has a lower density, so if you try to mix them, the oil layer stays on top of the water. If you add some soap and stir it for a while, the oil and water can be mixed together. If you leave it for a while, the oil and water will separate again.
Why is that? Soap contains special ingredients called surfactants, which reduce the surface tension of water and allow water and oil to mix. This makes soap a wonderful cleaning agent: not only water-soluble dirt but also oily dirt can be washed away into water.
Surfactant molecules have two different ends, as shown in the diagram (right). One end (the head) is hydrophilic; the other end (the tail) is hydrophobic. Soap contains many surfactant molecules, and each of them binds water at one end and oil at the other end, which is how they help water and oil to mix, and also bind to oily dirt.
After a while, the oil and water separate again, because the bonds between water molecules are more stable than those between the surfactant molecules and the oil or the water.
In April 2010, an explosion on the oil rig Deepwater Horizon in the Gulf of Mexico led to a catastrophic oil spill. As we go to press, an estimated 5000-100 000 standard barrels of oil per day have been leaking out for several months, the spill eventually reaching the southern coasts of the USA. Attempts to remove the oil included burning it and using chemical and mechanical binding agents.
Similar accidents have happened in Europe, too: in Autumn 2002, the oil tanker Prestige was involved in an accident off the Spanish coast and sank. Up to 63 000 tonnes of oil were spilt into the sea, and hundreds of kilometres of the coastline of northern Spain and France were polluted with oil. Many animals died: more than 18 000 oil-contaminated birds were counted. Many volunteers helped to clean the beaches, and special ships tried to stop the growing oil slicks.
Let’s find out what oil does to bird feathers and how we can remove the oil from the water.
See how they stick together and imagine what effect an oil spill would have on birds and other animals, once the oil reaches the shores.
How might oil spills be cleaned up in open water, to prevent them from reaching the shores?
We will test various methods of removing the oil from the water. Either ask the children to get into groups, with each group testing a different method, or let the whole class watch as you try out all methods together.
Compare and discuss the results of the experiments. The children should realise that the best results are achieved with a combination of (mechanical and chemical) methods. They may also consider the factors affecting the efficiency of each method, e.g. the volume of removal agent used. Finally, they should notice that there will always be some oil left in the water at the end; in real-life situations, we have to rely on the ecosystem to deal with this remainder over time.
Which other methods of cleaning the water can you imagine? Let the children come up with some ideas for real-life ‘oil spill removal machines’. Ideas might include a ring of cat litter to stop the oil from floating away, plus mechanical diggers to remove the floating oil film.
The origins of Lesa21 go back to the RÖSA projectw2, which is still continuing at the University of Oldenburg. Since 1994, images, stories, experiments and background information for primary-school science and humanities lessons (Sachunterricht) have been sorted by topics and collected in boxes that local teachers can borrow.
The experimental equipment in the boxes is mostly recycled material found in standard households or industry, such as broken mirrors, pipettes from empty medicine bottles, boxes of old buttons, stones and used guitar strings. The objects not only provide an inexpensive source of experimental equipment, but also demonstrate to the children that materials can be used over and over again in different and creative ways. Individual boxes have been created on 70 different themes, many of them the same as the current LeSa21 topics. The ideas and materials are tested in local schools by university students and trainee teachers.
Several satellite Lernwerkstätten offer similar collections of boxes, mainly in schools across northern Germany, but also at the Pädagogisches Beratungszentrumw3 (education centre) in Brixen, northern Italy. In addition, a book has been published for Japanese teachers, who are now also working with the box system (Kaiser et al., 1999).
The two experiments ‘Soap has magic powers’ are part of the book Chemie in der Grundschule (Chemistry in Primary School; Kaiser & Mannel, 2004). Published in German, it contains many other experiments on different topics.
Parts of ‘The oil spill’ experiment are from Kaiser (2009).