Science - Cooking up a stink

30th September 2011 at 01:00
Pupils can enjoy scientific discovery in their homes

Baking cakes with children is fun, if messy. But how many times have you encouraged parents or guardians to do some science at home using chemicals they can find in the kitchen cupboard? Cornflower, salt, sugar, water and red cabbage can be used to demonstrate science at home.

There are many similarities between cooking and science. Changes of state (freezing and boiling) are routine observations made in a kitchen. Evaporating salt (or sugar) from water to separate the solid crystals is a simple experiment. Seeing if warm water dissolves more salt than cold water is a safe, simple investigation that can be done at home. A competition, such as who can grow the biggest salt or sugar crystal, can add interest.

A messier experiment uses cornflour mixed with water. With the right proportion of water and cornflour you find that the faster you stir, the stickier it becomes. If you make the right consistency, when you apply pressure to a handful of the mixture by squeezing it hard, it appears to thicken and become more solid. When you release the pressure, it turns back into a fluid. This can be compared with another household favourite, tomato ketchup, which does the opposite. It is normally quite thick and doesn't flow well, but if you shake it hard it flows. Both are what scientists call "non-Newtonian fluids"; they don't behave as they are supposed to. Getting children to predict what they think will happen and to write down what they can see and, in the case of cornflour, feel, is part of the process of being a scientist - making predictions, looking at what happens and noting down observations. Pupils don't need to know about non-Newtonian fluids, but challenging their intuition does help them with their thinking skills.

Cooked red cabbage is not every child's favourite, but the deep-purple liquid produced gives you a good chemical indicator once cooled. Indicators can tells us about the properties of other chemicals: for example, acids and alkalis turn indicators different colours. In the case of the cabbage water, an acid such as vinegar will turn a few drops of the indicator red. Bicarbonate of soda dissolved in water will turn the indicator blue. At home, children could test liquids from lemonade to rainwater to see if they are acid or alkali. Clear liquids will work best, but tell the parents to avoid cleaning chemicals - they should always be handled with care and not used in home experiments.

Growing simple plants at home, from cress to broad beans, will let children experiment with different conditions to see what affects how plants grow - your pupils could keep "growing" diaries. In summer, try a sunflower-growing competition.

Engaging pupils with kitchen science helps build a bond between school and home. Parents often want to help their children, but need just a little bit of guidance. So why not think about how some simple experiments you do in school could be useful home-based investigations and send out a newsletter with some ideas.

James Williams is a lecturer in science education at the University of Sussex, school of education and social work.

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