My brilliant idea - Festive treats

12th December 2008 at 00:00
James Williams, a lecturer in education at the University of Sussex, looks at the science of Christmas

Science - Ages 11-14

One of Santa's little helpers has been mischievous. Mrs Claus made a biscuit mix of flour, baking soda and icing sugar. A naughty elf has made up mixtures that look like Mrs Claus's, but might contain unperfumed talcum powder, Epsom salts (magnesium sulphate powder) or flour.

What pupils need to do is find the correct mixture. First ask them to test each of the powders with vinegar, iodine and by heating gently in an empty aluminium mince pie tray. The baking soda will fizz in vinegar, the flour will turn black with iodine and the sugar will caramelise when heated.

Make the following mixes:

- Flour, chalk, talcum.

- Flour, baking soda, sugar.

- Talcum, Epsom salts, flour.

Get the pupils to test samples of each of the separate powders and put their results in a table. Then give each pupilgroup samples of each of the three mixtures.

Using the tests they have done as a guide, they have to deduce which mixture was made by Mrs Claus. This activity could have further combinations of mixtures to extend the lesson.

This is best done with spotting tiles so that small samples can be used when testing with vinegar and small foil trays to hold a sample of the powder that can be heated using a standard Bunsen, tripod and gauze setup. Remember to perform a risk assessment for heating and the use of iodine.

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