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Science Y6 – Materials and their Properties – week 9
IRREVERSIBLE CHANGES
Truth to Teach (Source)
Chemical changes can be irreversible.
Most substances, when burned, cannot be changed.
The assessment of the dangers involved in burning substances.
Making pancakes or Play dough
Way to Work (Means)
1. Review the previous lesson.
2. Discuss the meaning of reversible and irreversible changes.
3. Irreversible changes involve the forming of new materials which cannot be changed back to the original, eg wood
to ash, cooked bread or cakes.
4. Let the children complete the worksheet then spend time cooking (and eating) pancakes, or making Play dough to
illustrate irreversible changes.
Pancakes Play dough
One egg Two cups of flour
250 ml milk One cup of salt
100 g flour One cup of water
Pinch salt 4 tsp cream of tartar
1 tabs melted fat 2 tsp cooking oil
Sift flour and salt into a bowl. Warm the ingredients in a pan
Beat to a creamy batter with egg, over a low heat, stirring all the time.
half the milk and melted fat. Stir in When it begins to thicken, leave to
rest of the milk. Brush frying pan with cool.
melted fat and warm. When pan and
fat are hot, pour in the batter and fry on
both sides. Serve with sugar and/or lemon.
5. Discuss the irreversible changes involved in these processes.
• Some things cook when you heat them and they completely change.
• Some things burn when you heat them and they change completely.
• Both changes are irreversible.
6. Talk about other irreversible changes, e.g. frying an egg, adding water to cement, burning paper or wood.
7. Briefly discuss the dangers of burning substances which we do not know about.
These could produce undesirable and harmful results. Talk about furniture made from combustible materials.
Learning for Life (Fulfilment)
The children should be able to recognise irreversible chemical changes and be aware of the dangers of burning
substances. They will also know how to make pancakes and/or Play dough!
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