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Science Y6 – Materials and their Properties – week 8

REVERSIBLE CHANGES

Truth to Teach (Source)

 Some chemical changes are reversible and some are irreversible.

 The reverse of melting is freezing.

 The reverse of evaporating or boiling is condensing.

 Melting describes a solid turning into a liquid.

 Different solids melt at different temperatures.

 Separating chemicals.

 Reversible changes produce no new materials.

Way to Work (Means)

Equipment: Magnets, sieves, funnels, filters, jars, pots, saucers, blotting or absorbent paper, felt-tip pens, water

1. Review the previous lessons.

2. Explain the meaning of reversible and irreversible changes as applied to chemistry. Most solids, liquids and
gases can change state from one to the other, e.g. chocolate can be melted and reset, water can be boiled to
form steam then condensed, candles can melt then reset, liquid iron can be poured into a mould and become
hard, molten lava from a volcano becomes hard.

3. Divide the children into groups to work with some reversible changes. Provide them with lots of equipment.

a) Separating sand, gravel and water using sieves and filters.

b) Separating salt and water once salt has been dissolved in it, by evaporation.

c) Separating peas, sugar and paper clips with a magnet and sieve. Use water to dissolve the sugar.

d) Separating iron filings, sand and salt using a magnet. The rest should be separated by
evaporation.

4. Gather back to share results.

5. Think of examples of liquids turning to gas (evaporation), e.g. clothes drying on a line, puddles drying up, our hair
drying. Discuss ways to speed up evaporation, e.g. hair driers, tumble driers, fires or something else to increase
the temperature of the air.

6. Talk about gases turning back to liquids (condensation). Condensation is caused by water vapour hitting a cold
surface and becoming colder, e.g. steam on a metal spoon, warm breath on a mirror.

7. Discuss reversible changes being possible when:-

a) Insoluble materials are mixed in water.

b) Solutes are dissolved in water then the solution is left to evaporate. (Liquid to solid)

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