GoalRemember solids and liquids, melting and freezing, and mixing and baking.
New words
solid · keeps its own shapeliquid · flows and takes the shape of its containermelt · to change from a solid to a liquid when warmedfreeze · to change from a liquid to a solid when cooled
Explanation
A solid keeps its own shape. A liquid flows and takes the shape of its container. When a solid gets warm, it can melt into a liquid. Ice, butter and chocolate melt. When a liquid gets cold enough, it can freeze into a solid. Melting and freezing can go both ways. Some changes cannot go back. When we mix flour, eggs and butter and an adult bakes the mixture, we get a cake. A cake cannot become batter again. Only a grown-up uses the oven or the cooker.
Change
Can it go back?
chocolate melting
yes: it can set hard again
water freezing
yes: the ice can melt
baking a cake
no: it is a new material
Worked examples
Lola pours juice into an ice-lolly mould and puts it in the freezer. A few hours later the juice has frozen. It is a solid and does not pour.
When the sun comes out, a snowman melts. The solid snow turns into water. On a freezing night, the water can turn back into ice. This change can go back.
Grandad toasts some bread. The soft bread turns hard and brown. Toast cannot turn back into soft bread. This change cannot go back.
Class activity
Sort the changes (with an adult): write these changes on small cards: ice melting, water freezing, baking bread, cooking an egg, melting chocolate, mixing squash and water. Think about each one: could you change it back? Make two piles, “can go back” and “cannot go back”. Which pile has the baking?
Practice
1
What is the name for a liquid turning into a solid when it gets cold?
Freezing.
2
Which two of these are liquids?
A, the juice and C, the water.
3
Ali leaves a bar of chocolate in a hot car. What happens to it? What happens when it cools down?
It melts and turns soft and runny. When it cools down, it turns solid again.
4
Can a baked biscuit turn back into soft dough? Why or why not?
No. Baking made a new material, and the change cannot be undone.
