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TGD1: Substance and State
Notes on the animation.
The set of questions reinforces the points on substance and state, and also the specific point made in the language alert. It is a relatively quick activity which would work well as a class voting activity or asking individual students to choose an answer.

Language alert
In everyday language we often use phrases like ‘Oxygen is a gas’. We should say, ‘Oxygen is in the gas state at room temperature’.
Solid, liquid and gas are not three separate types of substance, they are the three states a sample of any substance could be in.
The state of a substance depends on its temperature and on the melting point and boiling point of the substance.

Beware of using phrases which may cause some students to think that solids, liquids and gases are themselves different types of substance.

For example,
‘Oxygen is in the gas state at room temperature’ is a better statement than ‘Oxygen is a gas’ because it tells you the substance, the state and the temperature. Similarly, ‘These substances are in the solid state at room temperature’ is correct, whereas ‘These substances are solids’ is misleading and could reinforce a student’s misunderstanding of substance and state. The 'Features of Students' Understanding' section of the Teachers’ Guide considers this issue in more detail.

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