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Some kinds of ‘stuff’ (wax, for example) are single substances; others (for example, chocolate) are mixtures of substances.

A sample of stuff that is just one substance has an exact melting point - a particular temperature where it changes from the solid to the liquid state.


A sample of stuff that is a mixture of substances does not have an exact melting point.

If a sample of stuff is just one substance we say it is a pure sample of the substance.

Notes: see Teachers’ Guide
teachers’ guide f1

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f1: melting
f2: stuff
f3: air

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