Simple differences between mixtures and compounds
2 marks · EasyExplain why a mixture of ethanol and water does not have a sharp boiling point.
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Because a mixture contains more than one substance, its components have different boiling points. The mixture boils over a range of temperatures as each component boils at its own temperature.
Also accept: A mixture boils over a range because it contains substances with different boiling points.
Common mistakes: Saying the boiling point is sharp like a pure substance
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Marking points
M1 · 1 mark · States that mixtures contain two or more substances with different boiling points.
A1 · 1 mark · Explains that the mixture boils over a range, not at a single temperature.
Worked solution
A mixture of ethanol and water consists of two substances with different boiling points (ethanol 78°C, water 100°C). When heated, the mixture will start to boil at the temperature where the first component boils and continue boiling as each component vaporises, so there is no sharp single boiling point.