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Identify Pure Substances From Their Melting and Boiling Points

In this worksheet, students will learn how boiling and melting points can be used to identify pure substances.

'Identify Pure Substances From Their Melting and Boiling Points' worksheet

Key stage:  KS 3

Year:  Year 8 Science worksheets

Curriculum topic:   Chemistry: Pure and Impure Substances

Curriculum subtopic:   Identifying Pure Substances

Difficulty level:  

Worksheet Overview

In chemistry, we refer to a pure substance as being a substance made from only one element or one compound. And nothing else.


Pure elements and compounds have specific melting and boiling points, which means they will always melt or boil at exactly the same temperature. For example, pure water has a melting point of 0°C and its boiling point is 100°C. If the melting or boiling point of a substance doesn’t match the correct value, the substance cannot be pure and must be a mixture/impure. 


two thermometers


The opposite of a pure substance is an impure substance. An impure substance is one made from more than one element or one compound, meaning it is a mixture.


Impure substances or mixtures melt and boil over a range of temperatures, so may have a melting point of 34-39oC for example, depending on the exact composition of the mixture. 


Pure substances and impure substances can be identified by comparing their melting point with published reference data of what the melting point should be.


Think you can work out whether a substance is pure or impure just from its melting or boiling point?


Let's try some questions.


girl on computer

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