Pure Substance Examples in Chemistry

Start with the recap, study the fully worked examples, then use the practice problems to check your understanding of Pure Substance.

This page combines explanation, solved examples, and follow-up practice so you can move from recognition to confident problem-solving in Chemistry.

Concept Recap

A sample of matter that has a fixed, definite chemical composition throughout, consisting of only one type of element or one type of compound.

Every particle in a pure substance is the same. Pure water is all H₂O — no exceptions.

Read the full concept explanation →

How to Use These Examples

  • Read the first worked example with the solution open so the structure is clear.
  • Try the practice problems before revealing each solution.
  • Use the related concepts and background knowledge badges if you feel stuck.

What to Focus On

Core idea: Pure substances have fixed properties (melting point, boiling point, density) that can be used to identify them.

Common stuck point: 'Pure' in chemistry means uniform composition, not 'natural' or 'healthy.'

Sense of Study hint: When determining if something is a pure substance, check for uniform composition at the molecular level. First ask whether every particle in the sample is identical — if yes, it is a pure substance. Then determine whether those particles are single atoms of one element (element) or molecules made of two or more elements bonded together (compound). Finally, remember that fixed melting and boiling points are hallmarks of pure substances.

Worked Examples

Example 1

easy
Distinguish between a pure substance and a mixture. Give two examples of each.

Solution

  1. 1
    A pure substance has a fixed composition and distinct properties: elements (e.g., gold) and compounds (e.g., water \text{H}_2\text{O}).
  2. 2
    A mixture is a combination of two or more substances in variable proportions: (e.g., salt water, air).
  3. 3
    Mixtures can be separated by physical means; pure substances cannot (compounds require chemical methods).

Answer

\text{Pure: Au, H}_2\text{O.}\quad\text{Mixtures: salt water, air.}
Classification of matter starts with distinguishing pure substances from mixtures. Pure substances have uniform and definite composition throughout.

Example 2

medium
How can you determine whether a clear liquid is a pure substance or a mixture?

Practice Problems

Try these problems on your own first, then open the solution to compare your method.

Example 1

easy
Is orange juice a pure substance or a mixture? Explain.

Example 2

hard
Both distilled water and steel are uniform in appearance and properties. Explain why distilled water is classified as a pure substance while steel is a mixture.
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Background Knowledge

These ideas may be useful before you work through the harder examples.

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