Pure Substances and Mixtures
Pure substances have fixed composition; mixtures can vary.
About this topic
A pure substance, an element or compound, has fixed composition and properties, such as distilled water or gold. A mixture contains two or more substances physically combined in any proportion, each keeping its own properties. Mixtures may be homogeneous (uniform, like salt water) or heterogeneous (visibly different parts, like sand and water).
Purity can be tested by melting or boiling point: a pure substance melts and boils at one sharp temperature, while a mixture melts over a range and at a different temperature than its parts. This is why salt is spread on icy roads; the salt makes a mixture that melts below zero degrees Celsius. Homogeneous mixtures are also called solutions, and alloys such as brass are solid solutions.
Think of a bowl of trail mix: you can see and pick out the nuts, raisins and chocolate, and you could make the mix with more or less of each. Compare that with a compound such as water, always two hydrogen atoms to one oxygen, which cannot be pulled apart by hand. Air, seawater, soil and blood are mixtures; oxygen, salt and sugar are pure.
A common error is calling clean-looking tap water or fresh air pure. In chemistry, pure means one substance only. Another is thinking mixing makes a new substance; in a mixture, no chemical reaction occurs.
Key ideas
- Elements and compounds are pure
- Homogeneous mixtures look uniform
- Separate mixtures by physical means
Quick check
Use cases: where Pure Substances and Mixtures helps
- Homework: review the key idea behind Pure Substances and Mixtures before you start a problem set.
- Exam revision: use the quick check to test whether you can recall Pure Substances and Mixtures without notes.
- Visual learning: play with the interactive lab to see how Pure Substances and Mixtures changes when you adjust its inputs.
- Teaching a friend: explain Pure Substances and Mixtures in your own words, then compare your version with the key ideas.
Chemistry explains medicine, food, cleaning products, fuels and building materials.
Frequently asked questions
What is Pure Substances and Mixtures?
Pure substances have fixed composition; mixtures can vary.
What will I learn in Pure Substances and Mixtures?
Elements and compounds are pure. Homogeneous mixtures look uniform. Separate mixtures by physical means.
Is Pure Substances and Mixtures part of Chemistry?
Yes. It is one of 150 Chemistry topics on LearnViz HighSchoolEdu, with 3 key ideas, a live animation and a quick check.
Does the Pure Substances and Mixtures lab work on a phone or tablet?
Yes. The animation resizes to fit your screen and supports touch, so you can drag, tap and slide with your finger.
How should I study Pure Substances and Mixtures?
Read the summary and key ideas first, play with the interactive lab to see the idea in motion, then answer the quick check. If you get a question wrong, go back to the key idea it tests.
Do I need an account, and is my progress saved?
No account is needed. Marking a topic as learned is saved in your own browser, so it stays on that device and is not sent to a server.