Mixtures
A mixture is made from different substances that are not chemically joined.
For example, powdered iron and powdered sulfur mixed together make a mixture of iron and sulfur. They can be separated from each other without a chemical reaction, in the way that different coloured sweets can be picked out from a mixed packet and put into separate piles.
There are times when the purity of a substance is very important. For example, a medicine must not contain any harmful chemicals.
Mixtures and compounds
Mixtures have different properties from A substance formed by the chemical union of two or more elements.. The table summarises these differences.
| Mixture | Compound | |
| Composition | Variable composition 鈥 you can vary the amount of each substance in a mixture | Definite composition 鈥 you cannot vary the amount of each element in a compound |
| Joined or not | The different substances are not chemically joined together | The different elements are chemically joined together |
| Properties | Each substance in the mixture keeps its own properties | The compound has properties which are different from the elements it contains |
| Separation | Each substance is easily separated from the mixture | It can only be separated into its elements using chemical reactions |
| Examples | Air, seawater, most rocks | Water, carbon dioxide, magnesium oxide, sodium chloride |
| Composition | |
|---|---|
| Mixture | Variable composition 鈥 you can vary the amount of each substance in a mixture |
| Compound | Definite composition 鈥 you cannot vary the amount of each element in a compound |
| Joined or not | |
|---|---|
| Mixture | The different substances are not chemically joined together |
| Compound | The different elements are chemically joined together |
| Properties | |
|---|---|
| Mixture | Each substance in the mixture keeps its own properties |
| Compound | The compound has properties which are different from the elements it contains |
| Separation | |
|---|---|
| Mixture | Each substance is easily separated from the mixture |
| Compound | It can only be separated into its elements using chemical reactions |
| Examples | |
|---|---|
| Mixture | Air, seawater, most rocks |
| Compound | Water, carbon dioxide, magnesium oxide, sodium chloride |
An example 鈥 iron, sulfur and iron sulfide
Iron and sulfur react together when they are heated to make a compound called iron sulfide.
Here are some of the differences between a mixture of iron and sulfur, and iron sulfide:
- the mixture can contain more or less iron, but iron sulfide always contains equal amounts of iron and sulfur
- the iron and sulfur All elements are made of atoms. An atom consists of a nucleus containing protons and neutrons, surrounded by electrons. are not joined together in the mixture, but they are joined together in iron sulfide
- the iron and sulfur still behave like iron and sulfur in the mixture, but iron sulfide has different properties from both iron and sulfur
- you can separate the iron from the mixture using a magnet, but this does not work for iron sulfide