A mixture of iron and sulpher. Image credit MediaWiki
ZIMSEC O Level Combined Science Notes: Mixtures and compounds
- When two or more elements are brought together they may either form:
- a compound
- or a mixture
- The table below shows the differences between a compound and a mixture
| Mixture | Compound |
|---|---|
| Is formed by a physical change | Is formed by a chemical change |
| The components of the mixture can be separated easily by physical changes/means e.g. using a magnet or sieve | The parts of the compound cannot be separated by physical means such as using a sieve |
| The mixture has the properties of the added substances for example iron fillings are still magnetic | The properties of the compound are different from those of the original reagents |
| They are neither endothermic nor exothermic | They are usually either endothermic or exothermic |
| No new substance is formed | A new substance is formed |
- An example of a compound and a mixture can be demonstrated using iron fillings and sulphur
- If the two are mixed they form a mixture
- In the mixture the iron which is black and magnetic retains its properties
- The sulphur which is a yellow solid retains its solid
- Sulphur dissolves in toluene
- The mixture can be separated by
- physically picking out the iron fillings
- picking them using a magnet
- Pouring toluene on the mixture and filtering it since the iron fillings will not be able to pass through the filter
- If however the mixture is heated in a test tube
- A new substance known as iron sulphide is formed
- This substance is a compound
- You cannot see the iron fillings or the powdered sulphur
- A exothermic chemical reaction occurs and a new compound is formed
- Heat is given out even when the burner is removed
- The mixture continues to glow due to the chemical reaction
- The resultant compound is not magnetic
- The mixture changes colour and the ingredient elements can no longer be observed
To access more topics go to the Combined Science Notes page.
