Summary
Not all matter is pure. Many things are mixtures: two or more substances together that do not react and keep their properties, like salt water or air. In a homogeneous mixture the components cannot be told apart by eye (sugar water, steel); in a heterogeneous one they can (oil and water, a salad).
Because the components of a mixture are not chemically joined, they can be separated by physical methods, choosing the one that uses a difference between them. Filtration separates a solid from a liquid (straining coffee); decanting separates two liquids that do not mix or a solid that settles; evaporation leaves the dissolved solid behind when the liquid goes (salt from seawater); and distillation separates liquids by their boiling point.
Key points
- A mixture is two or more substances together that keep their properties.
- Homogeneous: components not visible (sugar water). Heterogeneous: visible (oil and water).
- The components of a mixture are separated by physical methods.
- Filtration: separates a solid from a liquid (straining).
- Decanting: separates liquids that do not mix or a solid that settles.
- Evaporation: the liquid leaves and the dissolved solid remains (salt).
- Distillation: separates liquids by their boiling point.