When two or more compounds are mixed together but not chemically combined the result is called a mixture. Unlike a pure substance (element or compound), a mixture can have variable composition. Mixtures that are evenly distributed throughout are called homogeneous. A homogeneous mixture can be an aqueous solution, such as sugar dissolved in water, a mixture of gases, or a mixture of solids such as a metal alloy. A homogenous mixture can also involve two different phases such as oxygen dissolved in water.
A heterogeneous mixture is unevenly distributed. It might have layers or chunks. Soil is an example of a heterogeneous mixture.
Mixtures can be separated without undergoing a chemical reaction because the particles that are mixed together aren't chemically bonded. Here are some ways in which mixtures are separated:
- distillation - used to separate a mixture of liquids with different boiling points
- evaporation - used to separate a soluble solid from a solvent
- filtration - used to separate a solid from a liquid
- screening - used to separate solids of different particle size such as sand and gravel
- magnetism - used to separate magnetic metals from non-metals
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