Mixture facts for kids
In chemistry, a mixture is a substance that is made up of two or more simpler substances. These substances can be chemical elements or compounds. A mixture can be made of liquids, solids, or gases.
A mixture is not the same as a compound which is made of two or more atoms connected together. For instance, a mixture of the gases hydrogen and nitrogen contains hydrogen and nitrogen, not the compound ammonia which is made of hydrogen and nitrogen atoms.
A mixture where the different parts can be distinguished easily is called heterogenous, one where this is not the case is called homogeneous. A third form is called colloid.
If one substance in a mixture dissolves in the other, it is called a solution. For example, if sugar is put in water it forms a mixture, then dissolves to make a solution. If it does not dissolve, it would be called a suspension.
Solids can be mixtures also. Alloys are mixtures. Many kinds of soil and rock are mixtures of different minerals. Thus, a mixture is made of two or more elements and/or compounds which are not chemically combined.
Characteristics of mixtures
All mixtures can be characterized as being separable by mechanical means (e.g. purification, distillation, electrolysis, chromatography, heat, filtration, gravitational sorting, centrifugation). Mixtures differ from chemical compounds in the following ways:
- The substances in a mixture can be separated using physical methods such as filtration, freezing, and distillation.
- There is little or no energy change when a mixture forms (see Enthalpy of mixing).
- The substances in a mixture keep their separate properties.
In the example of sand and water, neither one of the two substances changed in any way when they are mixed. Although the sand is in the water it still keeps the same properties that it had when it was outside the water.
- mixtures have variable compositions, while compounds have a fixed, definite formula.
- when mixed, individual substances keep their properties in a mixture, while if they form a compound their properties can change.
The following table shows the main properties and examples for all possible phase combinations of the three "families" of mixtures :
| Dispersion medium (mixture phase) | Dissolved or dispersed phase | Solution | Colloid | Suspension (coarse dispersion) |
|---|---|---|---|---|
| Gas | Gas | Gas mixture: air (oxygen and other gases in nitrogen) | None | None |
| Liquid | None | Liquid aerosol: fog, mist, vapor, hair sprays |
Spray | |
| Solid | None | Solid aerosol: smoke, ice cloud, air particulates |
Dust | |
| Liquid | Gas | Solution: oxygen in water |
Liquid foam: whipped cream, shaving cream |
Sea foam, beer head |
| Liquid | Solution: alcoholic beverages |
Emulsion: milk, mayonnaise, hand cream |
Vinaigrette | |
| Solid | Solution: sugar in water |
Liquid sol: pigmented ink, blood |
Suspension: mud (soil particles suspended in water), chalk powder suspended in water |
|
| Solid | Gas | Solution: hydrogen in metals |
Solid foam: aerogel, styrofoam, pumice |
Foam: dry sponge |
| Liquid | Solution: amalgam (mercury in gold), hexane in paraffin wax |
Gel: agar, gelatin, silicagel, opal |
Wet sponge | |
| Solid | Solution: alloys, plasticizers in plastics |
Solid sol: cranberry glass |
Clay, silt, sand, gravel, granite |
Gallery
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Red wine in a glass, a homogeneous mixture.
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Different kinds of peppercorn, a heterogenoeus mixture
See also
In Spanish: Mezcla para niños
