Mixture
In chemistry, a mixture is a substance made by combining two or more different materials in such a way that no chemical reaction occurs. The objects do not bond together in a mixture. A mixture can usually be separated back into its original components. Some examples of Mixtures are oil, ocean water and soil. Mixtures are the product of a mechanical blending or mixing of chemical substances like elements and compounds, without chemical bonding or other chemical change, so that each ingredient substance retains its own chemical properties and makeup. [1]
While there are no chemical changes in a mixture, physical properties of a mixture, such as its melting point, may differ from those of its components. Mixtures can usually be separated by any mechanical means.
There are three different types of mixtures, homogeneous mixtures (also called solutions), heterogeneous mixtures, and colloidal dispersions.
Homogeneous mixtures
Homogeneous mixtures are mixtures that have definite, true composition and properties. Particles are uniformly spread. For example, any amount of a given mixture has the same composition and properties. Examples are solutions and some alloys (but not all). A homogeneous mixture is a uniform mixture consisting of only one phase. Examples are gasoline and margarine.
Solutions
A solution is a homogeneous mixture of two or more substances (the solutes) [[dissolve|dissolved in another substance (the solvent). Solutions have all particles within the size of atoms, small molecules or small ions, less than 1nm in all dimensions [2]. A common example would be a solid dissolving into a liquid (i.e. salt or sugar dissolving in water or gold into mercury). Liquids dissolve into one another, and sometimes liquids dissolve into gases, for example water vapor and the atmosphere. Common examples include soft drinks, where carbon dioxide is trapped in the liquid through carbonation. Several solution properties collectively called colligative properties change as a function of solute concentration. Solubility is a compound property.
Colloidal dispersions
A homogeneous mixture in which the particles of one or more components have at least one dimension in the range of 1 to 1000nm, larger than those in a solution but smaller than those in a suspension. [2] In general, a colloid or colloidal dispersion is a substance with components of one or two phases, a type of mixture intermediate between a homogeneous mixture and a heterogeneous mixture with properties also intermediate between the two. A colloid will not settle if left to sit. Examples of this are jelly and glue.
Heterogeneous mixtures
Heterogeneous mixtures are mixtures with indefinite composition, for example, granite. Salad is a typical example of this kind of mixture. Heterogeneous mixtures are said to have several phases (not to be confused with phases of matter). The parts of a heterogeneous composition can be mechanically separated from each other. Examples include salad and trail mix.
Suspensions
A heterogeneous mixture in which the particles, of at least one component is larger than 1μm (1000nm) in at least one dimension, larger than colloidal particles. [2] Unlike colloids, suspensions will eventually settle. An example of a suspension would be sand in water. Particles of suspensions exhibit the Tyndall effect, that is, they are big enough to disperse light, like colloids.
See also
- Colligative properties
- Molar solution
- Percentage solution
- Separation process
- Solubility
- Solubility equilibrium
- Suspension (chemistry)
Notes
- ↑ P W Atkins, and Julio De Paula. Atkins' Physical chemistry. 7th Edition. (New York: Oxford University Press, 2002, ISBN 0198792859)
- ↑ 2.0 2.1 2.2 James E Brady, and Frederick Senese. Chemistry : matter and its changes. 4th Edition. (NJ: Wiley, 2004, ISBN 0471215171)
External links
- IUPAC Gold Book Definition - Retrieved November 9, 2007.
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