Mixture

For other uses, see Mixture (disambiguation).

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A mixture is a chemical material of variable composition that contains two or more substances.

A mixture is a chemical substance which is a homogeneous or heterogeneous association without chemical bonding of elements and/or compounds in varying proportions and that retain their own individual properties and makeup. Mixtures can usually be separated by mechanical means.

There are no chemical changes in a mixture, i.e., each substance in a mixture keeps the same chemical properties and makeup as before. Physical properties of mixtures, e.g., the melting point, may considerably differ from those of its components. It usually does not.

Types of mixtures

• Homogeneous mixtures are mixtures that have a definite composition and properties, i.e., any amount of a given mixture has the same composition and properties. Examples are solutions and some alloys (but not all).

• Heterogeneous mixtures are mixtures without definite composition, for example, granite. Pizza is a typical humorous example of this kind of mixture. Heterogeneous mixtures are said to have several phases (not to be confused with phases of matter), i.e., parts of homogeneous composition that can be mechanically separated from the rest.

Solutions

One type of a homogeneous mixture is a solution. In chemistry, a solution is a homogeneous mixture of one or more substances (the solutes) dissolved in another substance (the solvent). A common example would be a solid dissolving into a liquid, like salt or sugar dissolving in water (or even gold into mercury, forming an amalgam); but also gases may dissolve into liquids, like carbon dioxide or oxygen in water, and liquids and gases into themselves.

An ideal solution is one where the interactions of the molecules of the solvent with each other are equal to their interactions with the solutes. The properties of an ideal solution can be calculated by the linear combination of the properties of its components.

The solvent is conventionally defined as the substance that exists in a greater quantity than the solute(s) in the solution. If both solute and solvent exist in equal quantities (such as in a 50% ethanol 50% water solution), the concepts of "solute" and "solvent" become less relevant, but the substance that is more often used as a solvent is normally designated as the solvent (in this case, water).

Solvents can be broadly classified into polar and non-polar solvents. Common polar solvents include water and ethanol. Ethanol (C2H5OH) and other alcohols can be considered both polar and nonpolar as the OH end is polar (attracts polar molecules) and the hydrocarbon end is nonpolar (attracts nonpolar molecules). Generally polar or ionic compounds will only dissolve in polar solvents. A simple test for the polarity of a liquid solvent is to rub a plastic rod, to induce static electricity. Then hold this charged rod close to a running stream of the solvent. If the path of the solvent deviates when the rod is held close to it, it is a polar solvent.

When a solute is dissolved into a solvent, especially polar solvents, a structure forms around it (a process called solvation), which allows the solute-solvent interaction to remain stable.

When no more of a solute can be dissolved into a solvent, the solution is said to be saturated. However the point at which a solution can become saturated changes significantly with different environmental factors, such as temperature, pressure, and contamination. Raising the solubility (such as by increasing the temperature) to dissolve more solute, and then lowering the solubility causes a solution to become supersaturated.

In general the greater the temperature of a solvent, the more of a given solute it can dissolve. However, some compounds exhibit reverse solubility, which means that as a solvent gets warmer, less solute can be dissolved. Some surfactants exhibit this behaviour.

There are several ways to measure the strength of a solution; see concentration for more information.

There are many types of solutions: Examples of solutions Solute Gas Liquid Solid Solvent Gas Oxygen and other gases in nitrogen (air) Water vapor in air (humidity) The odor of a solid results from molecules of that solid being dissolved in the air Liquid Carbon dioxide in water (carbonated water) Ethanol (common alcohol) in water; various hydrocarbons in each other (petroleum) Sucrose (table sugar) in water; sodium chloride (table salt) in water Solid Hydrogen dissolves rather well in metals; platinum has been studied as a storage medium Water in activated charcoal; moisture in wood Steel, duralumin, other metal alloys [edit]

See also

   * Colligative properties
   * Colloid
   * Making up solutions
   * Molar solution
   * Percentage solution
   * Solubility equilibrium
   * Soluble
   * Suspension (chemistry)

See also

• Separation of mixtures