solution, in chemistry, homogeneous mixture mixture, in chemistry, a physical combination of two or more pure substances (i.e., elements or compounds). A mixture is distinguished from a compound, which is formed by the chemical combination of two or more pure substances in a fixed, definite proportion.
..... Click the link for more information. of two or more substances. The dissolving medium is called the solvent solvent, constituent of a solution that acts as a dissolving agent. In solutions of solids or gases in a liquid, the liquid is the solvent. In all other solutions (i.e.
..... Click the link for more information. , and the dissolved material is called the solute. A solution is distinct from a colloid colloid (kŏl`oid) [Gr.,=gluelike], a mixture in which one substance is divided into minute particles (called colloidal particles) and
..... Click the link for more information. or a suspension suspension, in chemistry, mixture of two substances, one of which is finely divided and dispersed in the other. Common suspensions include sand in water, fine soot or dust in air, and droplets of oil in air. A suspension is different from a colloid or solution .
..... Click the link for more information. .

In most common solutions, the solvent is a liquid, often water, and the solute may be a solid, gas, or liquid. For example, syrups are solutions of sugar, a solid, in water, a liquid; household ammonia is a solution of ammonia gas in water; and vinegar is a solution of acetic acid, a liquid, in water. When two liquids, e.g., water and ethanol, can be mixed in any proportions, the solvent is commonly considered to be the one present in greater proportion. Some alloys alloy (ăl`oi, əloi`) [O. Fr.
..... Click the link for more information. are solutions of one solid in another, as are many rocks. A mixture of gases, such as air, is usually not thought of as a solution.

Characteristics of Solutions

The solute particles in a solution are generally of molecular size or smaller, much smaller than those in a colloid or a suspension. The solute particles cannot be observed even with an ultramicroscope. They do not settle out from the solvent on standing, and they cannot be separated from the solvent by physical means, such as filtration or centrifugation. On the other hand, a solution differs from a compound compound, in chemistry, a substance composed of atoms of two or more elements in chemical combination, occurring in a fixed, definite proportion and arranged in a fixed, definite structure. A compound is often represented by its chemical formula .
..... Click the link for more information. in that its components can occur in continuously varying proportions, within certain limits (although within a given solution they are present in the same proportions throughout the solution), while the components of a compound can occur only in certain fixed proportions.

The addition of solute affects the boiling point, freezing point, and vapor pressure of the solution, in general raising the boiling point, depressing the freezing point, and lowering the vapor pressure (see Raoult's law Raoult's law (rälz`) [for F. M.
..... Click the link for more information. ). A number of substances (acids, bases, and salts) exhibit characteristic behavior in aqueous solution. These substances dissociate in water to form positive and negative ions ion, atom or group of atoms having a net electric charge .

Positive and Negative Electric Charges

A neutral atom or group of atoms becomes an ion by gaining or losing one or more electrons or protons.
..... Click the link for more information. that enable the solution to conduct electricity. Such solutions are called electrolytic (see electrolyte electrolyte (ĭlĕk`trəlīt')
..... Click the link for more information. ).

The proportion of solute to solvent in a given solution is expressed by the concentration concentration, in chemistry, measure of the relative proportions of two or more quantities in a mixture . The concentration of a solute is very important in studying chemical reactions because it determines how often molecules collide in solution and thus indirectly
..... Click the link for more information. of the solution. Concentrations may be stated in a number of ways, such as giving the amount of solute contained in a given volume of solution or the amount dissolved in a given mass of solvent. A solution having a relatively high concentration is said to be concentrated, and a solution having a low concentration is said to be dilute.

In many solutions the concentration has a maximum limit that depends on various factors, such as temperature, pressure, and the nature of the solvent. The maximum concentration is called the solubility of the solute under those conditions. When a solution contains the maximum amount of solute, it is said to be saturated; if it contains less than that amount, it is unsaturated.

The most obvious factor affecting solubility is the nature of the solvent. Ordinary table salt (sodium chloride) is soluble in water, but only slightly soluble in ethanol, and insoluble in diethyl ether. Temperature is also important in determining solubility. Solids are usually more soluble at higher temperatures; more salt will dissolve in warm water than in an equal amount of cold water. Graphs showing the solubility of different solids as a function of temperature are called solubility curves and are very useful in chemical analysis. Solubility also depends on pressure, especially in the case of gases, which are more soluble at higher pressures.

Under certain conditions a solution may be made to contain more solute than a saturated solution at the same temperature and pressure; such a solution is called supersaturated. If even a single crystal of undissolved solute is added to a supersaturated solution, all the excess solute above the normal solubility concentration will immediately crystallize out of the solution.

Heat of Solution

The addition of some solutes to a solvent will raise the temperature of the solution, while others may lower the temperature and still others will have no noticeable effect. This behavior depends on the heat of solution of the solute in the given solvent. The heat of solution, i.e., the amount of heat given off or absorbed during the process of solution, is equal to the difference between the energy that must be supplied to break up the crystals of the solute and the energy that is released when the solute particles are taken into solution by the solvent (see enthalpy enthalpy (ĕn`thălpē)
..... Click the link for more information. ). If the heat of solution is negative (i.e., more energy is required to break up the crystal than is released in forming the solution), then the temperature will decrease; if the heat of solution is positive, the temperature will increase.

solution

In chemistry, a homogeneous mixture of two or more substances in relative amounts that can vary continuously up to the limit of solubility (saturation), if any, of one in the other. Most solutions are liquids, but solutions also can be of gases or solids—for example, air (composed primarily of oxygen and nitrogen) or brass (composed chiefly of copper and zinc; see alloy). In solutions comprising a solid dissolved in a liquid, the liquid is the solvent, and the solid is the solute; if both components are liquids, the one present in a smaller amount is usually considered the solute. If the saturation point is passed, excess solute separates out. Substances with ionic bonds (e.g., salts) and many with covalent bonds (e.g., acids, bases, alcohols) undergo dissociation into ions on dissolving and are called electrolytes. Their solutions can conduct electricity and have other properties that differ from those of nonelectrolytes. Solutions are involved in most chemical reactions, refining and purification, industrial processing, and biological processes.

See solutions.

(jargon)

solution - A marketroid term for something he wants to sell you without bothering you with the often dizzying distinctions between hardware, software, services, applications, file formats, companies, brand names and operating systems.

"Flash is a perfect image-streaming solution." "What is it?" "Um... about a thousand dollars."

See also: technology.