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concentration

concentration

The Columbia Encyclopedia, 6th ed. | 2011 | Copyright

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 determines the rates of reactions and the conditions at equilibrium (see chemical equilibrium ).

Concentration may be expressed in a number of ways. The simplest statement of the concentrations of the components of a mixture is in terms of their percentages by weight or volume. Mixtures of solids or liquids are frequently specified by weight percentage concentrations, such as alloys of metals or mixtures used in cooking, whereas mixtures of gases are usually specified by volume percentages. Very low concentrations may be expressed in parts per million (ppm), as in specifying the relative presence of various substances in the atmosphere.

In addition to these means of expressing concentration, several others are defined especially for describing solutions : molarity, molality, mole fraction, formality, and normality. Some of these define the concentration of the solute in reference to the amount of solvent, others in reference to the total amount of solution. The molarity of a solution is the number of moles of solute per liter of solution; e.g., a solution of glucose in water containing 180.16 grams (1 gram-molecular weight, or mole) of glucose per liter of solution is referred to as one molar (1 M ). The molality of a solution is the number of moles of solute per 1,000 grams of solvent; a solution prepared by dissolving 180.16 grams of glucose in 1,000 grams of water is one molal (1 m ). The mole fraction of a solution is the ratio of moles of solute to the total number of moles in the solution. Since ionic compounds, such as sodium chloride, NaCl, do not occur as molecules, their concentrations cannot be expressed in terms of molarity, molality, or mole fraction. Instead, the concentration of an ionic compound in solution may be given by its formality, the number of gram-formula weights of the compound per liter of solution; e.g., a solution containing 58.44 grams (one gram-formula weight) of NaCl per liter of solution is one formal (1 F ). In considering the reactions of certain solutions in combination, for example the neutralization of acids and bases, a useful expression of the concentration is the normality of each solution, the number of gram-equivalent weights of solute per liter of solution (see equivalent weight ); e.g., a solution containing 49.04 grams (one gram-equivalent weight) of sulfuric acid, H 2 SO 4 , per liter of solution is one normal (1 N ). Concentrations of solutions may also frequently be given in terms of the weight of solute in a given volume of solvent or solution.

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concentration

The Oxford Pocket Dictionary of Current English | 2009 | Copyright

con·cen·tra·tion / ˌkänsənˈtrāshən/ • n. 1. the action or power of focusing one's attention or mental effort. ∎  (concentration on/upon) dealing with one particular thing above all others: concentration on the needs of the young can mean that the elderly are forgotten. 2. a close gathering of people or things: the largest concentration of Canada geese on earth. ∎  the action of gathering together closely: the concentration of power . 3. the relative amount of a given substance contained within a solution or in a particular volume of space; the amount of solute per unit volume of solution: the gas can collect in dangerous concentrations. ∎  the action of strengthening a solution by the removal of water or other diluting agent or by the selective accumulation of atoms or molecules.

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concentration

A Dictionary of Biology | 2004 | Copyright

concentration The quantity of dissolved substance per unit quantity of solvent in a solution. Concentration is measured in various ways. The amount of substance dissolved per unit volume (symbol c) has units of mol dm–3 or mol l–1. It is now called `concentration' (formerly molarity). The mass concentration (symbol ρ) is the mass of solute per unit volume of solvent. It has units of kg dm–3, g cm–3, etc. The molal concentration (or molality; symbol m) is the amount of substance per unit mass of solvent, commonly given in units of mol kg–1.
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concentration

A Dictionary of Earth Sciences | 1999 | | Copyright

concentration
1. In chemistry, the number of molecules or ions in a given volume of a substance, expressed as moles of solute per litre of solution (molarity).

2. In mineral processing, the production of a concentrate from its ore, or the process of increasing concentration by evaporation, etc.
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AILSA ALLABY and MICHAEL ALLABY. "concentration." A Dictionary of Earth Sciences. 1999. Encyclopedia.com. 26 May. 2012 <http://www.encyclopedia.com>.

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Concentration

Dictionary of Collective Nouns and Group Terms | 1985 | Copyright

Concentration

a concentrated collection or mass; a distillate.

Examples: concentration of broken beams, 1634; of lunar beams, 1691; of related species, 1881; of hostile tribes, 1841; of forces, 1804.
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concentration

The Oxford Essential Dictionary of the U.S. Military | 2001 | Copyright

concentration n.
1. an assembly of troops in a given area.

2. the simultaneous firing of a number of artillery pieces or mortars on a common, usually prearranged, area or target.
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concentration

A Dictionary of Business and Management | 2006 | Copyright

concentration The degree to which an industry is dominated by a small group of firms and thus closed to competitive pressure.
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