concentration

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concentration,

in chemistry, measure of the relative proportions of two or more quantities in a mixturemixture,
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.
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. 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 equilibriumchemical equilibrium,
state of balance in which two opposing reversible chemical reactions proceed at constant equal rates with no net change in the system. For example, when hydrogen gas, H2, and iodine gas, I2
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).

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 solutionssolution,
in chemistry, homogeneous mixture of two or more substances. The dissolving medium is called the solvent, and the dissolved material is called the solute. A solution is distinct from a colloid or a suspension.
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: 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 molesmole,
in chemistry, a quantity of particles of any type equal to Avogadro's number, or 6.02×1023 particles. One gram-molecular weight of any molecular substance contains exactly one mole of molecules.
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 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 neutralizationneutralization,
chemical reaction, according to the Arrhenius theory of acids and bases, in which a water solution of acid is mixed with a water solution of base to form a salt and water; this reaction is complete only if the resulting solution has neither acidic nor basic
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 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 weightequivalent weight.
The equivalent weight of an element or radical is equal to its atomic weight or formula weight divided by the valence it assumes in compounds. The unit of equivalent weight is the atomic mass unit; the amount of a substance in grams numerically equal to the
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); e.g., a solution containing 49.04 grams (one gram-equivalent weight) of sulfuric acid, H2SO4, 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.

concentration

The diameter of the telescopic image of a point-source of light, such as a star. The image is increased from point size by unavoidable optical effects in the telescope, specifically diffraction (see Airy disk), and for ground-based telescopes it is further increased by distortion due to atmospheric conditions at the time of observation, i.e. by the seeing.

Concentration

 

in chemistry, the value representing the relative quantity of a given component (independent constituent) in a physicochemical system (mixture, solution, melt). The most commonly used methods of expressing concentration are (1) mass fraction—the ratio of the mass of the given component to the mass of the entire system; this ratio multiplied by 100 yields the concentration in weight percent; (2) atomic, or mole, fraction—the ratio of the number of gram atoms (moles) of a given component to the total number of gram atoms (moles) of the system; this ratio multiplied by 100 yields the concentration in atom (mole) percent; and (3) volume fraction—the ratio of the volume of the given component to the total volume of the system; this ratio multiplied by 100 yields the concentration in volume percent.

The concentration of liquid systems is often expressed by the weight of the substance dissolved in 100 g (sometimes in 1 l) of solvent or by the number of moles of substance per 1,000 moles of solvent. In the study of solutions, the concepts of molarity (the number of moles of solute per 1 l of solvent) and molality (the number of moles of solute per 1,000 grams of solvent) are often used. In volumetric analysis, the concentration is expressed by normality (the number of gram equivalents of the active constituent per 1 l of solution) and by titer (the number of grams of active substance or the substance being determined per 1 ml of solution).

In practice, concentration is determined using both the standard methods of quantitative analysis and certain instrumental methods, which make it possible to perform rapid and sufficiently accurate calculations of the content of the main component (for example, determination of the concentration of aqueous solutions of acids, alkalis, salts, and ethyl alcohol by measuring density with the aid of a hydrometer).

REFERENCES

Anosov, V. Ia, and S. A. Pogodin. Osnovnye nachalafizikokhimicheskogo analiza. Moscow-Leningrad, 1947. Pages 81–83.
Terminologiia termodinamiki; sborniki rekomenduemykh terminov, fasc. 7. Edited by A. M. Terpigorev. Moscow, 1952.
Kireev, V. A. Kurs fizicheskoi khimii. Moscow, 1955. Pages 340–44.
Vinogradov, G. V. Nomogrammy perescheta kontsentratsii. Moscow-Leningrad, 1948.

S. A. POGODIN

concentration

[‚kän·sən′trā·shən]
(chemistry)
In solutions, the mass, volume, or number of moles of solute present in proportion to the amount of solvent or total solution.
(hydrology)
The ratio of the area of the sea covered by ice to the total area of sea surface.
(mathematics)
An operation that provides a relatively sharp boundary to a fuzzy set; for a fuzzy set A with membership function mA, a concentration of A is a fuzzy set whose membership function has the value [mA (x)]αfor every element x, where α is a fixed number that is greater than 1.
(mining engineering)
Separation and accumulation of economic minerals from gangue.

concentration

1. Chemistry the strength of a solution, esp the amount of dissolved substance in a given volume of solvent, usually expressed in moles per cubic metre or cubic decimetre (litre).
2. Economics the degree to which the output or employment in an industry is accounted for by only a few firms
3. another name (esp US) for Pelmanism

concentration

In communications, the combining of multiple channels into one.
References in periodicals archive ?
We conducted complete blood count for various hematological values like hemoglobin (Hgb), erythrocyte sedimentation rate (ESR), red blood cell (RBC), hematocrit (HCT), packed cell volume (MCV), mean corpuscular hemoglobin (MCH), mean corpuscular hemoglobin concentration (MCHC), red cell distribution width (RDW), mean platelet volume (MPV), platelet, white blood cell (WBC), neutrophil, lymphocyte, eosinophil, and monocytes.
Mean corpuscular hemoglobin concentration,###30.93 +- 5.24###27.5 +- 0.71###27.76 +- 0.65
Qualitative critical results for children2 include the following: For hematology--presence of blasts in the blood smear; new diagnosis orfindings of leukemia; presence of drepanocytes (sickle cells); atypical lymphocytes, or abnormal reticulocyte count; abnormal erythrocyte indices (mean corpuscular volume, mean corpuscular hemoglobin, mean corpuscular hemoglobin concentration).
Table 6: MEAN CORPUSCULAR HEMOGLOBIN CONCENTRATION (MCHC) Male Female N 39 61 Mean 35 32 SD 3.26 4.30 Table 6 shows a statistically highly significant difference (p<0.001) in the MCHC of males and females.
Though MCHC is the parameter that reflects mean corpuscular hemoglobin concentration of individual red blood cell, report from previous studies has shown that MCHC showed the least change but the use of MCHC is limited to only in quality control purpose more than in diagnostic purpose [6].
Hematologic results (mean [SD]) were erythrocytes 3.6 [+ or -] 0.5 x [10.sup.6] cells/[mm.sup.3], hemoglobin level 12.8 [+ or -] 1.4 g/dL, packed cell volume 46% [+ or -] 3.8%, mean corpuscular volume 132 [+ or -] 20 fL, mean corpuscular hemoglobin (MCH) 36 [+ or -] 5.7 pg, mean corpuscular hemoglobin concentration (MCHC) 28% [+ or -] 3.5%, thrombocytes 26.3 [+ or -] 9.3 x [10.sup.3] cells/[mm.sup.3], leukocytes 11.9 [+ or -] 4.5 x [10.sup.3]cells/[mm.sup.3], heterophils 6284 [+ or -] 2715 cells/[mm.sup.3], lymphocytes 5473 [+ or -] 2408 cells/[mm.sup.3], monocytes 113 [+ or -] 162 cells/[mm.sup.3], eosinophils 10 [+ or -] 42 cells/[mm.sup.3] basophils 27 [+ or -] 64 cells/[mm.sup.3].
During the slow phase, the RBC moves generally along the mean corpuscular hemoglobin concentration line, and the rate of progression is quantified by a.
At the laboratory, blood samples were rendered to hematological analysis included packed cell volume (PCV), total erythrocyte count (TEC), hemoglobin (Hb) concentration and red cell indices, mean corpuscular volume (MCV), mean corpuscular hemoglobin (MCH), mean corpuscular hemoglobin concentration (MCHC), total leukocyte count (TLC) and ratio of TEC/TLC (Linne and Ringsurd, 1999).
Mean values of Hb, mean corpuscular volume (MCV), mean corpuscular hemoglobin (MCH), and mean corpuscular hemoglobin concentration (MCHC) among students with sickle cell trait were higher than those with [beta]-thalassemia.
Qualitative critical results for children2 include the following: For hematology-presence of blasts in the biood smear; new diagnosis or findings of leukemia; presence of drepanocytes (sickle cells); atypical lymphocytes, or abnormal reticulocyte count; abnormal erythrocyte indices (mean corpuscular volume, mean corpuscular hemoglobin, mean corpuscular hemoglobin concentration).
In addition, significant age-related differences were noted in red and white blood cell counts, packed cell volume, hemoglobin concentration, mean corpuscular volume, mean corpuscular hemoglobin concentration, fibrinogen level, and heterophils, lymphocytes, and eosinophils (P < .005).

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