concentration in chemistry

From Big Medical Encyclopedia

CONCENTRATION in chemistry — the size characterizing abundance of this component in mix or in solution. The concept «concentration of substances in biol, systems» extends not only to solutions, i.e. on biol, liquids, but also to cells and fabrics which can be considered as mixes of substances. Deviations To. substances in biol, liquids and fabrics from norm serve one of indicators patol, the changes happening in an organism. Definition of these To. the wedge, biochemistry enters a task. Constancy To. metabolites in an organism — one of manifestations homeostasis (see). Constancy belongs to classical examples To. sodium chloride in blood. To. substances consider at a dosage of medicines. On measurement To. the quantitative characteristic of components of the environment is based.

Measurement To. substances directly in biol, structures it is carried out gistokhy, or isotope methods. However mostly To. substances is defined in the tests received after homogenization of fabrics (see. Homogenates ) and extractions (see). For this purpose use as classical methods: weight (gravimetric), the caption also mt ri chesky and so forth, and spektrofotometriya (see), the fluorescent analysis (see. Fluorescence ), conductometry (see), radioactivity measurement (see. Autoradiography ), enzymatic and biol, methods. Biol, methods assume use of the isolated bodies or test cultures of microorganisms for definition To. hormones, vitamins and antibiotics. If in complex mixtures of biogenic connections it is impossible to define To. individual substances, define, e.g., To. organic phosphate, general nitrogen etc.

There are three main principles of expression K. Pervy is based on weight units (micrograms, milligrams, grams and kilograms). The second — on atomic, molecular, equivalent and ionic units (a gram atom, mol, gram equivalent, gram ion). The third is based on volume units (micro liters, milliliters, liters). It is possible to express quantities of this component and all mix in identical units or to use the mixed ways of expression of K. V medico-biol. researches most often apply the next ways.

Weight percentage on weight (weight. the % or and %) is expressed by number of mass units (e.g., the number of the grams of substance dissolved in 100 units of weight, napr, by of solution); 100 g of 0,9% of solution of sodium chloride (fiziol. solution) 99,1 g of water and 0,9 g of NaCl contain. To. the diluted solutions express number of milligrams of solute in 100 g of solution or in milligram-percent (amg %). E.g., is normal To. cholesterol of plasma makes 100 — 250 mg of %. An outdated way of expression To. in per mille (and ‰) the number of mass units of solute on 1000 units of mass of solution means.

Percentage on volume (about. the % or v of %) specifies how many volumes of substance are the share of 100 volumes of solution or mix. E.g., the air exhaled by lungs contains 16,4% of oxygen and 4,1% of carbon dioxide on volume.

Molar concentration (molarity of solution, M) is expressed by number of moths of solute (see. Molecular weight ), contained in 1 l of solution. One-molar call the solution having To., equal 1 M. The solutions having To. 0,1, 0,01 and 0,001 M, call respectively detsi-, santi-and millimolar. E.g., for preparation of 1 l 0,4 M of solution of sucrose its hinge plate equal 0,4 asking sucrose, i.e. 0,4 • 342,3 g, transfer to a volumetric flask on 1 l and bring solvent to a tag. Earlier in certain cases used ponyaty «molal concentration» (number of moths of solute in 1000 of solvent).

Osmomolyarny concentration. One osmomol equals to amount of substance in 1 l of solution creating in it at 0 ° osmotic pressure (see), equal 22,4 atm. Big molecules create rather small osmotic pressure. Proteins of a blood plasma, e.g., contain in number of 7 g in 100 ml (on average), their pier. the weight (weight) equals 70 000 — 1 000 000, and they cause the osmotic pressure equal only 2 milliosmomolyam on 1 l. For not dissociating substances of the concept «mol» and «osmomol» match. At the same time 1 M solution of NaCl which is completely dissociating on ions creates the osmotic pressure equal of 44,8 atm in 1 l, and contains 2 osmomolya.

Normal concentration (a normality of solution, N) is expressed by number of grams equivalents of solute,-ekv (see. Equivalent chemical ), contained in 1 l of solution. Along with names one - and two-normal solution use names detsi-, santi-and millinormalny solution.

The caption of solution (T) is a number of grams of solute in 1 ml of solution. E.g., the caption of solution of caustic soda equal 0,04, means that 1 ml of solution contains 0,04 g of NaOH. The caption and a normality use for expression To. in titrimetric analysis (see).

Put also such qualitative characteristics into practice To. solutions, as «diluted» and «concentrated». To. some connections can be determined by their activity. To. the radioisotopes which are widely applied in a medico-biol. researches, express in curie or in impulses in unit of time per unit mass or the volume of substance. In some biochemical, researches K. radioactive ATP, e.g., marked on trailer phosphate, makes 1000 imp/min/mg, and annual average admissible To. 60Co in water of open reservoirs 3,5*10 equals - 8 curie/l. To. enzymes in fabrics or extracts it is possible to express number of specific activity units per unit mass or volume; e.g., activity of ribonuclease in a muscle of a ventricle of heart normal equals 101 pieces/g.

Bibliography: Biochemical methods of a research in clinic, under the editorship of A. A. Pokrovsky, page 392, M., 1969; Goronovsky I. T., Nazarenko Yu. P. and E. F Nekryach. Short reference book on chemistry, Kiev, 1974.

E. V. Ramensky.