ACIDS AND BASES

From Big Medical Encyclopedia

ACIDS AND BASES — the substances capable to react acid-base interaction. Numerous To. and lakes are a part of live organisms and play a large role in vital processes. Balance To. and the lake in blood and others biol, liquids is broken at various patol, states. The quantitative indices characterizing disturbance of acid-base balance have great diagnostic value (see. Alkalosis , Acidosis , Acid-base equilibrium ). To. and the lakes which are especially concentrated have the toxic, destroying action in relation to a complete human body and its separate fabrics. By industrial production and use To. and lakes quite often represent considerable professional harm. Many pharmaceuticals are acids or the bases.

There is no uniform definition of reaction of acid-base interaction therefore there is no uniform definition of the concepts «acid» and «basis». By the end of 19 century after more than 300 years' experience with To. and lakes were empirically established the properties characterizing To. and lake as special classes of chemical connections. The most important of these properties are given in the table.

From the listed above empirical signs characterizing To. and the lake, the most general is their ability to react with each other with formation of salts and waters. This reaction called by a neutralization test and characterizing essence of acid-base interaction can be expressed by the following general equation:

HA (acid) + BOH (basis) = BA (salt) + H 2 O (water)

On this basis well-known empirical definitions were formulated To. and lake: to - you are the substances containing the hydrogen capable to be replaced with metals in the structure and reacting with the bases with formation of salts and waters; the bases are the substances containing in the structure hydroxylic (hydras oxidic) the groups capable to be replaced on the acid residues and reacting with to-tami with formation of salts and waters.

Theories of acids and the bases

there are more than ten various theories To. and lake. Below only two most standard theories, with to-rymi the physician are considered, the physiologist and the biologist should deal in practical and research activities.

The ionic theory of acids and the bases is one of the investigations of the theory of the electrolytic dissociation developed by Swedish fizikokhimiky S. Arrhenius (see. Dissociation, in chemistry , Electrolytes ). According to Arrhenius's theory, to - you are hydrogenous chemical connections which molecules in water solutions dissociate on cations of hydrogen (H + ) and anions of acid residues, and the bases are hydroxyl compounds which molecules dissociate in water on anions of a hydroxyl (OH - ) and cations of metals. E.g., dissociation salt and sulfuric to - t and the bases of potassium and barium proceeds in compliance about the equations:

>HCl — H + + Cl -  ; H 2 SO 4 —> 2H + + SO 4 2-  ;> KOH — K + + OH -  ; Ba(OH) 2 —> Ba 2+ + 2OH - .

Thus, according to S. Arrhenius, the general properties to - t are caused by presence at their solutions of ions of H + , the general properties of the bases — presence of ions of OH - , and the essence of kislotnoosnovny interaction consists in connection of ions of H + and OH - in water molecules. The neutralization test represents connection of hydrogen ions with hydroxylic ions: H + + OH - —> H 2 O, at the same time To. and lakes per se disappear. Arrhenius's theory explained many parties of chemical behavior To. and and for the first time gave to the lake the chance to quantitatively estimate their force. Sil K. and the lake is defined by sizes of their dissociation constants. So, e.g., if dissociation To. and the lake is expressed by the equations

of HA <-> H + + And - and

BOH <-> B + + OH - ,

the dissociation constant of Ka acid and a dissociation constant of the basis of Kb are equal:

Ka = [A-] • [H + ] / [HA], Kb = [In + ] • [OH - ] / [BOH]

where square brackets designated equilibrium concentrations or, more precisely, activities of the corresponding ions and molecules. The more the sizes Ka and Kb, the more force corresponding to them To. and lake. Often force To. and islands express not sizes of KA and Kb, but their negative decimal logarithms which are designated by a rka and pKb and call respectively indicators of acid and main dissociation.

However Arrhenius's theory has a number of shortcomings. It is applicable only to water solutions K. and the lake also does not extend to acid-base interactions in non-aqueous environments. To. and lakes can react with each other and being not dissociated on ions; e.g., anhydrous hydrogen chloride reacts with the anhydrous bases. Substances, free of hydroxylic groups, but the showing properties of the bases, napr, ammonia and many organic compounds are known (amines, etc.). In water solutions to - t there are no free hydrogen ions of H+, and there are hydroxonium ions (gidroniya) H3O+ formed as a result of interaction to - t with water molecules, e.g. HCl + H 2 O —> H 3 O + + Cl - .

The protolytic (proton) theory of acids and the bases offered by the Danish fizikokhimik J. N. Bronsted is deprived of many shortcomings inherent in Arrhenius's theory.

According to J. N. Bronsted, to - that is this substance capable to give protons (the donor of protons), and the basis — the substance capable to attach protons (an acceptor of protons). A ratio between To. and the lake is defined by the general scheme: acid = basis + proton. Everyone to - that has the basis interfaced to it formed by eliminating from given to - you a proton, and each basis has interfaced to it to - that, formed as a result of accession of a proton to it.

According to Bronsted's theory, acid-base interaction can be expressed by the following general equation:

also consists in transition of a proton from to - you are HA to the basis of B and education new to - you are BH+ and the new basis And-. Indexes I and II in this equation noted couples interfaced To. and lake. Reaction of acid-base interaction comes to an end with establishment of a so-called protolytic equilibrium between two couples interfaced To. and lake. Below examples of such balances are given:

CH 3 COOH + H 2 <O -> CH 3 COO - + H 3 O +

H 2 O + NH 3 <-> OH - + NH 4 +

HSO 4 - + OH - <-> SO 4 2- + H 2 O.

Follows from the given examples that in a role To. and islands can act not only electroneutral molecules, but also and ions.

The same substance can prove as to - that or as the basis depending on with what other substance it interacts. Binding energy of substance with a proton has crucial importance. So, in a number of the substances NH 3 — H 2 O — HCl this energy is maximum for NH 3 also it is minimum for HCl. Therefore water reacts with ammonia as to - that, and with hydrogen chloride as the basis:

H 2 O + NH 3 = NH 4 + + OH -  ;

HCl + H 2 O = H 3 O + + Cl - .

Thus, «acid» and «basis» of a concept dynamic since acid-base properties of substances are shown only at their interaction.

Sil K. and the lake, according to Bronsted's theory, for any solvents is defined by the size of a constant of the corresponding protolytic equilibrium. So, relative force to - you ON on to - those BH+ is equal:

Kp = [BH + ] * [A - ] / [HA] * [B]

where square brackets designated equilibrium concentrations (more precisely than activity) reactants. Sil K. and the lake in water solutions is determined by sizes of the constants Ka and Kb, as well as by Arrhenius's theory.

The protolytic theory To. and considerably broadened the lake and deepened representations about To. and lake. However do not hold in a framework of this theory aprotic to - you, i.e. the substances having properties to - t, but free of hydrogen as a part of the molecules. Properties aprotic to - t are explained by more general theories To. and lake, napr, G. N. Lewis's theory or M. I. Usanovich's theory.

General ways of receiving acids and bases. Effect of water on acid oxides receive to - you (H 2 O + SO 3 -> H 2 SO 4  ; 3H 2 O + P 2 O 5 -> 2H 3 PO 4 etc.), effect of water on the main oxides — the bases (K 2 O + H 2 O —> 2KOH, etc.). K-you receive action on salt flying to - you difficult flying to - that, e.g. 2NaCl + H 2 SO 4 -> HCl + NaHSO 4 . Formed flying to - that separates from reaction mixture distillation. The bases receive similarly: solution of salt of the low solubility basis is affected with solution of well soluble basis, e.g. by MgSO 4 + 2KOH —> Mg(OH) 2 + K 2 SO 4 . The bases of sodium and potassium receive electrolysis of water solutions of their chlorides.

Classification of acids and the bases

K-you classify by basicity (i.e. by number of hydrogen atoms in a molecule to - you, capable to be replaced on metal with salification) and by chemical structure. Salt (HCl) and acetic (CH 3 COOH) to - you can be examples monobasic to - t, sulfuric to - that (H 2 SO 4 ) it is double-base, orthophosphoric to - that (H 3 PO 4 ) trekhosnovna. On chemical structure to - you divide on: a) oxygen and oxygen-free, H concern to the first 2 SO 4 , HNO 3 , H 3 PO 4 etc., to the second — HCl, HBr, HI, H 2 F 2 , H 2 S, HCN, etc.; b) inorganic and organic, organic call those to - you which molecules contain carbon atoms (however coal to - they are H 2 CO 3 and hydrocianic to - they are HCN carry to inorganic), to - you, formed by other elements, call inorganic.

The bases classify by acidity (i.e. by a number of hydroxyl groups in a molecule, capable to be replaced on acid residues with salification) and by water solubility. Can be examples of monoacid bases caustic soda (NaOH), caustic heat (GAME); two-acid — Ba (OH) hydrated baryta 2  ; three-acid — Fe (OH) ferric hydroxide 3 . On water solubility of the basis divide into well soluble (alkalis) and into insoluble; the major alkalis — water solution ammonia (see), caustic heat (see), caustic soda (see). On chemical structure of the basis subdivide as well as to - you, on inorganic and organic. Carry the bases formed by organic compounds to the last. Inorganic bases are formed by inorganic compounds.

To. and lakes classify also by their force, edges is defined by size acid (KA) and main (Kb) of dissociation constants. To strong to - HNO belong there 3 , HCl, H 2 SO 4 with Ka equal 1,0; the size of KA to - t of average force (H 2 F 2 , H 2 SO 3 ) it is equal to 1 — 10 - 4 , and weak to - t (H 2 CO 3 , CH 3 COOH) — 10 - 4 — 10 - 10 .

Nomenclature of acids and bases. Names oxygen-free inorganic to - t include the name of an element which forms it, and the termination - hydrogen (HCl — hydrochloric, H 2 S — hydrosulphuric). In names oxygen to - there is no t of the termination - hydrogen (HNO 3 - nitric to - that, H 2 SO 4 — sulfuric to - that). If the element forms two oxygen to - you, then the name to - you with high content of oxygen terminates on - Nye or - ovy, and the name to - you with the smaller oxygen content — on - isty or - ovisty, e.g. HNO 3 — nitric to - that, HNO 2 — nitrogenous to - that, H 3 AsO 4 — arsenical to - that, H 3 AsO 3 — arsenous to - that. At education by an element more than two oxygen to - t the name to - you with the smallest oxygen content terminate on - ovatisty, and in process of increase in the oxygen content of the termination change on - isty, - aty, - Nye, e.g. HClO — hypochloric, HClO 2 — chloride, HClO 3 — chloric, HClO 4 — chloric to - that.

Names of the bases form, adding to the name of oxide a prefix gidro-, e.g. Ca(OH) 2 — lime hydrate, KOH — potassium hydroxide. According to the international nomenclature of the basis call hydroxides, e.g. Fe(OH) 2 — ferrous hydroxide (II), Fe(OH) 3 — ferrous hydroxide (III), specifying in brackets the valency of metal in this basis.

The provided nomenclature To. and the lake is not strict. Row K. and the lake has historically developed names, connected or with a special method of their receiving, or with their any specific properties. In medical - biol, practice hl are used. obr. empirical names K. and lake, especially organic.

To organic to - there first of all numerous belong carboxylic acids (see). These to - you it is possible to consider as derivatives coal to - you are HO — CO — OH (H 2 CO 3 ), in a cut one hydroxylic group is replaced by the hydrocarbon radical — R or as derivatives of hydrocarbons in which hydrogen atom is replaced on a carboxyl group — COOH. The majority carboxylic to - t have the empirical names indicating an origin or features given to - you. So, HCOOH is called ant to - that since it was for the first time found in the liquid emitted by ants; CH 3 COOH — acetic to - that since it was for the first time found in vinegar, etc. According to the International Geneva nomenclature organic to - you call on those hydrocarbons in which hydrogen atoms are replaced on carboxyl groups. E.g., acetic to - that call metankarbonovy, oil CH 3 (CH) 2 COOH — butankarbonovy etc. (see. Fatty acids ). Substitution in the radical R-carboxylic to - you hydrogen atoms halogens receive galogenkislota, e.g. CH 2 ClCOOH, CHCl 2 COOH, etc. During the replacement in galogenkislota of halogen atoms with hydroxylic groups receive oxyacids (see), NH 2 - groups — amino acids (see). At introduction to a radical R-carboxylic to - you oxygen receive aldehyde - and ketonic acids (see).

Organic to - you can be derivatives not only coal, but also others inorganic polybasic to - t. E.g., from sulfuric to - you produce numerous sulfonic acids (sulfonic to - you) which, unlike carboxylic to - t, are strong acids. From arsenical to - you make arsinic to - you which example can be cacodylic to - that (CH 3 ) 2 AsOOH, salt a cut find application in medicine.

Quantitative definition of many To. and lakes make titrimetric (see. Neutralizations method ).

Action on a human body

To. and lakes render on a human body to a thicket local, but to some extent and resorptive action.

Acids

Acids cause irritation, chemical. burn (see), inflammation (see), up to a coagulative necrosis and perforation, coagulation of proteins and irritation of sensory nerves, destruction of fabrics. Owing to coagulation of proteins the scab, color and the sizes is formed to-rogo depend by nature, concentration and quantities to - you, and as a result of destruction of blood vessels and erythrocytes and change of hemoglobin a scab can get the corresponding additional coloring.

Acids at introduction through a mouth first of all affect a digestive tract: the oral cavity, a gullet and a stomach, is more rare upper parts of intestines. In addition to the severe pains which are followed by attacks of fear develops shock (see), collapse (see). Pupils are expanded and are not mobile, pulse threadlike, an asthma, a hoarseness, cough, vomiting the blood-red masses or blood, a bloody chair, an anury. Spasms can develop, the coma, asphyxia, the Chemical burn owing to diffusion to - you can cause changes in bodies, adjacent to a stomach and intestines, and in large vessels.

During the swallowing concentrated nitric, salt and others flying to - t penetration of their vapors into a windpipe very quickly causes a heavy asthma, hypostasis of phonatory bands (see. Throat ), what can bring to asphyxia (see).

At absorption to - the t can be shown their resorptive action. The more deeply gets to - that into intestines, the poisoning proceeds heavier. Hydrocianic, oxalic, salicylic to - you render hl. obr. the systemic poisoning effect on an organism, first of all on c. N of page and blood.

The bases

Manifestation of toxic action of the bases depends on their concentration and the nature of a cation. They have the cauterizing effect, cause dissolution of proteins with formation of albuminates, easily injure epidermis, are capable to take away water, to saponify fats and to cause a chemical burn. The picture of a burn is characterized by education whitish-gray, sometimes a brownish soft scab, and in the subsequent — a kolikvatsionny necrosis. The bases cause extensive destructions of fabrics owing to penetration deep into. The chemical burn is complicated by a reactive inflammation. The bases cause formation of more rough hems, than to - you. Most strongly the bases injure mucous membranes. Often mucous membranes of an oral cavity, a gullet, a stomach, intestines, eyes are surprised.

Symptoms of poisoning: severe pains, vomiting, in a stage of jellylike swelling and a kolikvation — destruction of blood vessels, rejection of the mucous membrane impregnated with blood, perforation. The chemical burn can cause shock, a collapse and sudden death.

Acids and the bases in the medicolegal relation

Court. - have medical value both inorganic, and organic to - you and the bases. Most often poisonings are caused acetic, sulfuric, nitric, salt and others to-tami. From the bases of poisoning most often are caused by caustic alkalis — caustic heat, caustic soda, ammonium hydroxide, sodium silicate (silicate glue). Poisonings To. and lakes are, as a rule, household, separate production intoxications are less often noted.

At a research of the dead as a result of poisoning to - that notes the changes characteristic of effect of pyretics: a chemical burn of skin in corners of a mouth, mucous membranes, oral cavities, a gullet, a stomach. The mucous membrane of a stomach often turns into the scab which is easily removed from an underlying layer. Contents of this scab differ markedly acid reaction, a tar-like consistence and in dark brown color. The wall of a stomach can have thinning and perforation. The mucous membrane of a gullet and a stomach at poisoning nitric to - that has an appearance of tannage, easily separates, is painted in yellow color, and naked submucosal — in pinkish-red or grayish-red color. Blood vessels of an abdominal cavity are filled with dense red-black clots. Histologically the full necrosis of walls of a gullet, stomach and often a duodenum comes to light (fusion of walls, hypostasis of a submucosal layer can be noted). In gleams of vessels of bodies of a digestive tract and a mesentery the crumbling henna-red conglomerates of the turned blood are found, but the structure of uniform elements in them can be tracked. Profound dystrophic changes of a mucous membrane of a duodenum, dystrophic changes and loss of bilious pigments in a liver are noted.

At court. - the chemical proof of poisoning to - that acetic and hydrocianic to - you are removed from internals by wet distillation and are found in distillate by means of the corresponding qualitative tests. Quantitative definition is made by method of neutralization (in a case with acetic to - that) and argentometric (at poisonings hydrocianic to - that). Sulfuric, nitric and salt to - you are isolated by dialysis (cm). Their quantitative definition is made by titration of dialyzate solution of caustic alkali.

At a research of the dead as a result of poisoning with any basis chemical burns of a chin, lips, oral cavities, a gullet, a stomach are observed. The mucous membrane of a stomach soft, bulked up, transparent, but can be painted in black color owing to plentiful hemorrhage in submucosal. The burn of a mucous membrane of a small intestine and hemorrhage on its surface is noted.

Gistol, a picture is characterized by a necrosis of a mucous membrane of a gullet and stomach with a kolikvation, an ulceration of a surface, swelling or fatty dystrophy of a liver, the centers of a necrosis which are located in the centers of hepatic segments with a diskompleksation of cells can be observed. In lungs focal hemorrhages, emergence of small sites of pneumonia with leukocytic exudate are noted. In a stomach, a gullet, a liver the phenomena of a reactive inflammation, an autolysis, rejection of nekrotizirovanny sites and regeneration can be found.

The bases from internals isolate dialysis. Detection is based on qualitative tests on hydroxylic ions by various indicators in the presence of excess of barium chloride and on existence of the corresponding cation. Quantitative definition is made by titration of dialyzate solution to - you.

About first aid at poisonings To. both the lake and measures of their prevention, and also about occupational health in production To. and the lake — see article Poisonings and articles according to names separate To. and lake (e.g., Nitric acid , Caustic heat , Caustic soda , Hydrochloric acid etc.).


Table. The most important properties of acids and bases




Bibliography: Bell R. D. A proton in chemistry, the lane with English, M., 1977; Gulyanits-ky And. Reactions of acids and the bases in analytical chemistry, the lane with polsk., M., 1975, bibliogr.; Tay M. K. iselbin. Theoretical inorganic chemistry, the lane with English, M., 1976; Shatenstein A. I. Theories of acids and bases, L., 1949; Shvaykova M. D. Toxicological chemistry, M., 1975.


B. P. Mishin; A. F. Rubtsov (court. medical).

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