Acids are complex substances whose molecules consist of hydrogen atoms (capable of being replaced by metal atoms) associated with an acid residue.
general characteristics
Acids are classified into oxygen-free and oxygen-containing, as well as organic and inorganic.
Rice. 1. Classification of acids - anoxic and oxygen-containing.
Anoxic acids are solutions in water of such binary compounds as hydrogen halides or hydrogen sulfide. In solution, the polar covalent bond between hydrogen and an electronegative element is polarized by the action of dipole water molecules, and the molecules break up into ions. the presence of hydrogen ions in the substance and allows you to call aqueous solutions of these binary compounds acids.
Acids are named after the name of the binary compound by adding the ending -naya. for example, HF is hydrofluoric acid. The acid anion is called by the name of the element by adding the ending -id, for example, Cl - chloride.
Oxygen-containing acids (oxoacids)- these are acid hydroxides dissociating according to the acid type, that is, as protoliths. Their general formula is E (OH) mOn, where E is a non-metal or a metal with variable valence in the highest oxidation state. provided that n is 0, then the acid is weak (H 2 BO 3 - boric), if n \u003d 1, then the acid is either weak or of medium strength (H 3 PO 4 - orthophosphoric), if n is greater than or equal to 2, then acid is considered strong (H 2 SO 4).
Rice. 2. Sulfuric acid.
Acid hydroxides correspond to acid oxides or acid anhydrides, for example, sulfuric acid corresponds to sulfuric anhydride SO 3 .
Chemical properties of acids
Acids have a number of properties that distinguish them from salts and other chemical elements:
- Action on indicators. How acid protolytes dissociate to form H+ ions, which change the color of the indicators: a purple litmus solution turns red, and an orange methyl orange solution turns pink. Polybasic acids dissociate in steps, and each subsequent stage is more difficult than the previous one, since increasingly weaker electrolytes dissociate in the second and third steps:
H 2 SO 4 \u003d H + + HSO 4 -
The color of the indicator depends on whether the acid is concentrated or diluted. So, for example, when litmus is lowered into concentrated sulfuric acid, the indicator turns red, but in dilute sulfuric acid, the color does not change.
- Neutralization reaction, that is, the interaction of acids with bases, resulting in the formation of salt and water, always occurs if at least one of the reagents is strong (base or acid). The reaction does not go if the acid is weak, the base is insoluble. For example, there is no reaction:
H 2 SiO 3 (weak, water-insoluble acid) + Cu (OH) 2 - no reaction
But in other cases, the neutralization reaction with these reagents goes:
H 2 SiO 3 + 2KOH (alkali) \u003d K 2 SiO 3 + 2H 2 O
- Interaction with basic and amphoteric oxides:
Fe 2 O 3 + 3H 2 SO 4 \u003d Fe 2 (SO 4) 3 + 3H 2 O
- The interaction of acids with metals, standing in a series of voltages to the left of hydrogen, leads to a process in which salt is formed and hydrogen is released. This reaction is easy if the acid is strong enough.
Nitric acid and concentrated sulfuric acid react with metals by reducing not hydrogen, but the central atom:
Mg + H 2 SO 4 + MgSO 4 + H 2
- The interaction of acids with salts occurs if the result is a weak acid. If the salt that reacts with the acid is soluble in water, then the reaction will also proceed if an insoluble salt is formed:
Na 2 SiO 3 (soluble salt of a weak acid) + 2HCl (strong acid) \u003d H 2 SiO 3 (weak insoluble acid) + 2NaCl (soluble salt)
Many acids are used in industry, for example, acetic acid is necessary for the preservation of meat and fish products.
acids complex substances are called, the composition of the molecules of which includes hydrogen atoms that can be replaced or exchanged for metal atoms and an acid residue.
According to the presence or absence of oxygen in the molecule, acids are divided into oxygen-containing(H 2 SO 4 sulfuric acid, H 2 SO 3 sulfurous acid, HNO 3 nitric acid, H 3 PO 4 phosphoric acid, H 2 CO 3 carbonic acid, H 2 SiO 3 silicic acid) and anoxic(HF hydrofluoric acid, HCl hydrochloric acid (hydrochloric acid), HBr hydrobromic acid, HI hydroiodic acid, H 2 S hydrosulfide acid).
Depending on the number of hydrogen atoms in an acid molecule, acids are monobasic (with 1 H atom), dibasic (with 2 H atoms) and tribasic (with 3 H atoms). For example, nitric acid HNO 3 is monobasic, since there is one hydrogen atom in its molecule, sulfuric acid H 2 SO 4 – dibasic, etc.
There are very few inorganic compounds containing four hydrogen atoms that can be replaced by a metal.
The part of an acid molecule without hydrogen is called an acid residue.
Acid Residue they can consist of one atom (-Cl, -Br, -I) - these are simple acid residues, or they can - from a group of atoms (-SO 3, -PO 4, -SiO 3) - these are complex residues.
In aqueous solutions, acid residues are not destroyed during exchange and substitution reactions:
H 2 SO 4 + CuCl 2 → CuSO 4 + 2 HCl
The word anhydride means anhydrous, that is, an acid without water. For example,
H 2 SO 4 - H 2 O → SO 3. Anoxic acids do not have anhydrides.
Acids get their name from the name of the acid-forming element (acid-forming agent) with the addition of the endings “naya” and less often “vaya”: H 2 SO 4 - sulfuric; H 2 SO 3 - coal; H 2 SiO 3 - silicon, etc.
The element can form several oxygen acids. In this case, the indicated endings in the name of the acids will be when the element exhibits the highest valence (the acid molecule has a large content of oxygen atoms). If the element exhibits a lower valence, the ending in the name of the acid will be “pure”: HNO 3 - nitric, HNO 2 - nitrous.
Acids can be obtained by dissolving anhydrides in water. If the anhydrides are insoluble in water, the acid can be obtained by the action of another stronger acid on the salt of the required acid. This method is typical for both oxygen and anoxic acids. Anoxic acids are also obtained by direct synthesis from hydrogen and non-metal, followed by dissolution of the resulting compound in water:
H 2 + Cl 2 → 2 HCl;
H 2 + S → H 2 S.
Solutions of the resulting gaseous substances HCl and H 2 S and are acids.
Under normal conditions, acids are both liquid and solid.
Chemical properties of acids
Acid solutions act on indicators. All acids (except silicic acid) dissolve well in water. Special substances - indicators allow you to determine the presence of acid.
Indicators are substances of complex structure. They change their color depending on the interaction with different chemicals. In neutral solutions, they have one color, in solutions of bases, another. When interacting with acid, they change their color: the methyl orange indicator turns red, the litmus indicator also turns red.
Interact with bases with the formation of water and salt, which contains an unchanged acid residue (neutralization reaction):
H 2 SO 4 + Ca (OH) 2 → CaSO 4 + 2 H 2 O.
Interact with based oxides with the formation of water and salt (neutralization reaction). The salt contains the acid residue of the acid that was used in the neutralization reaction:
H 3 PO 4 + Fe 2 O 3 → 2 FePO 4 + 3 H 2 O.
interact with metals.
For the interaction of acids with metals, certain conditions must be met:
1. the metal must be sufficiently active with respect to acids (in the series of activity of metals, it must be located before hydrogen). The further to the left a metal is in the activity series, the more intensely it interacts with acids;
2. The acid must be strong enough (that is, capable of donating H + hydrogen ions).
During the course of chemical reactions of an acid with metals, a salt is formed and hydrogen is released (except for the interaction of metals with nitric and concentrated sulfuric acids):
Zn + 2HCl → ZnCl 2 + H 2;
Cu + 4HNO 3 → CuNO 3 + 2 NO 2 + 2 H 2 O.
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| Acid formulas | Names of acids | Names of the corresponding salts |
| HClO 4 | chloride | perchlorates |
| HClO 3 | chlorine | chlorates |
| HClO 2 | chloride | chlorites |
| HClO | hypochlorous | hypochlorites |
| H5IO6 | iodine | periodates |
| HIO 3 | iodine | iodates |
| H2SO4 | sulfuric | sulfates |
| H2SO3 | sulphurous | sulfites |
| H2S2O3 | thiosulfuric | thiosulfates |
| H2S4O6 | tetrathionic | tetrathionates |
| HNO3 | nitric | nitrates |
| HNO 2 | nitrogenous | nitrites |
| H3PO4 | orthophosphoric | orthophosphates |
| HPO 3 | metaphosphoric | metaphosphates |
| H3PO3 | phosphorous | phosphites |
| H3PO2 | phosphorous | hypophosphites |
| H2CO3 | coal | carbonates |
| H2SiO3 | silicon | silicates |
| HMnO 4 | manganese | permanganates |
| H2MnO4 | manganese | manganates |
| H2CrO4 | chrome | chromates |
| H2Cr2O7 | dichrome | dichromates |
| HF | hydrofluoric (hydrofluoric) | fluorides |
| HCl | hydrochloric (hydrochloric) | chlorides |
| HBr | hydrobromic | bromides |
| HI | hydroiodic | iodides |
| H 2 S | hydrogen sulfide | sulfides |
| HCN | hydrocyanic | cyanides |
| HOCN | cyanic | cyanates |
Let me briefly remind you with specific examples of how salts should be properly named.
Example 1. Salt K 2 SO 4 is formed by the rest of sulfuric acid (SO 4) and metal K. Salts of sulfuric acid are called sulfates. K 2 SO 4 - potassium sulfate.
Example 2. FeCl 3 - the composition of the salt includes iron and the rest of hydrochloric acid (Cl). Name of the salt: iron(III) chloride. Please note: in this case, we not only have to name the metal, but also indicate its valency (III). In the previous example, this was not necessary, since the valency of sodium is constant.
Important: in the name of the salt, the valency of the metal should be indicated only if this metal has a variable valency!
Example 3. Ba (ClO) 2 - the composition of the salt includes barium and the remainder of hypochlorous acid (ClO). Name of salt: barium hypochlorite. The valency of the Ba metal in all its compounds is two, it is not necessary to indicate it.
Example 4. (NH 4) 2 Cr 2 O 7. The NH 4 group is called ammonium, the valence of this group is constant. Salt name: ammonium dichromate (bichromate).
In the above examples, we met only the so-called. medium or normal salts. Acid, basic, double and complex salts, salts of organic acids will not be discussed here.
If you are interested not only in the nomenclature of salts, but also in the methods for their preparation and chemical properties, I recommend that you refer to the relevant sections of the reference book on chemistry: "
Classification of inorganic substances with examples of compounds
Let us now analyze the classification scheme presented above in more detail.
As we can see, first of all, all inorganic substances are divided into simple and complex:
simple substances substances that are formed by atoms of only one chemical element are called. For example, simple substances are hydrogen H 2 , oxygen O 2 , iron Fe, carbon C, etc.
Among simple substances, there are metals, nonmetals and noble gases:
Metals are formed by chemical elements located below the boron-astat diagonal, as well as by all elements that are in side groups.
noble gases formed by chemical elements of group VIIIA.
non-metals formed respectively by chemical elements located above the boron-astat diagonal, with the exception of all elements of secondary subgroups and noble gases located in group VIIIA:
The names of simple substances most often coincide with the names of the chemical elements whose atoms they are formed. However, for many chemical elements, the phenomenon of allotropy is widespread. Allotropy is the phenomenon when one chemical element is able to form several simple substances. For example, in the case of the chemical element oxygen, the existence of molecular compounds with the formulas O 2 and O 3 is possible. The first substance is usually called oxygen in the same way as the chemical element whose atoms it is formed, and the second substance (O 3) is usually called ozone. The simple substance carbon can mean any of its allotropic modifications, for example, diamond, graphite or fullerenes. The simple substance phosphorus can be understood as its allotropic modifications, such as white phosphorus, red phosphorus, black phosphorus.
Complex Substances
complex substances Substances made up of atoms of two or more elements are called.
So, for example, complex substances are ammonia NH 3, sulfuric acid H 2 SO 4, slaked lime Ca (OH) 2 and countless others.
Among complex inorganic substances, 5 main classes are distinguished, namely oxides, bases, amphoteric hydroxides, acids and salts:
oxides - complex substances formed by two chemical elements, one of which is oxygen in the -2 oxidation state.
The general formula for oxides can be written as E x O y, where E is the symbol of a chemical element.
Nomenclature of oxides
The name of the oxide of a chemical element is based on the principle:
For example:
Fe 2 O 3 - iron oxide (III); CuO, copper(II) oxide; N 2 O 5 - nitric oxide (V)
Often you can find information that the valency of the element is indicated in brackets, but this is not the case. So, for example, the oxidation state of nitrogen N 2 O 5 is +5, and the valency, oddly enough, is four.
If a chemical element has a single positive oxidation state in compounds, then the oxidation state is not indicated. For example:
Na 2 O - sodium oxide; H 2 O - hydrogen oxide; ZnO is zinc oxide.
Classification of oxides
Oxides, according to their ability to form salts when interacting with acids or bases, are divided, respectively, into salt-forming and non-salt-forming.
There are few non-salt-forming oxides, all of them are formed by non-metals in the oxidation state +1 and +2. The list of non-salt-forming oxides should be remembered: CO, SiO, N 2 O, NO.
Salt-forming oxides, in turn, are divided into main, acidic and amphoteric.
Basic oxides called such oxides, which, when interacting with acids (or acid oxides), form salts. The main oxides include metal oxides in the oxidation state +1 and +2, with the exception of oxides of BeO, ZnO, SnO, PbO.
Acid oxides called such oxides, which, when interacting with bases (or basic oxides), form salts. Acid oxides are almost all oxides of non-metals with the exception of non-salt-forming CO, NO, N 2 O, SiO, as well as all metal oxides in high oxidation states (+5, +6 and +7).
amphoteric oxides called oxides, which can react with both acids and bases, and as a result of these reactions form salts. Such oxides exhibit a dual acid-base nature, that is, they can exhibit the properties of both acidic and basic oxides. Amphoteric oxides include metal oxides in oxidation states +3, +4, and, as exceptions, oxides of BeO, ZnO, SnO, PbO.
Some metals can form all three types of salt-forming oxides. For example, chromium forms basic oxide CrO, amphoteric oxide Cr 2 O 3 and acid oxide CrO 3 .
As can be seen, the acid-base properties of metal oxides directly depend on the degree of oxidation of the metal in the oxide: the higher the degree of oxidation, the more pronounced the acidic properties.
Foundations
Foundations - compounds with a formula of the form Me (OH) x, where x most often equal to 1 or 2.
Base classification
Bases are classified according to the number of hydroxo groups in one structural unit.
Bases with one hydroxo group, i.e. type MeOH, called single acid bases with two hydroxo groups, i.e. type Me(OH) 2 , respectively, diacid etc.
Also, the bases are divided into soluble (alkali) and insoluble.
Alkalis include exclusively hydroxides of alkali and alkaline earth metals, as well as thallium hydroxide TlOH.
Base nomenclature
The name of the foundation is built according to the following principle:
For example:
Fe (OH) 2 - iron (II) hydroxide,
Cu (OH) 2 - copper (II) hydroxide.
In cases where the metal in complex substances has a constant oxidation state, it is not required to indicate it. For example:
NaOH - sodium hydroxide,
Ca (OH) 2 - calcium hydroxide, etc.
acids
acids - complex substances, the molecules of which contain hydrogen atoms that can be replaced by a metal.
The general formula of acids can be written as H x A, where H are hydrogen atoms that can be replaced by a metal, and A is an acid residue.
For example, acids include compounds such as H 2 SO 4 , HCl, HNO 3 , HNO 2 , etc.
Acid classification
According to the number of hydrogen atoms that can be replaced by a metal, acids are divided into:
- about monobasic acids: HF, HCl, HBr, HI, HNO 3 ;
- d acetic acids: H 2 SO 4 , H 2 SO 3 , H 2 CO 3 ;
- t rebasic acids: H 3 PO 4 , H 3 BO 3 .
It should be noted that the number of hydrogen atoms in the case of organic acids most often does not reflect their basicity. For example, acetic acid with the formula CH 3 COOH, despite the presence of 4 hydrogen atoms in the molecule, is not four-, but monobasic. The basicity of organic acids is determined by the number of carboxyl groups (-COOH) in the molecule.
Also, according to the presence of oxygen in acid molecules, they are divided into anoxic (HF, HCl, HBr, etc.) and oxygen-containing (H 2 SO 4, HNO 3, H 3 PO 4, etc.). Oxygenated acids are also called oxo acids.
You can read more about the classification of acids.
Nomenclature of acids and acid residues
The following list of names and formulas of acids and acid residues should be learned.
In some cases, a number of the following rules can make memorization easier.
As can be seen from the table above, the construction of the systematic names of anoxic acids is as follows:
For example:
HF, hydrofluoric acid;
HCl, hydrochloric acid;
H 2 S - hydrosulfide acid.
The names of the acid residues of oxygen-free acids are built according to the principle:
For example, Cl - - chloride, Br - - bromide.
The names of oxygen-containing acids are obtained by adding various suffixes and endings to the name of the acid-forming element. For example, if the acid-forming element in an oxygen-containing acid has the highest oxidation state, then the name of such an acid is constructed as follows:
For example, sulfuric acid H 2 S +6 O 4, chromic acid H 2 Cr +6 O 4.
All oxygen-containing acids can also be classified as acidic hydroxides, since hydroxo groups (OH) are found in their molecules. For example, this can be seen from the following graphical formulas of some oxygen-containing acids:
Thus, sulfuric acid may otherwise be called sulfur (VI) hydroxide, nitric acid - nitrogen (V) hydroxide, phosphoric acid - phosphorus (V) hydroxide, etc. The number in brackets characterizes the degree of oxidation of the acid-forming element. Such a variant of the names of oxygen-containing acids may seem extremely unusual to many, but occasionally such names can be found in real KIMs of the Unified State Examination in chemistry in assignments for the classification of inorganic substances.
Amphoteric hydroxides
Amphoteric hydroxides - metal hydroxides exhibiting a dual nature, i.e. able to exhibit both the properties of acids and the properties of bases.
Amphoteric are metal hydroxides in oxidation states +3 and +4 (as well as oxides).
Also, compounds Be (OH) 2, Zn (OH) 2, Sn (OH) 2 and Pb (OH) 2 are included as exceptions to amphoteric hydroxides, despite the degree of oxidation of the metal in them +2.
For amphoteric hydroxides of tri- and tetravalent metals, the existence of ortho- and meta-forms is possible, differing from each other by one water molecule. For example, aluminum (III) hydroxide can exist in the ortho form of Al(OH) 3 or the meta form of AlO(OH) (metahydroxide).
Since, as already mentioned, amphoteric hydroxides exhibit both the properties of acids and the properties of bases, their formula and name can also be written differently: either as a base or as an acid. For example:
salt
So, for example, salts include compounds such as KCl, Ca(NO 3) 2, NaHCO 3, etc.
The above definition describes the composition of most salts, however, there are salts that do not fall under it. For example, instead of metal cations, the salt may contain ammonium cations or its organic derivatives. Those. salts include compounds such as, for example, (NH 4) 2 SO 4 (ammonium sulfate), + Cl - (methylammonium chloride), etc.
Salt classification
On the other hand, salts can be considered as products of substitution of hydrogen cations H + in an acid for other cations, or as products of substitution of hydroxide ions in bases (or amphoteric hydroxides) for other anions.
With complete substitution, the so-called medium or normal salt. For example, with the complete replacement of hydrogen cations in sulfuric acid with sodium cations, an average (normal) salt Na 2 SO 4 is formed, and with the complete replacement of hydroxide ions in the Ca (OH) 2 base with acid residues, nitrate ions form an average (normal) salt Ca(NO3)2.
Salts obtained by incomplete replacement of hydrogen cations in a dibasic (or more) acid with metal cations are called acid salts. So, with incomplete replacement of hydrogen cations in sulfuric acid by sodium cations, an acid salt NaHSO 4 is formed.
Salts that are formed by incomplete substitution of hydroxide ions in two-acid (or more) bases are called basic about salts. For example, with incomplete replacement of hydroxide ions in the Ca (OH) 2 base with nitrate ions, a basic about clear salt Ca(OH)NO 3 .
Salts consisting of cations of two different metals and anions of acid residues of only one acid are called double salts. So, for example, double salts are KNaCO 3 , KMgCl 3 , etc.
If the salt is formed by one type of cation and two types of acid residues, such salts are called mixed. For example, mixed salts are the compounds Ca(OCl)Cl, CuBrCl, etc.
There are salts that do not fall under the definition of salts as products of substitution of hydrogen cations in acids for metal cations or products of substitution of hydroxide ions in bases for anions of acid residues. These are complex salts. So, for example, complex salts are sodium tetrahydroxozincate and tetrahydroxoaluminate with the formulas Na 2 and Na, respectively. Recognize complex salts, among others, most often by the presence of square brackets in the formula. However, it must be understood that in order for a substance to be classified as a salt, its composition must include any cations, except for (or instead of) H +, and from the anions there must be any anions in addition to (or instead of) OH -. For example, the compound H 2 does not belong to the class of complex salts, since only hydrogen cations H + are present in solution during its dissociation from cations. According to the type of dissociation, this substance should rather be classified as an oxygen-free complex acid. Similarly, the OH compound does not belong to the salts, because this compound consists of cations + and hydroxide ions OH -, i.e. it should be considered a complex basis.
Salt nomenclature
Nomenclature of medium and acid salts
The name of medium and acid salts is based on the principle:
If the degree of oxidation of the metal in complex substances is constant, then it is not indicated.
The names of the acid residues were given above when considering the nomenclature of acids.
For example,
Na 2 SO 4 - sodium sulfate;
NaHSO 4 - sodium hydrosulfate;
CaCO 3 - calcium carbonate;
Ca (HCO 3) 2 - calcium bicarbonate, etc.
Nomenclature of basic salts
The names of the main salts are built according to the principle:
For example:
(CuOH) 2 CO 3 - copper (II) hydroxocarbonate;
Fe (OH) 2 NO 3 - iron (III) dihydroxonitrate.
Nomenclature of complex salts
The nomenclature of complex compounds is much more complicated, and you don’t need to know much from the nomenclature of complex salts to pass the exam.
One should be able to name complex salts obtained by the interaction of alkali solutions with amphoteric hydroxides. For example:
*The same colors in the formula and the name indicate the corresponding elements of the formula and the name.
Trivial names of inorganic substances
Trivial names are understood as the names of substances that are not related, or weakly related to their composition and structure. Trivial names are due, as a rule, either to historical reasons or to the physical or chemical properties of these compounds.
List of trivial names of inorganic substances that you need to know:
| Na 3 | cryolite |
| SiO2 | quartz, silica |
| FeS 2 | pyrite, iron pyrite |
| CaSO 4 ∙2H 2 O | gypsum |
| CaC2 | calcium carbide |
| Al 4 C 3 | aluminum carbide |
| KOH | caustic potash |
| NaOH | caustic soda, caustic soda |
| H2O2 | hydrogen peroxide |
| CuSO 4 ∙5H 2 O | blue vitriol |
| NH4Cl | ammonia |
| CaCO3 | chalk, marble, limestone |
| N2O | laughing gas |
| NO 2 | brown gas |
| NaHCO3 | food (drinking) soda |
| Fe 3 O 4 | iron oxide |
| NH 3 ∙H 2 O (NH 4 OH) | ammonia |
| CO | carbon monoxide |
| CO2 | carbon dioxide |
| SiC | carborundum (silicon carbide) |
| PH 3 | phosphine |
| NH3 | ammonia |
| KClO 3 | berthollet salt (potassium chlorate) |
| (CuOH) 2 CO 3 | malachite |
| CaO | quicklime |
| Ca(OH)2 | slaked lime |
| transparent aqueous solution of Ca(OH) 2 | lime water |
| a suspension of solid Ca (OH) 2 in its aqueous solution | milk of lime |
| K2CO3 | potash |
| Na2CO3 | soda ash |
| Na 2 CO 3 ∙10H 2 O | crystal soda |
| MgO | magnesia |
