What type of chemical is acid? Inorganic acids

Classification of inorganic substances with examples of compounds

Now let's analyze the classification scheme presented above in more detail.

As we see, first of all, all inorganic substances are divided into simple And complex:

Simple substances These are substances that are formed by atoms of only one chemical element. For example, simple substances are hydrogen H2, oxygen O2, iron Fe, carbon C, etc.

Among simple substances there are metals, nonmetals And noble gases:

Metals formed by chemical elements located below the boron-astatine diagonal, as well as all elements located in side groups.

Noble gases formed by chemical elements of group VIIIA.

Nonmetals are formed respectively by chemical elements located above the boron-astatine diagonal, with the exception of all elements of side 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 from. However, for many chemical elements the phenomenon of allotropy is widespread. Allotropy is the phenomenon when one chemical element is capable of forming 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 are substances formed by atoms of two or more chemical elements.

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, there are 5 main classes, namely oxides, bases, amphoteric hydroxides, acids and salts:

Oxides - complex substances formed by two chemical elements, one of which is oxygen in the oxidation state -2.

The general formula of 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 (III) oxide; CuO—copper(II) oxide; N 2 O 5 - nitric oxide (V)

You can often find information that the valency of an element is indicated in parentheses, but this is not the case. So, for example, the oxidation state of nitrogen N 2 O 5 is +5, and the valence, 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 - zinc oxide.

Oxides classification

Oxides, according to their ability to form salts when interacting with acids or bases, are divided accordingly into salt-forming And non-salt-forming.

There are few non-salt-forming oxides; they are all formed by nonmetals 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 basic, acidic And amphoteric.

Basic oxides These are oxides that, when reacting with acids (or acid oxides), form salts. Basic oxides include metal oxides in the oxidation state +1 and +2, with the exception of the oxides BeO, ZnO, SnO, PbO.

Acidic oxides These are oxides that, when reacting with bases (or basic oxides), form salts. Acidic 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 are called oxides that 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 the oxidation states +3, +4, as well as the oxides BeO, ZnO, SnO, and PbO as exceptions.

Some metals can form all three types of salt-forming oxides. For example, chromium forms the basic oxide CrO, the amphoteric oxide Cr 2 O 3 and the acidic oxide CrO 3.

As you can see, 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.

Reasons

Reasons - compounds with the formula Me(OH) x, where x most often equal to 1 or 2.

Classification of bases

Bases are classified according to the number of hydroxyl groups in one structural unit.

Bases with one hydroxo group, i.e. type MeOH is called monoacid bases, with two hydroxo groups, i.e. type Me(OH) 2, respectively, diacid etc.

Bases are also divided into soluble (alkalis) and insoluble.

Alkalies include exclusively hydroxides of alkali and alkaline earth metals, as well as thallium hydroxide TlOH.

Nomenclature of bases

The name of the foundation is based on 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 whose molecules 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 the acidic residue.

For example, acids include compounds such as H2SO4, HCl, HNO3, HNO2, etc.

Classification of acids

According to the number of hydrogen atoms that can be replaced by a metal, acids are divided into:

- O base acids: HF, HCl, HBr, HI, HNO 3 ;

- d basic acids: H 2 SO 4, H 2 SO 3, H 2 CO 3;

- T rehobasic 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 tetra- but monobasic. The basicity of organic acids is determined by the number of carboxyl groups (-COOH) in the molecule.

Also, based on the presence of oxygen in the molecules, acids are divided into oxygen-free (HF, HCl, HBr, etc.) and oxygen-containing (H 2 SO 4, HNO 3, H 3 PO 4, etc.). Oxygen-containing acids are also called oxoacids.

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 is a must-learn.

In some cases, a number of the following rules can make memorization easier.

As can be seen from the table above, the construction of systematic names of oxygen-free acids is as follows:

For example:

HF—hydrofluoric acid;

HCl—hydrochloric acid;

H 2 S is hydrosulfide acid.

The names of acidic residues of oxygen-free acids are based on 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 acid hydroxides because they contain hydroxyl groups (OH). For example, this can be seen from the following graphical formulas of some oxygen-containing acids:

Thus, sulfuric acid can otherwise be called sulfur (VI) hydroxide, nitric acid - nitrogen (V) hydroxide, phosphoric acid - phosphorus (V) hydroxide, etc. In this case, the number in brackets characterizes the degree of oxidation of the acid-forming element. This version 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 tasks on the classification of inorganic substances.

Amphoteric hydroxides

Amphoteric hydroxides - metal hydroxides exhibiting a dual nature, i.e. capable of exhibiting both the properties of acids and the properties of bases.

Metal hydroxides in oxidation states +3 and +4 are amphoteric (as are oxides).

Also, as exceptions, amphoteric hydroxides include the compounds Be(OH) 2, Zn(OH) 2, Sn(OH) 2 and Pb(OH) 2, despite the oxidation state 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 Al(OH)3 or the meta form 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:

Salts

For example, salts include compounds such as KCl, Ca(NO 3) 2, NaHCO 3, etc.

The definition presented above 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 - (methyl ammonium chloride), etc.

Classification of salts

On the other hand, salts can be considered as products of the replacement of hydrogen cations H + in an acid with other cations, or as products of the replacement of hydroxide ions in bases (or amphoteric hydroxides) with other anions.

With complete replacement, the so-called average or normal salt. For example, with complete replacement of hydrogen cations in sulfuric acid with sodium cations, an average (normal) salt Na 2 SO 4 is formed, and with complete replacement of hydroxide ions in the base Ca (OH) 2 with acidic residues of nitrate ions, an average (normal) salt is formed Ca(NO3)2.

Salts obtained by incomplete replacement of hydrogen cations in a dibasic (or more) acid with metal cations are called acidic. Thus, when hydrogen cations in sulfuric acid are incompletely replaced by sodium cations, the acid salt NaHSO 4 is formed.

Salts that are formed by incomplete replacement of hydroxide ions in two-acid (or more) bases are called bases. O strong salts. For example, with incomplete replacement of hydroxide ions in the base Ca(OH) 2 with nitrate ions, a base is formed O clear salt Ca(OH)NO3.

Salts consisting of cations of two different metals and anions of acidic residues of only one acid are called double salts. So, for example, double salts are KNaCO 3, KMgCl 3, etc.

If a salt is formed by one type of cations 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 the replacement of hydrogen cations in acids with metal cations or products of the replacement of hydroxide ions in bases with anions of acidic residues. These are complex salts. For example, complex salts are sodium tetrahydroxozincate and tetrahydroxoaluminate with the formulas Na 2 and Na, respectively. Complex salts can most often be recognized among others by the presence of square brackets in the formula. However, you need to understand that in order for a substance to be classified as a salt, it must contain some cations other than (or instead of) H +, and the anions must contain some anions other than (or instead of) OH -. For example, the compound H2 does not belong to the class of complex salts, since when it dissociates from cations, only hydrogen cations H+ are present in the solution. Based on the type of dissociation, this substance should rather be classified as an oxygen-free complex acid. Likewise, the OH compound does not belong to salts, because this compound consists of cations + and hydroxide ions OH -, i.e. it should be considered a comprehensive foundation.

Nomenclature of salts

Nomenclature of medium and acid salts

The name of medium and acid salts is based on the principle:

If the oxidation state of a metal in complex substances is constant, then it is not indicated.

The names of acid residues were given above when considering the nomenclature of acids.

For example,

Na 2 SO 4 - sodium sulfate;

NaHSO 4 - sodium hydrogen sulfate;

CaCO 3 - calcium carbonate;

Ca(HCO 3) 2 - calcium bicarbonate, etc.

Nomenclature of basic salts

The names of the main salts are based on the principle:

For example:

(CuOH) 2 CO 3 - copper (II) hydroxycarbonate;

Fe(OH) 2 NO 3 - iron (III) dihydroxonitrate.

Nomenclature of complex salts

The nomenclature of complex compounds is much more complicated, and to pass the Unified State Exam you do not need to know much about the nomenclature of complex salts.

You should be able to name complex salts obtained by reacting alkali solutions with amphoteric hydroxides. For example:

*The same colors in the formula and name indicate the corresponding elements of the formula and name.

Trivial names of inorganic substances

By trivial names we mean the names of substances that are not related, or weakly related, to their composition and structure. Trivial names are determined, as a rule, either by historical reasons or by the physical or chemical properties of these compounds.

List of trivial names of inorganic substances that you need to know:

Acids are complex substances whose molecules include hydrogen atoms that can be replaced or exchanged for metal atoms and an acid residue.

Based on 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 oxygen-free(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 the 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 its molecule contains one hydrogen atom, 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.

Acidic residues may consist of one atom (-Cl, -Br, -I) - these are simple acidic residues, or they may consist of a group of atoms (-SO 3, -PO 4, -SiO 3) - these are complex residues.

In aqueous solutions, during exchange and substitution reactions, acidic residues are not destroyed:

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 names of acids will be when the element exhibits a higher valence (the acid molecule contains a high content of oxygen atoms). If the element exhibits a lower valence, the ending in the name of the acid will be “empty”: HNO 3 - nitric, HNO 2 - nitrogenous.

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 oxygen-free acids. Oxygen-free acids are also obtained by direct synthesis from hydrogen and a non-metal, followed by dissolving 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 are acids.

Under normal conditions, acids exist in both liquid and solid states.

Chemical properties of acids

Acid solutions act on indicators. All acids (except silicic) are highly soluble in water. Special substances - indicators allow you to determine the presence of acid.

Indicators are substances of complex structure. They change color depending on their interaction with different chemicals. In neutral solutions they have one color, in solutions of bases they have another color. When interacting with an acid, they change their color: the methyl orange indicator turns red, and 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 base 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 acids to interact with metals, certain conditions must be met:

1. the metal must be sufficiently active in relation 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 hydrogen ions H +).

When chemical reactions of acid with metals occur, 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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Acids are complex substances whose molecules include hydrogen atoms that can be replaced or exchanged for metal atoms and an acid residue.

Based on 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 oxygen-free(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 the 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 its molecule contains one hydrogen atom, 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.

Acidic residues may consist of one atom (-Cl, -Br, -I) - these are simple acidic residues, or they may consist of a group of atoms (-SO 3, -PO 4, -SiO 3) - these are complex residues.

In aqueous solutions, during exchange and substitution reactions, acidic residues are not destroyed:

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 names of acids will be when the element exhibits a higher valence (the acid molecule contains a high content of oxygen atoms). If the element exhibits a lower valence, the ending in the name of the acid will be “empty”: HNO 3 - nitric, HNO 2 - nitrogenous.

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 oxygen-free acids. Oxygen-free acids are also obtained by direct synthesis from hydrogen and a non-metal, followed by dissolving 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 are acids.

Under normal conditions, acids exist in both liquid and solid states.

Chemical properties of acids

Acid solutions act on indicators. All acids (except silicic) are highly soluble in water. Special substances - indicators allow you to determine the presence of acid.

Indicators are substances of complex structure. They change color depending on their interaction with different chemicals. In neutral solutions they have one color, in solutions of bases they have another color. When interacting with an acid, they change their color: the methyl orange indicator turns red, and 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 base 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 acids to interact with metals, certain conditions must be met:

1. the metal must be sufficiently active in relation 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 hydrogen ions H +).

When chemical reactions of acid with metals occur, 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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Let's look at the most common acid formulas found in textbooks:

It is easy to notice that all acid formulas have in common the presence of hydrogen atoms (H), which comes first in the formula.

Determination of the valence of an acid residue

From the above list it can be seen that the number of these atoms may differ. Acids that contain only one hydrogen atom are called monobasic (nitric, hydrochloric, and others). Sulfuric, carbonic, and silicic acids are dibasic, since their formulas contain two H atoms. A tribasic phosphoric acid molecule contains three hydrogen atoms.

Thus, the amount of H in the formula characterizes the basicity of the acid.

The atom or group of atoms that are written after hydrogen are called acid residues. For example, in hydrosulfide acid the residue consists of one atom - S, and in phosphoric, sulfurous and many others - of two, and one of them is necessarily oxygen (O). On this basis, all acids are divided into oxygen-containing and oxygen-free.

Each acid residue has a certain valence. It is equal to the number of H atoms in the molecule of this acid. The valence of the HCl residue is equal to one, since it is a monobasic acid. Residues of nitric, perchloric, and nitrous acids have the same valency. The valency of the sulfuric acid residue (SO 4) is two, since there are two hydrogen atoms in its formula. Trivalent phosphoric acid residue.

Acidic residues - anions

In addition to valence, acid residues have charges and are anions. Their charges are indicated in the solubility table: CO 3 2−, S 2−, Cl− and so on. Please note: the charge of the acidic residue is numerically the same as its valency. For example, in silicic acid, the formula of which is H 2 SiO 3, the acid residue SiO 3 has a valence of II and a charge of 2-. Thus, knowing the charge of the acidic residue, it is easy to determine its valence and vice versa.

Summarize. Acids are compounds formed by hydrogen atoms and acidic residues. From the point of view of the theory of electrolytic dissociation, another definition can be given: acids are electrolytes, in solutions and melts of which hydrogen cations and anions of acid residues are present.

Hints

Chemical formulas of acids are usually learned by heart, as are their names. If you have forgotten how many hydrogen atoms are in a particular formula, but you know what its acidic residue looks like, the solubility table will come to your aid. The charge of the residue coincides in modulus with the valence, and that with the amount of H. For example, you remember that the remainder of carbonic acid is CO 3 . Using the solubility table, you determine that its charge is 2-, which means it is divalent, that is, carbonic acid has the formula H 2 CO 3.

There is often confusion with the formulas of sulfuric and sulfurous, as well as nitric and nitrous acids. Here, too, there is one point that makes it easier to remember: the name of the acid from the pair in which there are more oxygen atoms ends in -naya (sulfuric, nitric). An acid with fewer oxygen atoms in the formula has a name ending in -istaya (sulphurous, nitrogenous).

However, these tips will only help if the acid formulas are familiar to you. Let's repeat them again.