Composition classification characteristic properties of acids. inorganic acids

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:

- O 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 O salts. For example, with incomplete replacement of hydroxide ions in the Ca (OH) 2 base with nitrate ions, a basic O 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:

Do not underestimate the role of acids in our lives, because many of them are simply irreplaceable in everyday life. First, let's remember what acids are. These are complex substances. The formula is written as follows: HnA, where H is hydrogen, n is the number of atoms, A is the acid residue.

The main properties of acids include the ability to replace the molecules of hydrogen atoms with metal atoms. Most of them are not only caustic, but also very poisonous. But there are also those that we encounter constantly, without harm to our health: vitamin C, citric acid, lactic acid. Consider the basic properties of acids.

Physical properties

The physical properties of acids often provide a clue to their character. Acids can exist in three forms: solid, liquid and gaseous. For example: nitric (HNO3) and sulfuric acid (H2SO4) are colorless liquids; boric (H3BO3) and metaphosphoric (HPO3) are solid acids. Some of them have color and smell. Different acids dissolve differently in water. There are also insoluble ones: H2SiO3 - silicon. Liquid substances have a sour taste. The name of some acids was given by the fruits in which they are found: malic acid, citric acid. Others got their name from the chemical elements contained in them.

Acid classification

Usually acids are classified according to several criteria. The very first is, according to the oxygen content in them. Namely: oxygen-containing (HClO4 - chlorine) and anoxic (H2S - hydrogen sulfide).

By the number of hydrogen atoms (by basicity):

• Monobasic - contains one hydrogen atom (HMnO4);
• Dibasic - has two hydrogen atoms (H2CO3);
• Tribasic, respectively, have three hydrogen atoms (H3BO);
• Polybasic - have four or more atoms, are rare (H4P2O7).

According to the classes of chemical compounds, they are divided into organic and inorganic acids. The former are mainly found in plant products: acetic, lactic, nicotinic, ascorbic acids. Inorganic acids include: sulfuric, nitric, boric, arsenic. The range of their application is quite wide from industrial needs (production of dyes, electrolytes, ceramics, fertilizers, etc.) to cooking or cleaning sewers. Acids can also be classified according to strength, volatility, stability and solubility in water.

Chemical properties

Consider the basic chemical properties of acids.

• The first is interaction with indicators. As indicators, litmus, methyl orange, phenolphthalein and universal indicator paper are used. In acid solutions, the color of the indicator will change color: litmus and universal ind. paper will turn red, methyl orange - pink, phenolphthalein will remain colorless.
• The second is the interaction of acids with bases. This reaction is also called neutralization. The acid reacts with the base, resulting in salt + water. For example: H2SO4+Ca(OH)2=CaSO4+2 H2O.
• Since almost all acids are highly soluble in water, neutralization can be carried out with both soluble and insoluble bases. The exception is silicic acid, which is almost insoluble in water. To neutralize it, bases such as KOH or NaOH are required (they are soluble in water).
• The third is the interaction of acids with basic oxides. This is where the neutralization reaction takes place. Basic oxides are close "relatives" of bases, hence the reaction is the same. We very often use these oxidizing properties of acids. For example, to remove rust from pipes. The acid reacts with the oxide to become a soluble salt.
• The fourth is the reaction with metals. Not all metals react equally well with acids. They are divided into active (K, Ba, Ca, Na, Mg, Al, Mn, Zn, Cr, Fe, Ni, Sn. Pb) and inactive (Cu, Hg, Ag, Pt, Au). It is also worth paying attention to the strength of the acid (strong, weak). For example, hydrochloric and sulfuric acids are able to react with all inactive metals, while citric and oxalic acids are so weak that they react very slowly even with active metals.
• The fifth is the reaction of oxygen-containing acids to heating. Almost all acids of this group, when heated, decompose into oxygen oxide and water. The exceptions are carbonic (H3PO4) and sulfurous acids (H2SO4). When heated, they decompose into water and gas. This must be remembered. That's all the basic properties of acids.

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 may consist of one atom (-Cl, -Br, -I) - these are simple acid residues, and may - 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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7. Acids. Salt. Relationship between classes of inorganic substances

7.1. acids

Acids are electrolytes, during the dissociation of which only hydrogen cations H + are formed as positively charged ions (more precisely, hydronium ions H 3 O +).

Another definition: acids are complex substances consisting of a hydrogen atom and acid residues (Table 7.1).

Table 7.1

Formulas and names of some acids, acid residues and salts

Under normal conditions, acids can be solids (H 3 PO 4 , H 3 BO 3 , H 2 SiO 3 ) and liquids (HNO 3 , H 2 SO 4 , CH 3 COOH). These acids can exist both in individual (100% form) and in the form of dilute and concentrated solutions. For example, H 2 SO 4 , HNO 3 , H 3 PO 4 , CH 3 COOH are known both individually and in solutions.

A number of acids are known only in solutions. These are all hydrohalic (HCl, HBr, HI), hydrogen sulfide H 2 S, hydrocyanic (hydrocyanic HCN), coal H 2 CO 3, sulfurous H 2 SO 3 acid, which are solutions of gases in water. For example, hydrochloric acid is a mixture of HCl and H 2 O, coal is a mixture of CO 2 and H 2 O. It is clear that using the expression "hydrochloric acid solution" is wrong.

Most acids are soluble in water, silicic acid H 2 SiO 3 is insoluble. The vast majority of acids have a molecular structure. Examples of structural formulas of acids:

In most oxygen-containing acid molecules, all hydrogen atoms are bonded to oxygen. But there are exceptions:

Acids are classified according to a number of features (Table 7.2).

Table 7.2

Acid classification

All the general chemical properties of acids are due to the presence in their aqueous solutions of an excess of hydrogen cations H + (H 3 O +).

1. Due to an excess of H + ions, aqueous solutions of acids change the color of violet and methyl orange litmus to red (phenolphthalein does not change color, remains colorless). In an aqueous solution of weak carbonic acid, the litmus is not red, but pink; a solution over a precipitate of very weak silicic acid does not change the color of the indicators at all.

2. Acids interact with basic oxides, bases and amphoteric hydroxides, ammonia hydrate (see Ch. 6).

Example 7.1. To carry out the transformation BaO → BaSO 4, you can use: a) SO 2; b) H 2 SO 4; c) Na 2 SO 4; d) SO3.

Solution. The transformation can be carried out using H 2 SO 4:

BaO + H 2 SO 4 \u003d BaSO 4 ↓ + H 2 O

BaO + SO 3 = BaSO 4

Na 2 SO 4 does not react with BaO, and in the reaction of BaO with SO 2 barium sulfite is formed:

BaO + SO 2 = BaSO 3

Answer: 3).

3. Acids react with ammonia and its aqueous solutions to form ammonium salts:

HCl + NH 3 \u003d NH 4 Cl - ammonium chloride;

H 2 SO 4 + 2NH 3 = (NH 4) 2 SO 4 - ammonium sulfate.

4. Non-oxidizing acids with the formation of a salt and the release of hydrogen react with metals located in the row of activity to hydrogen:

H 2 SO 4 (diff) + Fe = FeSO 4 + H 2

2HCl + Zn \u003d ZnCl 2 \u003d H 2

The interaction of oxidizing acids (HNO 3 , H 2 SO 4 (conc)) with metals is very specific and is considered in the study of the chemistry of elements and their compounds.

5. Acids interact with salts. The reaction has a number of features:

a) in most cases, when a stronger acid reacts with a salt of a weaker acid, a salt of a weak acid is formed and a weak acid, or, as they say, a stronger acid displaces a weaker one. The series of decreasing strength of acids looks like this:

Examples of ongoing reactions:

2HCl + Na 2 CO 3 \u003d 2NaCl + H 2 O + CO 2

H 2 CO 3 + Na 2 SiO 3 = Na 2 CO 3 + H 2 SiO 3 ↓

2CH 3 COOH + K 2 CO 3 \u003d 2CH 3 COOK + H 2 O + CO 2

3H 2 SO 4 + 2K 3 PO 4 = 3K 2 SO 4 + 2H 3 PO 4

Do not interact with each other, for example, KCl and H 2 SO 4 (diff), NaNO 3 and H 2 SO 4 (diff), K 2 SO 4 and HCl (HNO 3, HBr, HI), K 3 PO 4 and H 2 CO 3 , CH 3 COOK and H 2 CO 3 ;

b) in some cases, a weaker acid displaces a stronger one from the salt:

CuSO 4 + H 2 S \u003d CuS ↓ + H 2 SO 4

3AgNO 3 (razb) + H 3 PO 4 = Ag 3 PO 4 ↓ + 3HNO 3.

Such reactions are possible when the precipitates of the resulting salts do not dissolve in the resulting dilute strong acids (H 2 SO 4 and HNO 3);

c) in the case of the formation of precipitates that are insoluble in strong acids, a reaction between a strong acid and a salt formed by another strong acid is possible:

BaCl 2 + H 2 SO 4 \u003d BaSO 4 ↓ + 2HCl

Ba(NO 3) 2 + H 2 SO 4 = BaSO 4 ↓ + 2HNO 3

AgNO 3 + HCl = AgCl↓ + HNO 3

Example 7.2. Indicate the series in which the formulas of substances that react with H 2 SO 4 are given (diff).

1) Zn, Al 2 O 3, KCl (p-p); 3) NaNO 3 (p-p), Na 2 S, NaF; 2) Cu (OH) 2, K 2 CO 3, Ag; 4) Na 2 SO 3, Mg, Zn (OH) 2.

Solution. All substances of series 4 interact with H 2 SO 4 (razb):

Na 2 SO 3 + H 2 SO 4 \u003d Na 2 SO 4 + H 2 O + SO 2

Mg + H 2 SO 4 \u003d MgSO 4 + H 2

Zn(OH) 2 + H 2 SO 4 = ZnSO 4 + 2H 2 O

In row 1) the reaction with KCl (p-p) is not feasible, in row 2) - with Ag, in row 3) - with NaNO 3 (p-p).

Answer: 4).

6. Concentrated sulfuric acid behaves very specifically in reactions with salts. It is a non-volatile and thermally stable acid, therefore it displaces all strong acids from solid (!) Salts, since they are more volatile than H 2 SO 4 (conc):

KCl (tv) + H 2 SO 4 (conc) KHSO 4 + HCl

2KCl (tv) + H 2 SO 4 (conc) K 2 SO 4 + 2HCl

Salts formed by strong acids (HBr, HI, HCl, HNO 3, HClO 4) react only with concentrated sulfuric acid and only in the solid state

Example 7.3. Concentrated sulfuric acid, unlike dilute sulfuric acid, reacts:

3) KNO 3 (TV);

Solution. Both acids react with KF, Na 2 CO 3 and Na 3 PO 4, and only H 2 SO 4 (conc) react with KNO 3 (tv).

Answer: 3).

Methods for obtaining acids are very diverse.

Anoxic acids receive:

• by dissolving the corresponding gases in water:

HCl (g) + H 2 O (g) → HCl (p-p)

H 2 S (g) + H 2 O (g) → H 2 S (solution)

• from salts by displacement by stronger or less volatile acids:

FeS + 2HCl \u003d FeCl 2 + H 2 S

KCl (tv) + H 2 SO 4 (conc) = KHSO 4 + HCl

Na 2 SO 3 + H 2 SO 4 Na 2 SO 4 + H 2 SO 3

oxygenated acids receive:

• by dissolving the corresponding acid oxides in water, while the oxidation state of the acid-forming element in the oxide and acid remains the same (NO 2 is an exception):

N 2 O 5 + H 2 O \u003d 2HNO 3

SO 3 + H 2 O \u003d H 2 SO 4

P 2 O 5 + 3H 2 O 2H 3 PO 4

• oxidation of non-metals with oxidizing acids:

S + 6HNO 3 (conc) = H 2 SO 4 + 6NO 2 + 2H 2 O

• by displacing a strong acid from a salt of another strong acid (if a precipitate forms that is insoluble in the resulting acids):

Ba (NO 3) 2 + H 2 SO 4 (razb) \u003d BaSO 4 ↓ + 2HNO 3

AgNO 3 + HCl = AgCl↓ + HNO 3

• displacement of a volatile acid from its salts by a less volatile acid.

For this purpose, non-volatile thermally stable concentrated sulfuric acid is most often used:

NaNO 3 (tv) + H 2 SO 4 (conc) NaHSO 4 + HNO 3

KClO 4 (tv) + H 2 SO 4 (conc) KHSO 4 + HClO 4

• by displacing a weaker acid from its salts with a stronger acid:

Ca 3 (PO 4) 2 + 3H 2 SO 4 = 3CaSO 4 ↓ + 2H 3 PO 4

NaNO 2 + HCl = NaCl + HNO 2

K 2 SiO 3 + 2HBr = 2KBr + H 2 SiO 3 ↓

Acids can be classified according to different criteria:

1) The presence of oxygen atoms in the acid

2) Acid basicity

The basicity of an acid is the number of "mobile" hydrogen atoms in its molecule, capable of splitting off from the acid molecule in the form of hydrogen cations H + during dissociation, and also being replaced by metal atoms:

4) Solubility

5) Sustainability

7) Oxidizing properties

Chemical properties of acids

1. Ability to dissociate

Acids dissociate in aqueous solutions into hydrogen cations and acid residues. As already mentioned, acids are divided into well-dissociating (strong) and low-dissociating (weak). When writing the dissociation equation for strong monobasic acids, either one arrow pointing to the right () or an equal sign (=) is used, which actually shows the irreversibility of such dissociation. For example, the dissociation equation for strong hydrochloric acid can be written in two ways:

or in this form: HCl \u003d H + + Cl -

or in this: HCl → H + + Cl -

In fact, the direction of the arrow tells us that the reverse process of combining hydrogen cations with acidic residues (association) in strong acids practically does not occur.

In case we want to write the equation for the dissociation of a weak monobasic acid, we must use two arrows instead of the sign in the equation. This sign reflects the reversibility of the dissociation of weak acids - in their case, the reverse process of combining hydrogen cations with acidic residues is strongly pronounced:

CH 3 COOH CH 3 COO - + H +

Polybasic acids dissociate in steps, i.e. hydrogen cations are not detached from their molecules simultaneously, but in turn. For this reason, the dissociation of such acids is expressed not by one, but by several equations, the number of which is equal to the basicity of the acid. For example, the dissociation of tribasic phosphoric acid proceeds in three steps with the successive detachment of H + cations:

H 3 PO 4 H + + H 2 PO 4 —

H 2 PO 4 - H + + HPO 4 2-

HPO 4 2- H + + PO 4 3-

It should be noted that each next stage of dissociation proceeds to a lesser extent than the previous one. That is, H 3 PO 4 molecules dissociate better (to a greater extent) than H 2 PO 4 — ions, which, in turn, dissociate better than HPO 4 2- ions. This phenomenon is associated with an increase in the charge of acidic residues, as a result of which the strength of the bond between them and positive H + ions increases.

Of the polybasic acids, sulfuric acid is an exception. Since this acid dissociates well in both steps, it is permissible to write the equation of its dissociation in one stage:

H 2 SO 4 2H + + SO 4 2-

2. Interaction of acids with metals

The seventh point in the classification of acids, we indicated their oxidizing properties. It was pointed out that acids are weak oxidizing agents and strong oxidizing agents. The vast majority of acids (practically all except H 2 SO 4 (conc.) and HNO 3) are weak oxidizing agents, since they can show their oxidizing ability only due to hydrogen cations. Such acids can oxidize from metals only those that are in the activity series to the left of hydrogen, while the salt of the corresponding metal and hydrogen are formed as products. For example:

H 2 SO 4 (diff.) + Zn ZnSO 4 + H 2

2HCl + Fe FeCl 2 + H 2

As for strong oxidizing acids, i.e. H 2 SO 4 (conc.) and HNO 3, then the list of metals on which they act is much wider, and it includes both all metals up to hydrogen in the activity series, and almost everything after. That is, concentrated sulfuric acid and nitric acid of any concentration, for example, will oxidize even such inactive metals as copper, mercury, and silver. In more detail, the interaction of nitric acid and concentrated sulfuric acid with metals, as well as some other substances due to their specificity, will be considered separately at the end of this chapter.

3. Interaction of acids with basic and amphoteric oxides

Acids react with basic and amphoteric oxides. Silicic acid, since it is insoluble, does not react with low-active basic oxides and amphoteric oxides:

H 2 SO 4 + ZnO ZnSO 4 + H 2 O

6HNO 3 + Fe 2 O 3 2Fe (NO 3) 3 + 3H 2 O

H 2 SiO 3 + FeO ≠

4. Interaction of acids with bases and amphoteric hydroxides

HCl + NaOH H2O + NaCl

3H 2 SO 4 + 2Al (OH) 3 Al 2 (SO 4) 3 + 6H 2 O

5. Interaction of acids with salts

This reaction proceeds if a precipitate, a gas, or a substantially weaker acid than the one that reacts is formed. For example:

H 2 SO 4 + Ba(NO 3) 2 BaSO 4 ↓ + 2HNO 3

CH 3 COOH + Na 2 SO 3 CH 3 COONa + SO 2 + H 2 O

HCOONa + HCl HCOOH + NaCl

6. Specific oxidizing properties of nitric and concentrated sulfuric acids

As mentioned above, nitric acid in any concentration, as well as sulfuric acid exclusively in a concentrated state, are very strong oxidizing agents. In particular, unlike other acids, they oxidize not only metals that are up to hydrogen in the activity series, but also almost all metals after it (except platinum and gold).

For example, they are able to oxidize copper, silver and mercury. However, it should be firmly grasped the fact that a number of metals (Fe, Cr, Al), despite the fact that they are quite active (they are up to hydrogen), nevertheless, do not react with concentrated HNO 3 and concentrated H 2 SO 4 without heating on due to the passivation phenomenon - a protective film of solid oxidation products is formed on the surface of such metals, which does not allow molecules of concentrated sulfuric and concentrated nitric acids to penetrate deep into the metal for the reaction to proceed. However, with strong heating, the reaction still proceeds.

In the case of interaction with metals, the required products are always the salt of the corresponding metal and the acid used, as well as water. A third product is also always isolated, the formula of which depends on many factors, in particular, such as the activity of metals, as well as the concentration of acids and the temperature of the reactions.

The high oxidizing power of concentrated sulfuric and concentrated nitric acids allows them to react not only with practically all metals of the activity range, but even with many solid non-metals, in particular, with phosphorus, sulfur, and carbon. The table below clearly shows the products of the interaction of sulfuric and nitric acids with metals and non-metals, depending on the concentration:

7. Reducing properties of anoxic acids

All anoxic acids (except HF) can exhibit reducing properties due to the chemical element that is part of the anion, under the action of various oxidizing agents. So, for example, all hydrohalic acids (except HF) are oxidized by manganese dioxide, potassium permanganate, potassium dichromate. In this case, halide ions are oxidized to free halogens:

4HCl + MnO 2 MnCl 2 + Cl 2 + 2H 2 O

18HBr + 2KMnO 4 2KBr + 2MnBr 2 + 8H 2 O + 5Br 2

14НI + K 2 Cr 2 O 7 3I 2 ↓ + 2Crl 3 + 2KI + 7H 2 O

Among all hydrohalic acids, hydroiodic acid has the greatest reducing activity. Unlike other hydrohalic acids, even ferric oxide and salts can oxidize it.

6HI ​​+ Fe 2 O 3 2FeI 2 + I 2 ↓ + 3H 2 O

2HI + 2FeCl 3 2FeCl 2 + I 2 ↓ + 2HCl

Hydrosulfide acid H 2 S also has a high reducing activity. Even an oxidizing agent such as sulfur dioxide can oxidize it.