Chemical properties of strong acids. The most important classes of inorganic substances

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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Substances that dissociate in solutions to form hydrogen ions are called.

Acids are classified according to their strength, basicity, and the presence or absence of oxygen in the composition of the acid.

By strengthacids are divided into strong and weak. The most important strong acids are nitric HNO 3 , sulfuric H 2 SO 4 , and hydrochloric HCl .

By the presence of oxygen distinguish oxygen-containing acids ( HNO3, H3PO4 etc.) and anoxic acids ( HCl, H 2 S , HCN, etc.).

By basicity, i.e. according to the number of hydrogen atoms in an acid molecule that can be replaced by metal atoms to form a salt, acids are divided into monobasic (for example, HNO 3, HCl), dibasic (H 2 S, H 2 SO 4), tribasic (H 3 PO 4 ), etc.

The names of oxygen-free acids are derived from the name of the non-metal with the addition of the ending -hydrogen: HCl - hydrochloric acid, H 2 S e - hydroselenic acid, HCN - hydrocyanic acid.

The names of oxygen-containing acids are also formed from the Russian name of the corresponding element with the addition of the word "acid". At the same time, the name of the acid in which the element is in the highest oxidation state ends in "naya" or "ova", for example, H2SO4 - sulfuric acid, HClO 4 - perchloric acid, H 3 AsO 4 - arsenic acid. With a decrease in the degree of oxidation of the acid-forming element, the endings change in the following sequence: “oval” ( HClO 3 - chloric acid), "pure" ( HClO 2 - chlorous acid), "wobbly" ( H O Cl - hypochlorous acid). If the element forms acids, being in only two oxidation states, then the name of the acid corresponding to the lowest oxidation state of the element receives the ending "pure" ( HNO3 - Nitric acid, HNO 2 - nitrous acid).

Table - The most important acids and their salts

Obtaining acids

1. Anoxic acids can be obtained by direct combination of non-metals with hydrogen:

H 2 + Cl 2 → 2HCl,

H 2 + S H 2 S.

2. Oxygen-containing acids can often be obtained by directly combining acid oxides with water:

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

CO 2 + H 2 O \u003d H 2 CO 3,

P 2 O 5 + H 2 O \u003d 2 HPO 3.

3. Both oxygen-free and oxygen-containing acids can be obtained by exchange reactions between salts and other acids:

BaBr 2 + H 2 SO 4 \u003d BaSO 4 + 2HBr,

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

CaCO 3 + 2HBr \u003d CaBr 2 + CO 2 + H 2 O.

4. In some cases, redox reactions can be used to obtain acids:

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

3P + 5HNO 3 + 2H 2 O = 3H 3 PO 4 + 5NO.

Chemical properties of acids

1. The most characteristic chemical property of acids is their ability to react with bases (as well as with basic and amphoteric oxides) to form salts, for example:

H 2 SO 4 + 2NaOH \u003d Na 2 SO 4 + 2H 2 O,

2HNO 3 + FeO \u003d Fe (NO 3) 2 + H 2 O,

2 HCl + ZnO \u003d ZnCl 2 + H 2 O.

2. The ability to interact with some metals in the series of voltages up to hydrogen, with the release of hydrogen:

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

2Al + 6HCl \u003d 2AlCl 3 + 3H 2.

3. With salts, if a poorly soluble salt or volatile substance is formed:

H 2 SO 4 + BaCl 2 = BaSO 4 ↓ + 2HCl,

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

2KHCO 3 + H 2 SO 4 \u003d K 2 SO 4 + 2SO 2+ 2H2O.

Note that polybasic acids dissociate in steps, and the ease of dissociation in each of the steps decreases, therefore, for polybasic acids, acid salts are often formed instead of medium salts (in the case of an excess of the reacting acid):

Na 2 S + H 3 PO 4 = Na 2 HPO 4 + H 2 S,

NaOH + H 3 PO 4 = NaH 2 PO 4 + H 2 O.

4. A special case of acid-base interaction is the reaction of acids with indicators, leading to a change in color, which has long been used for the qualitative detection of acids in solutions. So, litmus changes color in an acidic environment to red.

5. When heated, oxygen-containing acids decompose into oxide and water (preferably in the presence of a water-removing P2O5):

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

H 2 SiO 3 \u003d H 2 O + SiO 2.

M.V. Andryukhova, L.N. Borodin

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 ↓

Complex substances consisting of hydrogen atoms and an acidic residue are called mineral or inorganic acids. The acid residue is oxides and non-metals combined with hydrogen. The main property of acids is the ability to form salts.

Classification

The basic formula of mineral acids is H n Ac, where Ac is the acid residue. Depending on the composition of the acid residue, two types of acids are distinguished:

• oxygen containing oxygen;
• oxygen-free, consisting only of hydrogen and non-metal.

The main list of inorganic acids according to the type is presented in the table.

In addition, in accordance with the properties of the acid are classified according to the following criteria:

• solubility: soluble (HNO 3 , HCl) and insoluble (H 2 SiO 3);
• volatility: volatile (H 2 S, HCl) and non-volatile (H 2 SO 4 , H 3 PO 4);
• degree of dissociation: strong (HNO 3) and weak (H 2 CO 3).

Rice. 1. Scheme for the classification of acids.

Traditional and trivial names are used to designate mineral acids. Traditional names correspond to the name of the element that forms the acid with the addition of the morphemic -naya, -ovaya, as well as -pure, -novataya, -novaty to indicate the degree of oxidation.

Receipt

The main methods for obtaining acids are presented in the table.

Properties

Most acids are sour-tasting liquids. Tungsten, chromic, boric and several other acids are in a solid state under normal conditions. Some acids (H 2 CO 3, H 2 SO 3, HClO) exist only in the form of an aqueous solution and are weak acids.

Rice. 2. Chromic acid.

Acids are active substances that react:

• with metals:

  Ca + 2HCl \u003d CaCl 2 + H 2;

• with oxides:

  CaO + 2HCl \u003d CaCl 2 + H 2 O;

• with base:

  H 2 SO 4 + 2KOH \u003d K 2 SO 4 + 2H 2 O;

• with salts:

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

All reactions are accompanied by the formation of salts.

A qualitative reaction is possible with a change in the color of the indicator:

• litmus turns red;
• methyl orange - in pink;
• phenolphthalein does not change.

Rice. 3. Colors of indicators during acid interaction.

The chemical properties of mineral acids are determined by the ability to dissociate in water with the formation of hydrogen cations and anions of hydrogen residues. Acids that react with water irreversibly (dissociate completely) are called strong acids. These include chlorine, nitrogen, sulfuric and hydrochloric.

What have we learned?

Inorganic acids are formed by hydrogen and an acidic residue, which are non-metal atoms or an oxide. Depending on the nature of the acid residue, acids are classified into anoxic and oxygen-containing. All acids have a sour taste and are able to dissociate in an aqueous medium (decompose into cations and anions). Acids are obtained from simple substances, oxides, salts. When interacting with metals, oxides, bases, salts, acids form salts.

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