1. Bases interact with acids to form salt and water:

Cu(OH) 2 + 2HCl = CuCl 2 + 2H 2 O

2. C acid oxides, forming salt and water:

Ca(OH) 2 + CO 2 = CaCO 3 + H 2 O

3. Alkalis react with amphoteric oxides and hydroxides, forming salt and water:

2NaOH + Cr 2 O 3 \u003d 2NaCrO 2 + H 2 O

KOH + Cr(OH) 3 = KCrO 2 + 2H 2 O

4. Alkalis interact with soluble salts, forming either a weak base, or a precipitate, or a gas:

2NaOH + NiCl 2 \u003d Ni (OH) 2 ¯ + 2NaCl

base

2KOH + (NH 4) 2 SO 4 \u003d 2NH 3 + 2H 2 O + K 2 SO 4

Ba(OH) 2 + Na 2 CO 3 = BaCO 3 ¯ + 2NaOH

5. Alkalis react with some metals, which correspond to amphoteric oxides:

2NaOH + 2Al + 6H 2 O = 2Na + 3H 2

6. The action of alkali on the indicator:

Oh - + phenolphthalein ® raspberry color

Oh - + litmus ® Blue colour

7. Decomposition of some bases when heated:

Сu(OH) 2 ® CuO + H 2 O

Amphoteric hydroxides – chemical compounds that exhibit the properties of both bases and acids. Amphoteric hydroxides correspond to amphoteric oxides (see section 3.1).

Amphoteric hydroxides are usually written in the form of a base, but they can also be represented as an acid:

Zn(OH) 2 Û H 2 ZnO 2

base to

Chemical properties of amphoteric hydroxides

1. Amphoteric hydroxides interact with acids and acid oxides:

Be(OH) 2 + 2HCl = BeCl 2 + 2H 2 O

Be(OH) 2 + SO 3 = BeSO 4 + H 2 O

2. Interact with alkalis and basic oxides of alkali and alkaline earth metals:

Al(OH) 3 + NaOH = NaAlO 2 + 2H 2 O;

H 3 AlO 3 acid sodium metaaluminate

(H 3 AlO 3 ® HAlO 2 + H 2 O)

2Al(OH) 3 + Na 2 O = 2NaAlO 2 + 3H 2 O

All amphoteric hydroxides are weak electrolytes.

salt

salt- This complex substances, consisting of metal ions and an acid residue. Salts are products of complete or partial replacement of hydrogen ions by metal (or ammonium) ions in acids. Types of salts: medium (normal), acid and basic.

Medium salts- these are products of complete replacement of hydrogen cations in acids with metal (or ammonium) ions: Na 2 CO 3, NiSO 4, NH 4 Cl, etc.

Chemical properties of medium salts

1. Salts interact with acids, alkalis and other salts, forming either a weak electrolyte or a precipitate; or gas:

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

Na 2 SO 4 + Ba(OH) 2 = BaSO 4 ¯ + 2NaOH

CaCl 2 + 2AgNO 3 \u003d 2AgCl¯ + Ca (NO 3) 2

2CH 3 COONa + H 2 SO 4 = Na 2 SO 4 + 2CH 3 COOH

NiSO 4 + 2KOH \u003d Ni (OH) 2 ¯ + K 2 SO 4

base

NH 4 NO 3 + NaOH \u003d NH 3 + H 2 O + NaNO 3

2. Salts interact with more active metals. A more active metal displaces a less active metal from a salt solution (Appendix 3).

Zn + CuSO 4 \u003d ZnSO 4 + Cu

Acid salts- these are products of incomplete replacement of hydrogen cations in acids with metal (or ammonium) ions: NaHCO 3, NaH 2 PO 4, Na 2 HPO 4, etc. Acid salts can only be formed by polybasic acids. Almost all acidic salts are highly soluble in water.

Obtaining acid salts and converting them into medium

1. Acid salts are obtained by reacting an excess of acid or acid oxide with a base:

H 2 CO 3 + NaOH = NaHCO 3 + H 2 O

CO 2 + NaOH = NaHCO 3

2. When an excess of acid interacts with a basic oxide:

2H 2 CO 3 + CaO \u003d Ca (HCO 3) 2 + H 2 O

3. Acid salts are obtained from medium salts by adding acid:

eponymous

Na 2 SO 3 + H 2 SO 3 \u003d 2NaHSO 3;

Na 2 SO 3 + HCl \u003d NaHSO 3 + NaCl

4. Acid salts are converted to medium using alkali:

NaHCO 3 + NaOH = Na 2 CO 3 + H 2 O

Basic salts are products of incomplete substitution of hydroxo groups (OH - ) bases with an acidic residue: MgOHCl, AlOHSO 4, etc. Basic salts can only be formed by weak bases of polyvalent metals. These salts are generally sparingly soluble.

Obtaining basic salts and converting them to medium

1. Basic salts are obtained by reacting an excess of a base with an acid or acid oxide:

Mg(OH) 2 + HCl = MgOHCl¯ + H 2 O

hydroxo-

magnesium chloride

Fe(OH) 3 + SO 3 = FeOHSO 4 ¯ + H 2 O

hydroxo-

iron(III) sulfate

2. Basic salts are formed from an average salt by adding a lack of alkali:

Fe 2 (SO 4) 3 + 2NaOH \u003d 2FeOHSO 4 + Na 2 SO 4

3. Basic salts are converted to medium ones by adding an acid (preferably the one that corresponds to the salt):

MgOHCl + HCl \u003d MgCl 2 + H 2 O

2MgOHCl + H 2 SO 4 \u003d MgCl 2 + MgSO 4 + 2H 2 O


ELECTROLYTES

electrolytes- these are substances that decompose into ions in solution under the influence of polar solvent molecules (H 2 O). According to the ability to dissociate (decay into ions), electrolytes are conditionally divided into strong and weak. Strong electrolytes dissociate almost completely (in dilute solutions), while weak ones decompose into ions only partially.

Strong electrolytes include:

strong acids (see p. 20);

strong bases - alkalis (see p. 22);

almost all soluble salts.

Weak electrolytes include:

Weak acids (see p. 20);

bases are not alkalis;

One of the main characteristics of a weak electrolyte is dissociation constant – TO . For example, for a monobasic acid,

HA Û H + + A - ,

where, is the equilibrium concentration of H + ions;

is the equilibrium concentration of acid anions A - ;

is the equilibrium concentration of acid molecules,

Or for a weak foundation,

MOH Û M + +OH - ,

,

where, is the equilibrium concentration of cations M + ;

– equilibrium concentration of hydroxide ions OH - ;

is the equilibrium concentration of weak base molecules.

Dissociation constants of some weak electrolytes (at t = 25°С)

Substance TO Substance TO
HCOOH K = 1.8×10 -4 H3PO4 K 1 \u003d 7.5 × 10 -3
CH3COOH K = 1.8×10 -5 K 2 \u003d 6.3 × 10 -8
HCN K = 7.9×10 -10 K 3 \u003d 1.3 × 10 -12
H2CO3 K 1 \u003d 4.4 × 10 -7 HClO K = 2.9×10 -8
K 2 \u003d 4.8 × 10 -11 H3BO3 K 1 \u003d 5.8 × 10 -10
HF K = 6.6×10 -4 K 2 \u003d 1.8 × 10 -13
HNO 2 K = 4.0×10 -4 K 3 \u003d 1.6 × 10 -14
H2SO3 K 1 \u003d 1.7 × 10 -2 H2O K = 1.8×10 -16
K 2 \u003d 6.3 × 10 -8 NH 3 × H 2 O K = 1.8×10 -5
H 2 S K 1 \u003d 1.1 × 10 -7 Al(OH)3 K 3 \u003d 1.4 × 10 -9
K 2 \u003d 1.0 × 10 -14 Zn(OH) 2 K 1 \u003d 4.4 × 10 -5
H2SiO3 K 1 \u003d 1.3 × 10 -10 K 2 \u003d 1.5 × 10 -9
K 2 \u003d 1.6 × 10 -12 Cd(OH)2 K 2 \u003d 5.0 × 10 -3
Fe(OH)2 K 2 \u003d 1.3 × 10 -4 Cr(OH)3 K 3 \u003d 1.0 × 10 -10
Fe(OH)3 K 2 \u003d 1.8 × 10 -11 Ag(OH) K = 1.1×10 -4
K 3 \u003d 1.3 × 10 -12 Pb(OH)2 K 1 \u003d 9.6 × 10 -4
Cu(OH)2 K 2 \u003d 3.4 × 10 -7 K 2 \u003d 3.0 × 10 -8
Ni(OH)2 K 2 \u003d 2.5 × 10 -5

salts complex substances are called, the molecules of which consist of metal atoms and acid residues (sometimes they may contain hydrogen). For example, NaCl is sodium chloride, CaSO 4 is calcium sulfate, etc.

Practically All salts are ionic compounds therefore, in salts, ions of acid residues and metal ions are interconnected:

Na + Cl - - sodium chloride

Ca 2+ SO 4 2– - calcium sulfate, etc.

Salt is a product of partial or complete replacement of acid hydrogen atoms by a metal. Hence, the following types of salts are distinguished:

1. Medium salts- all hydrogen atoms in the acid are replaced by a metal: Na 2 CO 3, KNO 3, etc.

2. Acid salts- not all hydrogen atoms in the acid are replaced by a metal. Of course, acid salts can only form dibasic or polybasic acids. Monobasic acids cannot give acid salts: NaHCO 3, NaH 2 PO 4, etc. d.

3. Double salts- hydrogen atoms of a dibasic or polybasic acid are replaced not by one metal, but by two different ones: NaKCO 3, KAl(SO 4) 2, etc.

4. Basic salts can be considered as products of incomplete or partial substitution of hydroxyl groups of bases by acidic residues: Al(OH)SO 4 , Zn(OH)Cl, etc.

According to international nomenclature, the name of the salt of each acid comes from the Latin name of the element. For example, salts of sulfuric acid are called sulfates: CaSO 4 - calcium sulfate, Mg SO 4 - magnesium sulfate, etc.; salt of hydrochloric acid are called chlorides: NaCl - sodium chloride, ZnCI 2 - zinc chloride, etc.

The particle "bi" or "hydro" is added to the name of salts of dibasic acids: Mg (HCl 3) 2 - magnesium bicarbonate or bicarbonate.

Provided that in a tribasic acid only one hydrogen atom is replaced by a metal, then the prefix "dihydro" is added: NaH 2 PO 4 - sodium dihydrogen phosphate.

Salts are solid substances that have a wide range of solubility in water.

Chemical properties of salts

The chemical properties of salts are determined by the properties of the cations and anions that are part of their composition.

1. Some salts decompose when calcined:

CaCO 3 \u003d CaO + CO 2

2. React with acids to form a new salt and a new acid. For this reaction to occur, it is necessary that the acid be stronger than the salt that the acid acts on:

2NaCl + H 2 SO 4 → Na 2 SO 4 + 2HCl.

3. Interact with bases, forming a new salt and a new base:

Ba(OH) 2 + MgSO 4 → BaSO 4 ↓ + Mg(OH) 2 .

4. Interact with each other with the formation of new salts:

NaCl + AgNO 3 → AgCl + NaNO 3 .

5. Interact with metals, which are in the range of activity to the metal that is part of the salt:

Fe + CuSO 4 → FeSO 4 + Cu↓.

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Foundations

Bases are compounds that contain only the hydroxide of OH ions as an anions. The number of hydroxide ions that can be replaced by an acid residue determines the acidity of the base. In this regard, the bases are one-, two- and polyacid, however, one- and two-acid ones are most often referred to as true bases. Among them, water-soluble and water-insoluble bases should be distinguished. Note that water-soluble and almost completely dissociating bases are called alkalis (strong electrolytes). These include hydroxides of alkaline and alkaline earth elements and in no case a solution of ammonia in water.

The name of the base begins with the word hydroxide, after which in genitive case is given Russian name cation, and its charge is indicated in parentheses. It is allowed to list the number of hydroxide ions using the prefixes di-, tri-, tetra. For example: Mn (OH) 3 - manganese (III) hydroxide or manganese trihydroxide.

Note that between bases and basic oxides there is genetic connection: basic oxides correspond to bases. Therefore, base cations most often have a charge of one or two, which corresponds to the lowest oxidation states of metals.

Remember the basic ways to get reasons

1. Interaction of active metals with water:

2Na + 2H 2 O \u003d 2NaOH + H 2

La + 6H 2 O \u003d 2La (OH) 3 + 3H 2

Interaction of basic oxides with water:

CaO + H 2 O \u003d Ca (OH) 2

MgO + H 2 O \u003d Mg (OH) 2.

3. Interaction of salts with alkalis:

МnSO 4 + 2KOH \u003d Mn (OH) 2 ↓ + K 2 SO 4

NH 4 C1 + NaOH \u003d NaCl + NH 3 ∙ H 2 O

Na 2 CO 3 + Ca (OH) 2 \u003d 2NaOH + CaCO 3

MgOHCl + NaOH \u003d Mg (OH) 2 + NaCl.

Electrolysis of aqueous solutions of salts with a diaphragm:

2NaCl + 2H 2 O → 2NaOH + Cl 2 + H 2

Please note that in paragraph 3, the starting reagents must be selected in such a way that among the reaction products there is either a sparingly soluble compound or a weak electrolyte.

Note that when considering the chemical properties of bases, the reaction conditions depend on the solubility of the base.

1. Interaction with acids:

NaOH + H 2 SO 4 \u003d NaHSO 4 + H 2 O

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

2Mg(OH) 2 + H 2 SO 4 = (MgOH) 2 SO 4 + 2H 2 O

Mg(OH) 2 + H 2 SO 4 = MgSO 4 + 2H 2 O

Mg (OH) 2 + 2H 2 SO 4 \u003d Mg (HSO 4) 2 + 2H 2 O

2. Interaction with acid oxides:

NaOH + CO 2 \u003d NaHCO 3

2NaOH + CO 2 \u003d Na 2 CO 3 + H 2 O

Fe (OH) 2 + P 2 O 5 \u003d Fe (PO 3) 2 + H 2 O

ZFe (OH) 2 + P 2 O 5 \u003d Fe 3 (PO 4) 2 + 2H 2 O

3. Interaction with amphoteric oxides:

A1 2 O 3 + 2NaOH p + 3H 2 O \u003d 2Na

Al 2 O 3 + 2NaOH T \u003d 2NaAlO 2 + H 2 O


Cr 2 O 3 + Mg (OH) 2 \u003d Mg (CrO 2) 2 + H 2 O

4. Interaction with amfteric hydroxides:

Ca (OH) 2 + 2Al (OH) 3 \u003d Ca (AlO 2) 2 + 4H 2 O

3NaOH + Cr(OH) 3 = Na 3

interaction with salts.

To the reactions described in paragraph 3 of the preparation methods, one should add:

2ZnSO 4 + 2KOH = (ZnOH) 2 S0 4 + K 2 SO 4

NaHCO 3 + NaOH \u003d Na 2 CO 3 + H 2 O

BeSO 4 + 4NaOH \u003d Na 2 + Na 2 SO 4

Cu(OH) 2 + 4NH 3 ∙H 2 O \u003d (OH) 2 + 4H 2 O

6. Oxidation to amphoteric hydroxides or salts:

4Fe(OH) 2 + O 2 + 2H 2 O = 4Fe(OH) 3

2Cr(OH) 2 + 2H 2 O + Na 2 O 2 + 4NaOH = 2Na 3.

7. Decomposition when heated:

Ca (OH) 2 \u003d CaO + H 2 O.

Please note that hydroxides alkali metals, except for lithium, do not participate in such reactions.

!!!Are there alkaline precipitation?!!! Yes, there are, but they are not as common as acid rain, are little known, and their influence on objects environment practically unexplored. Nevertheless, their consideration deserves attention.

The origin of alkaline precipitation can be explained as follows.

CaCO 3 →CaO + CO 2

In the atmosphere, calcium oxide combines with water vapor during their condensation, with rain or sleet, forming calcium hydroxide:

CaO + H 2 O → Ca (OH) 2,

which creates an alkaline reaction precipitation. In the future, the interaction of calcium hydroxide with carbon dioxide and water is possible with the formation of calcium carbonate and calcium bicarbonate:

Ca (OH) 2 + CO 2 → CaCO 3 + H 2 O;

CaCO 3 + CO 2 + H 2 O → Ca (HC0 3) 2.

Chemical analysis rainwater showed that it contains small amounts of sulfate and nitrate ions (about 0.2 mg/l). Sulfuric and nitric acids are known to cause acidic precipitation. At the same time, it is observed great content calcium cations (5-8 mg/l) and bicarbonate ions, the content of which in the area of ​​the enterprises of the construction complex is 1.5-2 times higher than in other parts of the city, and is 18-24 mg/l. This shows that in the formation of local alkaline precipitation leading role plays the calcium carbonate system and the processes occurring in it, as mentioned above.

Alkaline precipitation affects plants, changes in the phenotypic structure of plants are noted. There are traces of "burns" on leaf blades, white coating on the leaves and the oppressed state of herbaceous plants.

Every day we encounter salts and do not even think about the role they play in our lives. But without them, water would not be so tasty, and food would not bring pleasure, and plants would not grow, and life on earth could not exist if there were no salt in our world. So what are these substances and what properties of salts make them indispensable?

What are salts

In its composition, this is the most numerous class, characterized by diversity. Back in the 19th century, the chemist J. Verzelius defined salt as the product of a reaction between an acid and a base, in which the hydrogen atom is replaced by a metal one. In water, salts usually dissociate into a metal or ammonium (cation) and an acid residue (anion).

You can get salt in the following ways:

  • by the interaction of metal and non-metal, in this case it will be oxygen-free;
  • when a metal reacts with an acid, a salt is obtained and hydrogen is released;
  • a metal can displace another metal from solution;
  • when two oxides interact - acidic and basic (they are also called non-metal oxide and metal oxide, respectively);
  • the reaction of metal oxide and acid produces salt and water;
  • the reaction between a base and a non-metal oxide also produces salt and water;
  • using an ion exchange reaction, in this case, various water-soluble substances (bases, acids, salts) can react, but the reaction will proceed if gas, water or slightly soluble (insoluble) salts in water are formed.

Only from chemical composition properties of salts and depend. But first, let's look at their classes.

Classification

Depending on the composition, the following classes of salts are distinguished:

  • by oxygen content (oxygen-containing and anoxic);
  • by interaction with water (soluble, slightly soluble and insoluble).

This classification does not fully reflect the diversity of substances. Modern and most full classification, reflecting not only the composition, but also the properties of salts, is presented in the following table.

salt
NormalSourMainDoublemixedComplex
Hydrogen is completely replacedHydrogen atoms are not completely replaced by metalBase groups are not completely replaced by an acid residueComposed of two metals and one acid residueOne metal and two acid residuesCompound substances consisting of a complex cation and anion or a cation and a complex anion
NaClKHSO 4FeOHSO3KNaSO 4CaClBrSO 4

Physical properties

No matter how wide the class of these substances, but common physical properties salts can be isolated. These are substances of non-molecular structure, with an ionic crystal lattice.

Very high melting and boiling points. Under normal conditions, all salts do not conduct electricity, but in solution, most of them conduct electricity perfectly.

The color can be very different, it depends on the metal ion that is part of it. Ferrous sulfate (FeSO 4) is green, ferrous chloride (FeCl 3) is dark red, and potassium chromate (K 2 CrO 4) is a beautiful bright yellow. But most salts are still colorless or white.

Solubility in water also varies and depends on the composition of the ions. In principle, all physical properties of salts have a singularity. They depend on which metal ion and which acid residue are included in the composition. Let's continue with the salts.

Chemical properties of salts

There is also important feature. Like the physical Chemical properties salts depend on their composition. And also what class they belong to.

But general properties salts can still be distinguished:

  • many of them decompose when heated with the formation of two oxides: acidic and basic, and oxygen-free - metal and non-metal;
  • salts also interact with other acids, but the reaction proceeds only if the salt contains an acidic residue of a weak or volatile acid, or an insoluble salt is obtained as a result;
  • interaction with alkali is possible if the cation forms an insoluble base;
  • possible reaction between the two different salts, but only if one of the newly formed salts does not dissolve in water;
  • a reaction with a metal can also occur, but it is possible only if we take the metal located to the right in the voltage series from the metal contained in the salt.

The chemical properties of salts related to normal are discussed above, while other classes react with substances somewhat differently. But the difference is only in the output products. Basically, all the chemical properties of salts are preserved, as are the requirements for the course of reactions.