4. Classification, preparation and properties of salts

The most complex among inorganic compounds are salts. They are very diverse in composition. They are divided into medium, sour, basic, double, complex, mixed.

Salts are compounds that, when dissociated in an aqueous solution, form positively charged metal ions and negatively charged ions of acid residues, and sometimes, in addition to them, hydrogen ions and hydroxide ions.

Salts can be considered as products of substitution of hydrogen atoms in an acid by metal atoms (or groups of atoms):

H 2 SO 4 → NaHSO 4 → Na 2 SO 4,

Or as products of substitution of hydroxo groups mainly by hydroxide acid residues:

Zn (OH) 2 → ZnOHCl → ZnCl 2.

With complete substitution, we get medium (or normal) salts:

Ca (OH) 2 + H 2 SO 4 \u003d CaSO 4 + 2H 2 O.

When the middle salts are dissolved, metal cations and anions of the acid residue are formed:

Na 2 SO 4 →2 Na + + SO 4 2 -.

With incomplete replacement of hydrogen, acids are obtained acid salts:

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

When acid salts are dissolved in a solution, metal cations, complex anions of the acid residue, as well as ions that are products of the dissociation of this complex residue, including H + ions, are formed:

NaHCO 3 →Na + + HCO 3 -

HCO3- H + + CO 3 2 - .

With incomplete substitution of hydroxo groups of the base - basic salts:

Mg (OH) 2 + HBr \u003d Mg (OH) Br + H 2 O.

When basic salts are dissolved in solution, acid anions and complex cations are formed, consisting of a metal and hydroxo groups. These complex cations are also capable of dissociation. Therefore, OH ions are present in a basic salt solution. - :

Mg(OH)Br → (MgOH) + + Br - ,

(MgOH) + Mg 2+ + OH -.

Thus, in accordance with this definition, salts are divided into average e, sour and main.

There are also some other types of salts, for example: double salts, which contain two different cations and one anion: CaCO 3 × MgCO 3 (dolomite), KCl ∙ NaCl (sylvinite), KAl (SO 4 ) 2 (potassium alum); mixed salts, which contain one cation and two different anions: CaOCl 2 (or CaCl (OCl )) - calcium salt of hydrochloric and hypochlorous ( HOCl ) acids (calcium chloride-hypochlorite). Complex salts contain complex cations or anions: K 3 + [Fe (CN) 6] -3, K 4 + [Fe (CN) 6] -4, [Cr (H 2 O) 5 Cl] 2+ Cl 2 -.

According to modern nomenclature rules, the names of salts are formed from the name of the anion in the nominative case and the name of the cation in the genitive case. for example FeS - iron sulfide ( II), Fe 2 (SO 4 ) 3 - iron sulfate ( III ). The hydrogen atom, which is part of the acid salt, is denoted by the prefix hydro- ( NaHSO3 -sodium hydrosulfite), and the OH group - - prefix hydroxo- ( Al (OH) 2 Cl - aluminum dihydroxochloride).

Getting salts

Salts are closely related to all other classes of inorganic compounds and can be obtained from almost any class. Most of the methods for obtaining salts have already been discussed above (Sect. , ), these include:

1. Interaction of basic, acidic and amphoteric oxides with each other:

BaO + SiO 2 \u003d BaSiO 3,

MgO + Al 2 O 3 \u003d Mg (AlO 2) 2,

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

P 2 O 5 + Al 2 O 3 \u003d 2AlPO 4.

2. Interaction of oxides with hydroxides (with acids and bases):

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

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

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

3. Interaction of bases with medium and acid salts:

CuSO 4 + 2KOH \u003d Cu (OH) 2 ↓ + K 2 SO 4,

K 2 SO 4 + Ba(OH) 2 = 2KOH + BaSO 4↓ .

2NaHSO 3 + 2KOH \u003d Na 2 SO 3 + K 2 SO 3 + 2H 2 O,

Ca(HCO 3) 2 + Ba(OH) 2 = BaCO 3↓ + CaCO 3 ↓ + 2H 2 O.

Cu (OH) 2 + 2NaHSO 4 \u003d CuSO 4 + Na 2 SO 4 + 2H 2 O.

4. Salts of oxygen-free acids, in addition, can be obtained by direct interaction of metals and non-metals:

2 Mg + Cl 2 \u003d MgCl 2.

Chemical properties of salts

In the chemical reactions of salts, the features of both cations and anions that make up their composition are manifested. Metal cations in solutions can react with other anions to form insoluble compounds. On the other hand, anions that are part of salts can combine with cations to form precipitates or poorly dissociated compounds (or in redox reactions). Thus, salts can react:

1. With metals	Cu + HgCl 2 \u003d CuCl 2 + Hg, Zn + Pb (NO 3) 2 = Zn (NO 3) 2 + Pb.
2. With acids	Na 2 CO 3 + 2HCl \u003d 2NaCl + H 2 O + CO 2, AgCl + HBr = AgBr ↓ + HCl
3. With salts	AgNO 3 + NaCl \u003d AgCl ↓ + NaNO 3, K 2 CrO 4 + Pb (NO 3) 2 \u003d KNO 3 + PbCrO 4↓ .
4. With bases	CuSO 4 + 2NaOH \u003d Cu (OH) 2 ↓ + Na 2 SO 4, Ni (NO 3) 2 + 2KOH \u003d Ni (OH) 2 + 2KNO 3.
5. Many salts are stable when heated. However, ammonium salts, as well as some salts of low-active metals, weak acids and acids, in which elements exhibit higher or lower oxidation states, decompose when heated: CaCO 3 \u003d CaO + CO 2, 2Ag 2 CO 3 \u003d 4Ag + 2CO 2 + O 2, NH 4 Cl \u003d NH 3 + HCl, 2KNO 3 \u003d 2KNO 2 + O 2, 2FeSO 4 \u003d Fe 2 O 3 + SO 2 + SO 3, 4FeSO 4 \u003d 2Fe 2 O 3 + 4SO 2 + O 2, NH 4 NO 3 \u003d N 2 O + 2 H 2 O.

M.V. Andryukhova, L.N. Borodin

DEFINITION

salt- complex substances that dissociate in aqueous solutions into metal cations and anions of acid residues.

According to the IUPAC definition, salts are chemical compounds consisting of cations and anions.

Typical salts are crystalline substances with an ionic crystal lattice.

General formula of salts

General formula of salts: Kat n BUTm

As cations, the composition of salts can include metal cations, ammonium cations NH 4 +, phosphonium PH 4 +, their organic derivatives, various complex cations. The anions in salts are anions of acid residues of organic and inorganic acids, carbanions and complex anions.

Salt types

Salts can be thought of as the product of a neutralization reaction between the corresponding acid and base. Depending on the degree of substitution of protons or hydroxo groups,

• Medium (normal) salts- the product of complete replacement of cations in an acid molecule by cations.

• Acid salts- a product of partial replacement of hydrogen cations in an acid molecule by metal cations. Acid salts are formed when a base is neutralized with an excess of an acid (that is, under conditions of a lack of a base or an excess of an acid).

• Basic salts- a product of incomplete replacement of the hydroxyl groups of the base with acidic residues. Basic salts are formed under conditions of an excess of a base or a deficiency of an acid.

According to the number of cations and anions present in the salt structure,

• simple salts- salts consisting of one type of cations and one type of anions (CuSO 4);
• double salts- salts containing two different cations and one anion (KNaSO 4);
• mixed salts- salts containing two different anions and one cation (Ca(OCl)Cl).

If the salt contains molecules of crystallization water, then such salts are called hydrated or crystalline hydrates(Na 2 SO 4 10 H 2 O).

Complex salts contain a complex cation or complex anion (SO 4 , K 4 )