What salts are called average. Salts in chemistry: types and properties

Consider the most important ways to obtain salts.

Neutralization reaction . Acid and base solutions are mixed in the desired molar ratio. After evaporation of the water, a crystalline salt is obtained. For example:

2 . Reaction of acids with basic oxides . In fact, this is a variant of the neutralization reaction. For example:

3 . Reaction of bases with acidic oxides . This is also a variant of the neutralization reaction:

4 . The reaction of basic and acidic oxides with each other :

5 . Reaction of acids with salts . This method is suitable, for example, if an insoluble salt is formed that precipitates:

6 . Reaction of bases with salts . Only alkalis (soluble bases) are suitable for such reactions. These reactions produce another base and another salt. It is important that the new base is not alkaline and cannot react with the resulting salt. For example:

7. The reaction of two different salts. The reaction can be carried out only if at least one of the resulting salts is insoluble and precipitates:

The precipitated salt is filtered off and the remaining solution is evaporated to give another salt. If both formed salts are highly soluble in water, then the reaction does not occur: in the solution there are only ions that do not interact with each other:

NaCl + KBr = Na + + Cl - + K + + Br -

If such a solution is evaporated, then we get mixture salts NaCl, KBr, NaBr and KCl, but pure salts cannot be obtained in such reactions.

8 . Reaction of metals with acids . Salts are also formed in redox reactions. For example, metals located to the left of hydrogen in the metal activity series (Table 4-3) displace hydrogen from acids and combine with them themselves, forming salts:

9 . Reaction of metals with non-metals . This reaction outwardly resembles combustion. The metal "burns" in a non-metal current, forming tiny salt crystals that look like white "smoke":

10 . Reaction of metals with salts . More active metals in the activity series to the left, are able to displace less active (located to the right) metals from their salts:

Consider Chemical properties salts.

The most common salt reactions are exchange reactions and redox reactions. First, consider examples of redox reactions.

1 . Redox reactions of salts .

Since salts consist of metal ions and an acid residue, their redox reactions can be conditionally divided into two groups: reactions due to the metal ion and reactions due to the acid residue, if any atom in this acid residue is able to change the oxidation state.

AND) Reactions due to the metal ion.

Since salts contain a metal ion in a positive oxidation state, they can participate in redox reactions, where the metal ion plays the role of an oxidizing agent. The reducing agent is most often some other (more active) metal:

It is customary to say that more active metals are capable of displace other metals from their salts. Metals in the activity series to the left (see paragraph 8.3) are more active.

B) Reactions due to the acid residue.

Acid residues often contain atoms that can change the oxidation state. Hence, numerous redox reactions of salts with such acidic residues. For example:

2 . Exchange reactions of salts .

Such reactions can occur when salts react: a) with acids, b) with alkalis, c) with other salts. When carrying out exchange reactions, salt solutions are taken. The general requirement for such reactions is the formation of a sparingly soluble product, which is removed from the solution as a precipitate. For example:

a) CuSO 4 + H 2 S \u003d CuS ↓ (precipitate) + H 2 SO 4

AgNO 3 + HCl \u003d AgCl ↓ (precipitate) + HNO 3

b) FeCl 3 + 3 NaOH \u003d Fe (OH) 3 ↓ (precipitate) + 3 NaCl

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

c) BaCl 2 + K 2 SO 4 = BaSO 4 ↓ (precipitate) + 2 KCl

CaCl 2 + Na 2 CO 3 \u003d CaCO 3 ↓ (precipitate) + 2 NaCl

If at least one product of such exchange reactions does not leave the reaction sphere in the form of a precipitate (sometimes in the form of a gas), then when the solutions are mixed, only a mixture of ions is formed, into which the initial salt and reagent decompose upon dissolution. Thus, the exchange reaction cannot occur.

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 ANDm

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

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 - potassium tetrahydroxyaluminate, Na - sodium tetrahydroxychromate, K 4 - potassium hexacyanoferrate(H)).

Names of hydrated salts (crystalline hydrates) are formed in two ways. You can use the complex cation naming system described above; for example, copper sulfate SO 4 H 2 0 (or CuSO 4 5H 2 O) can be called tetraaquacopper(II) sulfate. However, for the most well-known hydrated salts, most often the number of water molecules (the degree of hydration) is indicated by a numerical prefix to the word "hydrate", for example: CuSO 4 5H 2 O - copper (I) sulfate pentahydrate, Na 2 SO 4 10H 2 O - sodium sulfate decahydrate, CaCl 2 2H 2 O - calcium chloride dihydrate.

Solubility of salts

According to their solubility in water, salts are divided into soluble (P), insoluble (H) and slightly soluble (M). To determine the solubility of salts, use the table of the solubility of acids, bases and salts in water. If there is no table at hand, then you can use the rules. They are easy to remember.

1. All salts of nitric acid are soluble - nitrates.

2. All salts of hydrochloric acid are soluble - chlorides, except for AgCl (H), PbCl 2 (M).

3. All salts of sulfuric acid - sulfates are soluble, except for BaSO 4 (H), PbSO 4 (H).

4. Sodium and potassium salts are soluble.

5. All phosphates, carbonates, silicates and sulfides do not dissolve, except for Na salts + and K + .

Of all chemical compounds, salts are the most numerous class of substances. These are solids, they differ from each other in color and solubility in water. At the beginning of the XIX century. Swedish chemist I. Berzelius formulated the definition of salts as reaction products of acids with bases or compounds obtained by replacing hydrogen atoms in an acid with a metal. On this basis, salts are distinguished as medium, acidic and basic. Medium, or normal, salts are products of the complete replacement of hydrogen atoms in an acid with a metal.

For example:

Na 2 CO 3 - sodium carbonate;

CuSO 4 - copper (II) sulfate, etc.

Such salts dissociate into metal cations and anions of the acid residue:

Na 2 CO 3 \u003d 2Na + + CO 2 -

Acid salts are products of incomplete replacement of hydrogen atoms in an acid by a metal. Acid salts include, for example, baking soda NaHCO 3 , which consists of a metal cation Na + and an acidic singly charged residue HCO 3 - . For an acidic calcium salt, the formula is written as follows: Ca (HCO 3) 2. The names of these salts are made up of the names of medium salts with the addition of the prefix hydro- , eg:

Mg (HSO 4) 2 - magnesium hydrosulfate.

Dissociate acid salts as follows:

NaHCO 3 \u003d Na + + HCO 3 -
Mg (HSO 4) 2 \u003d Mg 2+ + 2HSO 4 -

Basic salts are products of incomplete substitution of hydroxo groups in the base for an acid residue. For example, such salts include the famous malachite (CuOH) 2 CO 3, which you read about in the works of P. Bazhov. It consists of two basic cations CuOH + and a doubly charged anion of the acid residue CO 3 2- . The CuOH + cation has a +1 charge, therefore, in the molecule, two such cations and one doubly charged CO 3 2- anion are combined into an electrically neutral salt.

The names of such salts will be the same as for normal salts, but with the addition of the prefix hydroxo-, (CuOH) 2 CO 3 - copper (II) hydroxocarbonate or AlOHCl 2 - aluminum hydroxochloride. Most basic salts are insoluble or sparingly soluble.

The latter dissociate like this:

AlOHCl 2 \u003d AlOH 2 + + 2Cl -

Salt properties

The first two exchange reactions have been discussed in detail previously.

The third reaction is also an exchange reaction. It flows between salt solutions and is accompanied by the formation of a precipitate, for example:

The fourth reaction of salts is associated with the position of the metal in the electrochemical series of metal voltages (see "Electrochemical series of metal voltages"). Each metal displaces from salt solutions all other metals located to the right of it in a series of voltages. This is subject to the following conditions:

1) both salts (both reacting and formed as a result of the reaction) must be soluble;

2) metals should not interact with water, therefore, metals of the main subgroups of groups I and II (for the latter, starting with Ca) do not displace other metals from salt solutions.

Methods for obtaining salts

Methods for obtaining and chemical properties of salts. Salts can be obtained from inorganic compounds of almost any class. Along with these methods, salts of anoxic acids can be obtained by direct interaction of a metal and a non-metal (Cl, S, etc.).

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

2Cu(NO 3) 2 \u003d 2CuO + 4NO 2 + O 2

2AgNO 3 \u003d 2Ag + 2NO 2 + O 2

NH 4 NO 3 \u003d N 2 O + 2H 2 O

(NH 4) 2 Cr 2 O 7 \u003d Cr 2 O 3 + N 2 + 4H 2 O

2KSlO 3 \u003d MnO 2 \u003d 2KCl + 3O 2

4KClO 3 \u003d 3KSlO 4 + KCl

Salts are complex substances that are the product of complete or incomplete replacement of hydrogen atoms of an acid with metal atoms, or replacement of hydroxo groups of a base with an acid residue.

Depending on the composition, salts are divided into medium (Na2SO4, K3PO4), acidic (NaHCO3, MgHPO4), basic (FeOHCl2, Al(OH)2Cl, (CaOH)2CO3, double (KAl(SO4)2), complex (Ag[( NH3)2]Cl, K4).

Medium salts

Average salts are called salts, which are the product of the complete replacement of hydrogen atoms of the corresponding acid with metal atoms or an NH4 + ion. For example:

H2CO3 ® (NH4)2CO3; H3PO4 ® Na3PO4

The name of the middle salt is formed from the name of the anion followed by the name of the cation. For salts of oxygen-free acids, the name of the salt is made up of the Latin name of the non-metal with the addition of the suffix –id For example, NaCl is sodium chloride. If a non-metal exhibits a variable degree of oxidation, then after its name, the degree of oxidation of the metal is indicated in brackets in Roman numerals: FeS - iron (II) sulfide, Fe2S3 - iron (III) sulfide.

For salts of oxygen-containing acids, the ending is added to the Latin root of the name of the element -at for higher oxidation states, -it for the lower ones. For example,

K2SiO3 is potassium silicate, KNO2 is potassium nitrite,

KNO3 - potassium nitrate, K3PO4 - potassium phosphate,

Fe2(SO4)3 is iron (III) sulfate, Na2SO3 is sodium sulfite.

For salts of some acids, the prefix is ​​used -hypo for lower oxidation states and –per for high oxidation states. For example,

KClO - potassium hypochlorite, KClO2 - potassium chlorite,

KClO3 is potassium chlorate, KClO4 is potassium perchlorate.

Methods for obtaining medium salts:

The interaction of metals with non-metals, acids and salts:

2Na + Cl2 = 2NaCl

Zn + 2HCl = ZnCl2 + H2

Fe + CuSO4 = FeSO4 + Cu

The interaction of oxides:

basic with acids BaO + 2HNO3 = Ba(NO3)2 + H2O

acidic with alkalis 2NaOH + SiO2 = Na2SiO3 + H2O

basic oxides with acidic Na2O + CO2 = Na2CO3

The interaction of acids with bases and with amphoteric hydroxides:

KOH + HCl = KCl + H2O

Cr(OH)3 + 3HNO3 = Cr(NO3)3 + 3H2O

The interaction of salts with acids, with alkalis and salts:

Na2CO3 + 2HCl = 2NaCl + CO2 + H2O

FeCl3 + 3KOH = 3KCl + Fe(OH)3¯

Na2SO4 + BaCl2 = BaSO4¯ + 2NaCl

Chemical properties of medium salts:

Interaction with metals

Zn + Hg(NO3)2 = Zn(NO3)2 + Hg

Interaction with acids

AgNO3 + HCl = AgCl¯ + HNO3

Interaction with alkalis

CuSO4 + 2NaOH = Cu(OH)2¯ + Na2SO4

Salt interaction

CaCl2 + Na2CO3 = CaCO3¯ + 2NaCl

Salt decomposition

NH4Cl = NH3 + HCl

CaCO3 = CaO + CO2

(NH4)2Cr2O7 = N2 + Cr2O3 + 4H2O

Acid salts

Acid salts are products of incomplete replacement of hydrogen atoms in molecules of polybasic acids by metal atoms.

For example: H2CO3 ® NaHCO3

H3PO4 ® NaH2PO4 ® Na2HPO4

When naming an acid salt, the prefix is ​​added to the name of the corresponding medium salt hydro-, which indicates the presence of hydrogen atoms in the acid residue.

For example, NaHS is sodium hydrosulfide, Na2HPO4 is sodium hydrogen phosphate, NaH2PO4 is sodium dihydrogen phosphate.

Acid salts can be obtained:

The action of an excess of polybasic acids on basic oxides, alkalis and medium salts:

K2O + 2H2S = 2KHS + H2O

NaOH + H2SO4 = NaHSO4 + H2O

K2SO4 + H2SO4 = 2KHSO4

The action of an excess of acidic oxides on alkalis

NaOH + CO2 = NaHCO3

Chemical properties of acid salts:

Interaction with excess alkali

Ca(HCO3)2 + Ca(OH)2 = 2CaCO3 + 2H2O

Interaction with acids

Ca(HCO3)2 + 2HCl = CaCl2 + 2H2O + 2CO2

Decomposition

Ca(HCO3)2 = CaCO3 + CO2 + H2O

Basic salts

Basic salts are products of incomplete substitution of the hydroxo group in the molecules of polyacid bases for acidic residues.

Mg(OH)2 ® MgOHNO3

Fe(OH)3 ®Fe(OH)2Cl ® FeOHCl2

When naming the basic salt, the prefix is ​​added to the name of the corresponding medium salt hydroxo-, which indicates the presence of a hydroxo group. For example, CrOHCl2 is chromium (III) hydroxochloride, Cr(OH)2Cl is chromium (III) dihydroxochloride.

Basic salts can be obtained:

Incomplete neutralization of bases by acids

Bases can interact:

• with non-metals

  6KOH + 3S → K2SO 3 + 2K 2 S + 3H 2 O;

• with acidic oxides -

  2NaOH + CO 2 → Na 2 CO 3 + H 2 O;

• with salts (precipitation, gas release) -

  2KOH + FeCl 2 → Fe(OH) 2 + 2KCl.

There are also other ways to get:

• the interaction of two salts -

  CuCl 2 + Na 2 S → 2NaCl + CuS↓;

• reaction of metals and non-metals -
• combination of acidic and basic oxides -

  SO 3 + Na 2 O → Na 2 SO 4;

• interaction of salts with metals -

  Fe + CuSO 4 → FeSO 4 + Cu.

Chemical properties

Soluble salts are electrolytes and are subject to dissociation reactions. When interacting with water, they disintegrate, i.e. dissociate into positively and negatively charged ions - cations and anions, respectively. Metal ions are cations, acid residues are anions. Examples of ionic equations:

• NaCl → Na + + Cl - ;
• Al 2 (SO 4) 3 → 2Al 3 + + 3SO 4 2− ;
• CaClBr → Ca2 + + Cl - + Br - .

In addition to metal cations, ammonium (NH4 +) and phosphonium (PH4 +) cations may be present in salts.

Other reactions are described in the table of chemical properties of salts.

Rice. 3. Isolation of sediment upon interaction with bases.

Some salts, depending on the type, decompose when heated into a metal oxide and an acid residue or into simple substances. For example, CaCO 3 → CaO + CO 2, 2AgCl → Ag + Cl 2.

What have we learned?

From the 8th grade chemistry lesson, we learned about the features and types of salts. Complex inorganic compounds consist of metals and acid residues. May include hydrogen (acid salts), two metals, or two acid residues. These are solid crystalline substances that are formed as a result of the reactions of acids or alkalis with metals. React with bases, acids, metals, other salts.

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