What are acid salts in chemistry. Properties of salts: physical and chemical. Salt production

1. Salts are electrolytes.

In aqueous solutions, salts dissociate into positively charged metal ions (cations) and negatively charged ions (anions) of acid residues.

for example, when sodium chloride crystals are dissolved in water, positively charged sodium ions and negatively charged chloride ions, from which the crystal lattice of this substance is formed, go into solution:

NaCl → NaCl - .

During the electrolytic dissociation of aluminum sulfate, positively charged aluminum ions and negatively charged sulfate ions are formed:

Al 2 SO 4 3 → 2 Al 3 3 SO 4 2 - .

2. Salts can interact with metals.

During the substitution reaction taking place in aqueous solution, a more reactive metal displaces a less reactive one.

for example, if a piece of iron is placed in a solution of copper sulfate, it is covered with a red-brown precipitate of copper. The solution gradually changes color from blue to pale green as an iron salt is formed (\ (II \)):

Fe Cu SO 4 → Fe SO 4 Cu ↓ .

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When copper chloride (\ (II \)) reacts with aluminum, aluminum chloride and copper are formed:
2 Al 3Cu Cl 2 → 2Al Cl 3 3 Cu ↓ .

3. Salts can interact with acids.

An exchange reaction occurs, during which a chemically more active acid displaces a less active one.

for example, when a solution of barium chloride reacts with sulfuric acid, a precipitate of barium sulfate is formed, and hydrochloric acid remains in the solution:
BaCl 2 H 2 SO 4 → Ba SO 4 ↓ 2 HCl.

When calcium carbonate reacts with hydrochloric acid calcium chloride and carbonic acid are formed, which immediately decomposes into carbon dioxide and water:

CaCO 3 2 HCl → CaCl 2 H 2 O CO 2 H 2 CO 3 .

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4. Water-soluble salts can interact with alkalis.

An exchange reaction is possible if, as a result, at least one of the products is practically insoluble (precipitates).

for example, when nickel nitrate (\ (II \)) reacts with sodium hydroxide, sodium nitrate and practically insoluble nickel hydroxide (\ (II \)) are formed:
Ni NO 3 2 2 NaOH → Ni OH 2 ↓ 2Na NO 3.

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When sodium carbonate (soda) reacts with calcium hydroxide (slaked lime), sodium hydroxide and practically insoluble calcium carbonate are formed:
Na 2 CO 3 CaOH 2 → 2NaOH CaCO 3 ↓.

5. Water-soluble salts can enter into an exchange reaction with other water-soluble salts if at least one practically insoluble substance is formed as a result.

for example, when sodium sulfide reacts with silver nitrate, sodium nitrate and practically insoluble silver sulfide are formed:
Na 2 S 2Ag NO 3 → Na NO 3 Ag 2 S ↓.

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When barium nitrate reacts with potassium sulfate, potassium nitrate and practically insoluble barium sulfate are formed:
Ba NO 3 2 K 2 SO 4 → 2 KNO 3 BaSO 4 ↓ .

6. Some salts decompose when heated.

Moreover, the chemical reactions that occur in this case can be divided into two groups:

• reactions in which elements do not change their oxidation state
• redox reactions.

A. Salt decomposition reactions that occur without changing the oxidation state of elements.

As examples of such chemical reactions Let us consider how the decomposition of carbonates proceeds.

When heated strongly, calcium carbonate (chalk, limestone, marble) decomposes, forming calcium oxide (burnt lime) and carbon dioxide:
CaCO 3 t ° CaO CO 2 .

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Sodium bicarbonate (baking soda) with slight heating decomposes into sodium carbonate (soda), water and carbon dioxide:
2 NaHCO 3 t ° Na 2 CO 3 H 2 O CO 2 .

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Crystal hydrates of salts lose water when heated. For example, copper sulfate pentahydrate (\ (II \)) (copper sulfate), gradually losing water, turns into anhydrous copper sulfate (\ (II \)):
CuSO 4 ⋅ 5 H 2 O → t ° CuSO 4 5 H 2 O.

Under normal conditions, the anhydrous copper sulfate formed can be converted into a crystalline hydrate:
CuSO 4 5 H 2 O → CuSO 4 ⋅ 5 H 2 O

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Salts - organic and inorganic chemical substances complex composition. In chemical theory there is no strict and definitive definition of salts. They can be described as compounds:
- consisting of anions and cations;
- obtained as a result of the interaction of acids and bases;
- consisting of acidic residues and metal ions.

Acid residues can be associated not with metal atoms, but with ammonium ions (NH 4) +, phosphonium (PH 4) +, hydroxonium (H 3 O) + and some others.

Salt types

Acid, medium, basic. If in an acid all hydrogen protons are replaced by metal ions, then such salts are called medium salts, for example, NaCl. If hydrogen is only partially substituted, then such salts are acidic, for example. KHSO 4 and NaH 2 PO 4 . If a hydroxyl groups(OH) - the bases are not completely replaced by the acid residue, then the salt is basic, for example. CuCl(OH), Al(OH)SO 4 .

- Single, double, mixed. Simple salts consist of one metal and one acid residue, such as K 2 SO 4 . There are two metals in double salts, for example KAl(SO 4) 2 . In mixed salts, two acid residues, for example. AgClBr.

Organic and inorganic.
- Complex salts with a complex ion: K 2 , Cl 2 and others.
- Crystal hydrates and crystal solvates.
- Crystalline hydrates with molecules of water of crystallization. CaSO 4 * 2H 2 O.
- Crystalsolvates with solvent molecules. For example, LiCl in liquid ammonia NH 3 gives LiCl*5NH 3 solvate.
- Oxygen-containing and oxygen-free.
- Internal, otherwise called bipolar ions.

Properties

Most salts are solids with a high melting point and do not conduct electricity. Solubility in water is an important characteristic; on its basis, reagents are divided into water-soluble, slightly soluble and insoluble. Many salts are soluble in organic solvents.

Salts react:
- with more active metals;
- with acids, bases, other salts, if during the interaction substances are obtained that do not participate in the further reaction, for example, gas, insoluble precipitate, water. Decompose when heated, hydrolyze in water.

In nature, salts are widely distributed in the form of minerals, brines, salt deposits. They are also obtained from sea ​​water, mountain ores.

Salts are essential for the human body. Iron salts are needed to replenish hemoglobin, calcium - are involved in the formation of the skeleton, magnesium - regulate the activity of the gastrointestinal tract.

The use of salts

Salts are actively used in production, everyday life, agriculture, medicine, food industry, chemical synthesis and analysis, in laboratory practice. Here are just a few of their areas of application:

- Sodium, potassium, calcium and ammonium nitrates (saltpeter); calcium phosphate, potassium chloride - raw material for the production of fertilizers.
- Sodium chloride is necessary for obtaining food table salt, used in the chemical industry for the production of chlorine, soda, caustic soda.
- Sodium hypochlorite is a popular bleach and water disinfectant.
- Salts of acetic acid (acetates) are used in the food industry as preservatives (potassium and calcium acetate); in medicine for the manufacture of medicines, in the cosmetic industry (sodium acetate), for many other purposes.
- Potassium alum and potassium chromium alum are in demand in medicine, food industry; for dyeing fabrics, leather, furs.
- Many salts are used as fixants to determine chemical composition substances, water quality, acidity level, etc.

Our store offers a wide range of salts, both organic and inorganic.

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 located in the activity row 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.

BUT) 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.

In order to answer the question of what salt is, you usually don’t have to think for a long time. This is chemical compound in Everyday life occurs quite frequently. There is no need to talk about ordinary table salt. Detailed internal structure salts and their compounds are studied by inorganic chemistry.

Salt definition

A clear answer to the question of what salt is can be found in the works of M. V. Lomonosov. He gave this name to fragile bodies that can dissolve in water and do not ignite under the influence of high temperatures or open fire. Later, the definition was derived not from their physical, but from the chemical properties of these substances.

An example of a mixed one is the calcium salt of hydrochloric and hypochlorous acid: CaOCl 2.

Nomenclature

Salts formed by metals with variable valency have an additional designation: after the formula, the valency is written in brackets in Roman numerals. So, there is iron sulfate FeSO 4 (II) and Fe 2 (SO4) 3 (III). In the name of salts there is a prefix hydro-, if there are unsubstituted hydrogen atoms in its composition. For example, potassium hydrogen phosphate has the formula K 2 HPO 4 .

Properties of salts in electrolytes

The theory of electrolytic dissociation gives its own interpretation chemical properties. In the light of this theory, a salt can be defined as a weak electrolyte that, when dissolved, dissociates (breaks down) in water. Thus, a salt solution can be represented as a complex of positive negative ions, and the first ones are not H + hydrogen atoms, and the second ones are not OH - hydroxo group atoms. There are no ions that would be present in all types of salt solutions, so any common properties they don't possess. The lower the charges of the ions that form the salt solution, the better they dissociate, the better the electrical conductivity of such a liquid mixture.

Acid salt solutions

Acid salts in solution decompose into complex negative ions, which are an acid residue, and simple anions, which are positively charged metal particles.

For example, the dissolution reaction of sodium bicarbonate leads to the decomposition of the salt into sodium ions and the rest of HCO 3 -.

Full formula looks like this: NaHCO 3 = Na + + HCO 3 -, HCO 3 - = H + + CO 3 2-.

Solutions of basic salts

The dissociation of basic salts leads to the formation of acid anions and complex cations consisting of metals and hydroxogroups. These complex cations, in turn, are also able to decompose in the process of dissociation. Therefore, in any solution of a salt of the main group, there are OH - ions. For example, the dissociation of hydroxomagnesium chloride proceeds as follows:

Distribution of salts

What is salt? This element is one of the most common chemical compounds. Everyone knows table salt, chalk (calcium carbonate) and so on. Among the carbonate salts, the most common is calcium carbonate. He is integral part marble, limestone, dolomite. And calcium carbonate is the basis for the formation of pearls and corals. This chemical compound is essential for the formation of hard integuments in insects and skeletons in chordates.

Salt has been known to us since childhood. Doctors warn against its excessive use, but in moderation it is essential for the implementation of vital processes in the body. And it is needed to maintain the correct composition of the blood and the production of gastric juice. Saline solutions, an integral part of injections and droppers, are nothing more than a solution of table salt.

In the previous sections, reactions in which salts are formed were constantly encountered.

Salts are substances in which metal atoms are bonded to acidic residues.

The exception is ammonium salts, in which not metal atoms are bound to acidic residues, but NH 4 + particles. Examples of typical salts are given below.

NaCl - sodium chloride,

Na 2 SO 4 - sodium sulfate,

CaSO 4 - calcium sulfate,

CaCl 2 - calcium chloride,

(NH 4) 2 SO 4 - ammonium sulfate.

The salt formula is built taking into account the valencies of the metal and the acid residue. Almost all salts are ionic compounds, so we can say that metal ions and ions of acid residues are interconnected in salts:

Na + Cl - - sodium chloride

Ca 2+ SO 4 2– - calcium sulfate, etc.

The names of salts are made up of the name of the acid residue and the name of the metal. The main thing in the name is the acid residue. The names of salts depending on the acid residue are shown in Table 4.6. At the top of the table, oxygen-containing acid residues are given, and at the bottom, oxygen-free ones.

Table 4-6. Construction of names of salts.

Table 4-6 shows that the names of oxygen-containing salts have the endings " at", and the names of oxygen-free salts - the endings" id».

In some cases, the ending " it". For example, Na 2 SO 3 - sulfite sodium. This is done in order to distinguish between salts of sulfuric acid (H 2 SO 4) and sulfurous acid (H 2 SO 3) and in other similar cases.

All salts are divided into medium, sour and main. Medium salts contain only metal and acid residue atoms. For example, all salts from Table 4-6 are average salts.

Any salt can be obtained by an appropriate neutralization reaction. For example, sodium sulfite is formed in the reaction between sulfurous acid and a base (caustic soda). In this case, for 1 mole of acid, you need to take 2 moles of base:

If you take only 1 mole of base - that is, less than is required for complete neutralization, then sour salt - sodium hydrosulfite:

Sour salts are formed by polybasic acids. Monobasic acids do not form acid salts.

Acid salts, in addition to metal ions and acid residue, contain hydrogen ions.

The names of acid salts contain the prefix "hydro" (from the word hydrogenium - hydrogen). For example:

NaHCO 3 - sodium bicarbonate,

K 2 HPO 4 - potassium hydrogen phosphate,

KH 2 PO 4 - potassium dihydrogen phosphate.

Main salts are formed when the base is not completely neutralized. The names of the basic salts are formed using the prefix "hydroxo". Below is an example showing the difference between basic salts and ordinary (medium) salts:

Basic salts, in addition to metal ions and acid residue, contain hydroxyl groups.

Basic salts are formed only from polyacid bases. Single acid bases cannot form such salts.

Table 4.6 shows international titles salts. However, it is also useful to know the Russian names and some historically established, traditional names of salts that are important (table 4.7).

Table 4.7. International, Russian and traditional names of some important salts.

For example, in no case should one confuse soda Na 2 CO 3 and drinking soda NaHC03. If accidentally eaten soda instead of drinking soda, you can get a severe chemical burn.

In chemistry and technology, many ancient names are still preserved. For example, caustic soda- not a salt at all, but the technical name of sodium hydroxide NaOH. If you can clean the sink or dishes with ordinary soda, then under no circumstances should you pick up caustic soda or use it in everyday life!

The structure of salts is similar to the structure of the corresponding acids and bases. Below are the structural formulas of typical medium, acid and basic salts.

Let us give the structure and name of the basic salt, the formula of which looks like: 2 CO 3 - iron (III) dihydroxocarbonate. When considering the structural formula of such a salt, it becomes clear that this salt is a product of the partial neutralization of iron (III) hydroxide with carbonic acid: