How to distinguish strong electrolytes from weak ones? and got the best answer

Answer from Pavel Beskrovny[master]
STRONG ELECTROLYTES, when dissolved in water, almost completely dissociate into ions. For such electrolytes, the VALUE OF THE DEGREE OF DISSOCIATION tends to UNITY in dilute solutions.
Strong electrolytes include:
1) almost all salts;
2) strong acids, for example: H2SO4 (sulfuric acid), HCl (hydrochloric acid), HNO3 (nitric acid);
3) all alkalis, for example: NaOH (sodium hydroxide), KOH (potassium hydroxide).
WEAK ELECTROLYTES, when dissolved in water, almost do not dissociate into ions. For such electrolytes, the VALUE OF THE DEGREE OF DISSOCIATION tends to ZERO.
Weak electrolytes include:
1) weak acids - H2S (hydrogen sulfide), H2CO3 (carbonic acid), HNO2;
2) aqueous solution of ammonia NH3 * H2O
DEGREE OF DISSOCIATION is the ratio of the number of particles disintegrated into ions (Nd) to the total number of dissolved particles (Np) (denoted by the Greek letter alpha):
a= Nd / Nr. Electrolytic dissociation is a reversible process for weak electrolytes. I hope you know what electrolytes are, since you’re asking. This is simpler, if it’s more complicated, then see above (for a number of EOs).
Electrolytic dissociation is a reversible process for weak electrolytes.
If you have questions, then go to soap.

Strong electrolytes, when dissolved in water, almost completely dissociate into ions, regardless of their concentration in the solution.

Therefore, in the dissociation equations of strong electrolytes, an equal sign (=) is used.

Strong electrolytes include:

Soluble salts;

Many inorganic acids: HNO3, H2SO4, HCl, HBr, HI;

Bases formed by alkali metals (LiOH, NaOH, KOH, etc.) and alkaline earth metals (Ca(OH)2, Sr(OH)2, Ba(OH)2).

Weak electrolytes in aqueous solutions only partially (reversibly) dissociate into ions.

Therefore, in the dissociation equations of weak electrolytes, the reversibility sign (⇄) is used.

Weak electrolytes include:

Almost all organic acids and water;

Some inorganic acids: H2S, H3PO4, H2CO3, HNO2, H2SiO3, etc.;

Insoluble metal hydroxides: Mg(OH)2, Fe(OH)2, Zn(OH)2, etc.

Ionic reaction equations

Ionic reaction equations
Chemical reactions in solutions of electrolytes (acids, bases and salts) occur with the participation of ions. The final solution may remain clear (the products are highly soluble in water), but one of the products will be a weak electrolyte; in other cases, precipitation or gas evolution will occur.

For reactions in solutions involving ions, not only the molecular equation is compiled, but also the full ionic equation and the short ionic equation.
In ionic equations, according to the proposal of the French chemist K. -L. According to Berthollet (1801), all strong, readily soluble electrolytes are written in the form of ion formulas, and sediments, gases and weak electrolytes are written in the form of molecular formulas. The formation of precipitation is marked with a “down arrow” (↓), the formation of gases with an “up arrow” (). An example of writing a reaction equation using Berthollet’s rule:

a) molecular equation
Na2CO3 + H2SO4 = Na2SO4 + CO2 + H2O
b) complete ionic equation
2Na+ + CO32− + 2H+ + SO42− = 2Na+ + SO42− + CO2 + H2O
(CO2 - gas, H2O - weak electrolyte)
c) brief ionic equation
CO32− + 2H+ = CO2 + H2O

Usually, when writing, they are limited to a brief ionic equation, with solid reagents denoted by the index (t), gaseous reagents by the index (g). Examples:

1) Cu(OH)2(t) + 2HNO3 = Cu(NO3)2 + 2H2O
Cu(OH)2(t) + 2H+ = Cu2+ + 2H2O
Cu(OH)2 is practically insoluble in water
2) BaS + H2SO4 = BaSO4↓ + H2S
Ba2+ + S2− + 2H+ + SO42− = BaSO4↓ + H2S
(the full and short ionic equations are the same)
3) CaCO3(t) + CO2(g) + H2O = Ca(HCO3)2
CaCO3(s) + CO2(g) + H2O = Ca2+ + 2HCO3−
(most acid salts are highly soluble in water).

If strong electrolytes are not involved in the reaction, the ionic form of the equation is absent:

Mg(OH)2(s) + 2HF(r) = MgF2↓ + 2H2O

TICKET No. 23

Hydrolysis of salts

Salt hydrolysis is the interaction of salt ions with water to form slightly dissociating particles.

Hydrolysis, literally, is decomposition by water. By defining the reaction of salt hydrolysis in this way, we emphasize that salts in solution are in the form of ions, and that the driving force of the reaction is the formation of slightly dissociating particles (a general rule for many reactions in solutions).

Hydrolysis occurs only in those cases when the ions formed as a result of the electrolytic dissociation of the salt - a cation, an anion, or both together - are capable of forming weakly dissociating compounds with water ions, and this, in turn, occurs when the cation is strongly polarizing ( cation of a weak base), and the anion is easily polarized (anion of a weak acid). This changes the pH of the environment. If the cation forms a strong base, and the anion forms a strong acid, then they do not undergo hydrolysis.

1. Hydrolysis of a salt of a weak base and a strong acid passes through the cation, a weak base or basic salt may be formed and the pH of the solution will decrease

2. Hydrolysis of a salt of a weak acid and a strong base passes through the anion, a weak acid or acid salt may be formed and the pH of the solution will increase

3. Hydrolysis of a salt of a weak base and a weak acid usually passes completely to form a weak acid and a weak base; The pH of the solution differs slightly from 7 and is determined by the relative strength of the acid and base

4. Hydrolysis of a salt of a strong base and a strong acid does not occur

Question 24 Classification of oxides

Oxides are called complex substances whose molecules include oxygen atoms in oxidation state - 2 and some other element.

Oxides can be obtained through the direct interaction of oxygen with another element, or indirectly (for example, during the decomposition of salts, bases, acids). Under normal conditions, oxides come in solid, liquid and gaseous states; this type of compound is very common in nature. Oxides are found in the Earth's crust. Rust, sand, water, carbon dioxide are oxides.

Salt-forming oxides For example,

CuO + 2HCl → CuCl 2 + H 2 O.

CuO + SO 3 → CuSO 4.

Salt-forming oxides- These are oxides that form salts as a result of chemical reactions. These are oxides of metals and non-metals, which, when interacting with water, form the corresponding acids, and when interacting with bases, the corresponding acidic and normal salts. For example, Copper oxide (CuO) is a salt-forming oxide, because, for example, when it reacts with hydrochloric acid (HCl), a salt is formed:

CuO + 2HCl → CuCl 2 + H 2 O.

As a result of chemical reactions, other salts can be obtained:

CuO + SO 3 → CuSO 4.

Non-salt-forming oxides These are oxides that do not form salts. Examples include CO, N 2 O, NO.

1. ELECTROLYTES

1.1. Electrolytic dissociation. Degree of dissociation. Electrolyte Power

According to the theory of electrolytic dissociation, salts, acids, and hydroxides, when dissolved in water, completely or partially disintegrate into independent particles - ions.

The process of decomposition of substance molecules into ions under the influence of polar solvent molecules is called electrolytic dissociation. Substances that dissociate into ions in solutions are called electrolytes. As a result, the solution acquires the ability to conduct electric current, because mobile electric charge carriers appear in it. According to this theory, when dissolved in water, electrolytes break up (dissociate) into positively and negatively charged ions. Positively charged ions are called cations; these include, for example, hydrogen and metal ions. Negatively charged ions are called anions; These include ions of acidic residues and hydroxide ions.

To quantitatively characterize the dissociation process, the concept of the degree of dissociation was introduced. The degree of dissociation of an electrolyte (α) is the ratio of the number of its molecules disintegrated into ions in a given solution ( n ), to the total number of its molecules in solution ( N), or

α = .

The degree of electrolytic dissociation is usually expressed either in fractions of a unit or as a percentage.

Electrolytes with a degree of dissociation greater than 0.3 (30%) are usually called strong, with a degree of dissociation from 0.03 (3%) to 0.3 (30%) - medium, less than 0.03 (3%) - weak electrolytes. So, for a 0.1 M solution CH3COOH α = 0.013 (or 1.3%). Therefore, acetic acid is a weak electrolyte. The degree of dissociation shows what part of the dissolved molecules of a substance has broken up into ions. The degree of electrolytic dissociation of an electrolyte in aqueous solutions depends on the nature of the electrolyte, its concentration and temperature.

By their nature, electrolytes can be divided into two large groups: strong and weak. Strong electrolytes dissociate almost completely (α = 1).

Strong electrolytes include:

1) acids (H 2 SO 4, HCl, HNO 3, HBr, HI, HClO 4, H M nO 4);

2) bases – metal hydroxides of the first group of the main subgroup (alkali) – LiOH, NaOH, KOH, RbOH, CsOH , as well as hydroxides of alkaline earth metals – Ba (OH) 2, Ca (OH) 2, Sr (OH) 2;.

3) salts soluble in water (see solubility table).

Weak electrolytes dissociate into ions to a very small extent; in solutions they are found mainly in an undissociated state (in molecular form). For weak electrolytes, an equilibrium is established between undissociated molecules and ions.

Weak electrolytes include:

1) inorganic acids ( H 2 CO 3, H 2 S, HNO 2, H 2 SO 3, HCN, H 3 PO 4, H 2 SiO 3, HCNS, HClO, etc.);

2) water (H 2 O);

3) ammonium hydroxide ( NH 4 OH);

4) most organic acids

(for example, acetic CH 3 COOH, formic HCOOH);

5) insoluble and slightly soluble salts and hydroxides of some metals (see solubility table).

Process electrolytic dissociation depicted using chemical equations. For example, dissociation of hydrochloric acid (HC l ) is written as follows:

HCl → H + + Cl – .

Bases dissociate to form metal cations and hydroxide ions. For example, the dissociation of KOH

KOH → K + + OH – .

Polybasic acids, as well as bases of polyvalent metals, dissociate stepwise. For example,

H 2 CO 3 H + + HCO 3 – ,

HCO 3 – H + + CO 3 2– .

The first equilibrium - dissociation according to the first step - is characterized by the constant

.

For second stage dissociation:

.

In the case of carbonic acid, the dissociation constants have the following values: K I = 4.3× 10 –7, K II = 5.6 × 10–11. For stepwise dissociation always K I > K II > K III >... , because the energy that must be expended to separate an ion is minimal when it is separated from a neutral molecule.

Average (normal) salts, soluble in water, dissociate to form positively charged metal ions and negatively charged ions of the acid residue

Ca(NO 3) 2 → Ca 2+ + 2NO 3 –

Al 2 (SO 4) 3 → 2Al 3+ +3SO 4 2–.

Acid salts (hydrosalts) are electrolytes containing hydrogen in the anion, which can be split off in the form of the hydrogen ion H +. Acid salts are considered as a product obtained from polybasic acids in which not all hydrogen atoms are replaced by a metal. Dissociation of acid salts occurs in stages, for example:

KHCO 3 → K + + HCO 3 – (first stage)

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§ 6.3. Strong and weak electrolytes

The material in this section is partially familiar to you from previously studied school chemistry courses and from the previous section. Let's briefly review what you know and get acquainted with new material.

In the previous section, we discussed the behavior in aqueous solutions of some salts and organic substances that completely decompose into ions in an aqueous solution.
There is a number of simple but undeniable evidence that some substances in aqueous solutions disintegrate into particles. Thus, aqueous solutions of sulfuric H2SO4, nitric HNO3, chloric HClO4, hydrochloric (hydrochloric) HCl, acetic CH3COOH and other acids have a sour taste. In the formulas of acids, the common particle is the hydrogen atom, and it can be assumed that it (in the form of an ion) is the reason for the same taste of all these so different substances.
Hydrogen ions formed during dissociation in an aqueous solution give the solution a sour taste, which is why such substances are called acids. In nature, only hydrogen ions have a sour taste. They create a so-called acidic (sour) environment in an aqueous solution.

Remember, when you say “hydrogen chloride”, you mean the gaseous and crystalline state of this substance, but for an aqueous solution you should say “hydrogen chloride solution”, “hydrochloric acid” or use the common name “hydrochloric acid”, although the composition of the substance in any state expressed by the same formula - HCl.

Aqueous solutions of lithium (LiOH), sodium (NaOH), potassium (KOH), barium (Ba(OH)2), calcium (Ca(OH)2) and other metal hydroxides have the same unpleasant bitter-soapy taste and cause feeling of sliding. Apparently, the OH – hydroxide ions included in such compounds are responsible for this property.
Hydrochloric acid HCl, hydrobromic HBr and hydroiodic acid HI react with zinc in the same way, despite their different composition, since in reality it is not the acid that reacts with zinc:

Zn + 2HCl = ZnСl 2 + H2,

and hydrogen ions:

Zn + 2H + = Zn 2+ + H 2,

and hydrogen gas and zinc ions are formed.
Mixing some salt solutions, for example, potassium chloride KCl and sodium nitrate NaNO 3, is not accompanied by a noticeable thermal effect, although after evaporation of the solution a mixture of crystals of four substances is formed: the original ones - potassium chloride and sodium nitrate - and new ones - potassium nitrate KNO 3 and sodium chloride NaCl . It can be assumed that in the solution the two initial salts completely disintegrate into ions, which, when evaporated, form four crystalline substances:

Comparing this information with the electrical conductivity of aqueous solutions of acids, hydroxides and salts and with a number of other provisions, S.A. Arrhenius in 1887 put forward the hypothesis of electrolytic dissociation, according to which molecules of acids, hydroxides and salts, when dissolved in water, dissociate into ions.
The study of electrolysis products allows one to assign positive or negative charges to ions. Obviously, if an acid, for example nitric HNO 3, dissociates, say, into two ions and during electrolysis of an aqueous solution hydrogen is released at the cathode (negatively charged electrode), then, consequently, there are positively charged hydrogen ions H + in the solution. Then the dissociation equation should be written as follows:

НNO 3 = Н + + .

Electrolytic dissociation– complete or partial disintegration of a compound when dissolved in water into ions as a result of interaction with a molecule of water (or other solvent).
Electrolytes– acids, bases or salts, aqueous solutions of which conduct electric current as a result of dissociation.
Substances that do not dissociate into ions in an aqueous solution and whose solutions do not conduct electric current are called non-electrolytes.
The dissociation of electrolytes is quantitatively characterized degree of dissociation– the ratio of the number of “molecules” (formula units) disintegrated into ions to the total number of “molecules” of the dissolved substance. The degree of dissociation is indicated by the Greek letter. For example, if out of every 100 “molecules” of a dissolved substance, 80 dissociate into ions, then the degree of dissociation of the dissolved substance is equal to: = 80/100 = 0.8, or 80%.
According to their ability to dissociate (or, as they say, “by strength”), electrolytes are divided into strong, average And weak. According to the degree of dissociation, those with solutions > 30% are considered strong electrolytes; weak electrolytes are< 3%, к средним – 3% 30%. Сила электролита – величина, зависящая от концентрации вещества, температуры, природы растворителя и др.
In the case of aqueous solutions strong electrolytes(> 30%) include the following groups of compounds.
1 . Many inorganic acids, such as hydrochloric HCl, nitric HNO 3, sulfuric H 2 SO 4 in dilute solutions. The strongest inorganic acid is perchloric HClO 4.
The strength of non-oxygen acids increases in a series of similar compounds when moving down the subgroup of acid-forming elements:

HCl – HBr – HI.

Hydrofluoric acid HF dissolves glass, but this does not at all indicate its strength. This oxygen-free halogen-containing acid is classified as an acid of medium strength due to the high H–F bond energy, the ability of HF molecules to combine (associate) due to strong hydrogen bonds, the interaction of F – ions with HF molecules (hydrogen bonds) with the formation of ions and other more complex particles. As a result, the concentration of hydrogen ions in an aqueous solution of this acid is significantly reduced, so hydrofluoric acid is considered to be of medium strength.
Hydrogen fluoride reacts with silicon dioxide, which is part of the glass, according to the equation:

SiO 2 + 4HF = SiF 4 + 2H 2 O.

Hydrofluoric acid should not be stored in glass containers. For this purpose, vessels made of lead, some plastics and glass are used, the walls of which are coated on the inside with a thick layer of paraffin. If hydrogen fluoride gas is used to “etch” glass, the surface of the glass becomes matte, which is used for applying inscriptions and various designs to the glass. “Etching” glass with an aqueous solution of hydrofluoric acid leads to corrosion of the glass surface, which remains transparent. A 40% solution of hydrofluoric acid is usually commercially available.

The strength of oxygen acids of the same type changes in the opposite direction, for example, periodic acid HIO 4 is weaker than perchloric acid HClO 4.
If an element forms several oxygen acids, then the acid in which the acid-forming element has the highest valence has the greatest strength. Thus, in the series of acids HClO (hypochlorous) – HClO 2 (chlorous) – HClO 3 (chlorous) – HClO 4 (chloric), the latter is the strongest.

One volume of water dissolves about two volumes of chlorine. Chlorine (about half of it) reacts with water:

Cl 2 + H 2 O = HCl + HСlO.

Hydrochloric acid is strong; there are practically no HCl molecules in its aqueous solution. It is more correct to write the reaction equation as follows:

Cl 2 + H 2 O = H + + Cl – + HClO – 25 kJ/mol.

The resulting solution is called chlorine water.
Hypochlorous acid is a fast-acting oxidizing agent, so it is used to bleach fabrics.

2 . Hydroxides of elements of the main subgroups of groups I and II of the periodic system: LiOH, NaOH, KOH, Ca(OH) 2, etc. When moving down the subgroup, as the metallic properties of the element increase, the strength of the hydroxides increases. Soluble hydroxides of the main subgroup of group I elements are classified as alkalis.

Alkalis are bases that are soluble in water. These also include hydroxides of elements of the main subgroup of group II (alkaline earth metals) and ammonium hydroxide (an aqueous solution of ammonia). Sometimes alkalis are those hydroxides that create a high concentration of hydroxide ions in an aqueous solution. In outdated literature, you can find among the alkalis potassium carbonates K 2 CO 3 (potash) and sodium carbonates Na 2 CO 3 (soda), sodium bicarbonate NaHCO 3 (baking soda), borax Na 2 B 4 O 7, sodium hydrosulfides NaHS and potassium KHS et al.

Calcium hydroxide Ca(OH) 2 as a strong electrolyte dissociates in one step:

Ca(OH) 2 = Ca 2+ + 2OH – .

3 . Almost all salts. Salt, if it is a strong electrolyte, dissociates in one step, for example ferric chloride:

FeCl 3 = Fe 3+ + 3Cl – .

In the case of aqueous solutions weak electrolytes ( < 3%) относят перечисленные ниже соединения.

1 . Water H 2 O is the most important electrolyte.

2 . Some inorganic and almost all organic acids: H 2 S (hydrogen sulfide), H 2 SO 3 (sulphurous), H 2 CO 3 (carbonic), HCN (hydrocyanic), H 3 PO 4 (phosphoric, orthophosphoric), H 2 SiO 3 (silicon), H 3 BO 3 (boric, orthoboric), CH 3 COOH (acetic), etc.
Note that carbonic acid does not exist in the formula H 2 CO 3. When carbon dioxide CO 2 is dissolved in water, its hydrate CO 2 H 2 O is formed, which we write for convenience of calculations as H 2 CO 3, and the dissociation reaction equation looks like this:

The dissociation of weak carbonic acid occurs in two stages. The resulting bicarbonate ion also behaves as a weak electrolyte.
Other polybasic acids dissociate in the same way: H 3 PO 4 (phosphoric), H 2 SiO 3 (silicon), H 3 BO 3 (boric). In an aqueous solution, dissociation practically occurs only in the first step. How to carry out dissociation at the last stage?
3 . Hydroxides of many elements, for example Al(OH) 3, Cu(OH) 2, Fe(OH) 2, Fe(OH) 3, etc.
All these hydroxides dissociate in an aqueous solution stepwise, for example iron hydroxide
Fe(OH) 3:

In an aqueous solution, dissociation occurs almost exclusively in the first step. How to shift the equilibrium towards the formation of Fe 3+ ions?
The basic properties of hydroxides of the same element increase with decreasing valence of the element. Thus, the basic properties of iron dihydroxide Fe(OH) 2 are more pronounced than those of trihydroxide Fe(OH) 3. This statement is equivalent to the fact that the acidic properties of Fe(OH) 3 are stronger than those of Fe(OH) 2.
4 . Ammonium hydroxide NH 4 OH.
When ammonia gas NH 3 is dissolved in water, a solution is obtained that conducts electricity very poorly and has a bitter, soapy taste. The solution medium is basic, or alkaline. This behavior of ammonia is explained as follows: When ammonia is dissolved in water, ammonia hydrate NH 3 H 2 O is formed, to which we conventionally attribute the formula of the non-existent ammonium hydroxide NH 4 OH, considering that this compound dissociates to form ammonium ion and hydroxide ion OH –:

NH 4 OH = + OH – .

5 . Some salts: zinc chloride ZnCl 2, iron thiocyanate Fe(NCS) 3, mercury cyanide Hg(CN) 2, etc. These salts dissociate stepwise.

Some people consider phosphoric acid H 3 PO 4 to be medium-strength electrolytes. We will consider phosphoric acid a weak electrolyte and write down the three stages of its dissociation. Sulfuric acid in concentrated solutions behaves as an electrolyte of medium strength, and in very concentrated solutions it behaves as a weak electrolyte. We will further consider sulfuric acid a strong electrolyte and write the equation of its dissociation in one step.

Salts, their properties, hydrolysis

8th grade student B of school No. 182

Petrova Polina

Chemistry teacher:

Kharina Ekaterina Alekseevna

MOSCOW 2009

In everyday life, we are accustomed to dealing with only one salt - table salt, i.e. sodium chloride NaCl. However, in chemistry, a whole class of compounds is called salts. Salts can be considered as products of the replacement of hydrogen in an acid with a metal. Table salt, for example, can be obtained from hydrochloric acid by a substitution reaction:

2Na + 2HCl = 2NaCl + H2.

acid salt

If you take aluminum instead of sodium, another salt is formed - aluminum chloride:

2Al + 6HCl = 2AlCl3 + 3H2

Salts- These are complex substances consisting of metal atoms and acidic residues. They are the products of complete or partial replacement of hydrogen in an acid with a metal or a hydroxyl group in a base with an acid residue. For example, if in sulfuric acid H 2 SO 4 we replace one hydrogen atom with potassium, we get the salt KHSO 4, and if two - K 2 SO 4.

There are several types of salts.

Types of salts	Definition	Examples of salts
Average	The product of complete replacement of acid hydrogen with metal. They contain neither H atoms nor OH groups.	Na 2 SO 4 sodium sulfate CuCl 2 copper (II) chloride Ca 3 (PO 4) 2 calcium phosphate Na 2 CO 3 sodium carbonate (soda ash)
Sour	A product of incomplete replacement of acid hydrogen by metal. Contain hydrogen atoms. (They are formed only by polybasic acids)	CaHPO 4 calcium hydrogen phosphate Ca(H 2 PO 4) 2 calcium dihydrogen phosphate NaHCO 3 sodium bicarbonate (baking soda)
Basic	The product of incomplete replacement of the hydroxyl groups of a base with an acidic residue. Includes OH groups. (Formed only by polyacid bases)	Cu(OH)Cl copper (II) hydroxychloride Ca 5 (PO 4) 3 (OH) calcium hydroxyphosphate (CuOH) 2 CO 3 copper (II) hydroxycarbonate (malachite)
Mixed	Salts of two acids	Ca(OCl)Cl – bleach
Double	Salts of two metals	K 2 NaPO 4 – dipotassium sodium orthophosphate
Crystalline hydrates	Contains water of crystallization. When heated, they dehydrate - they lose water, turning into anhydrous salt.	CuSO4. 5H 2 O – pentahydrate copper(II) sulfate (copper sulfate) Na 2 CO 3. 10H 2 O – sodium carbonate decahydrate (soda)

Methods for obtaining salts.

1. Salts can be obtained by acting with acids on metals, basic oxides and bases:

Zn + 2HCl ZnCl 2 + H 2

zinc chloride

3H 2 SO 4 + Fe 2 O 3 Fe 2 (SO 4) 3 + 3H 2 O

iron(III) sulfate

3HNO 3 + Cr(OH) 3 Cr(NO 3) 3 + 3H 2 O

chromium(III) nitrate

2. Salts are formed by the reaction of acidic oxides with alkalis, as well as acidic oxides with basic oxides:

N 2 O 5 + Ca(OH) 2 Ca(NO 3) 2 + H 2 O

calcium nitrate

SiO 2 + CaO CaSiO 3

calcium silicate

3. Salts can be obtained by reacting salts with acids, alkalis, metals, non-volatile acid oxides and other salts. Such reactions occur under the conditions of evolution of gas, precipitation of a precipitate, evolution of an oxide of a weaker acid, or evolution of a volatile oxide.

Ca 3 (PO4) 2 + 3H 2 SO 4 3CaSO 4 + 2H 3 PO 4

calcium orthophosphate calcium sulfate

Fe 2 (SO 4) 3 + 6NaOH 2Fe(OH) 3 + 3Na 2 SO 4

iron (III) sulfate sodium sulfate

CuSO 4 + Fe FeSO 4 + Cu

copper (II) sulfate iron (II) sulfate

CaCO 3 + SiO 2 CaSiO 3 + CO 2

calcium carbonate calcium silicate

Al 2 (SO 4) 3 + 3BaCl 2 3BaSO 4 + 2AlCl 3

sulfate chloride sulfate chloride

aluminum barium barium aluminum

4. Salts of oxygen-free acids are formed by the interaction of metals with non-metals:

2Fe + 3Cl 2 2FeCl 3

iron(III) chloride

Physical properties.

Salts are solids of various colors. Their solubility in water varies. All salts of nitric and acetic acids, as well as sodium and potassium salts, are soluble. The solubility of other salts in water can be found in the solubility table.

Chemical properties.

1) Salts react with metals.

Since these reactions occur in aqueous solutions, Li, Na, K, Ca, Ba and other active metals that react with water under normal conditions cannot be used for experiments, or reactions cannot be carried out in a melt.

CuSO 4 + Zn ZnSO 4 + Cu

Pb(NO 3) 2 + Zn Zn(NO 3) 2 + Pb

2) Salts react with acids. These reactions occur when a stronger acid displaces a weaker one, releasing gas or precipitating.

When carrying out these reactions, they usually take dry salt and act with concentrated acid.

BaCl 2 + H 2 SO 4 BaSO 4 + 2HCl

Na 2 SiO 3 + 2HCl 2NaCl + H 2 SiO 3

3) Salts react with alkalis in aqueous solutions.

This is a method of obtaining insoluble bases and alkalis.

FeCl 3 (p-p) + 3NaOH(p-p) Fe(OH) 3 + 3NaCl

CuSO 4 (p-p) + 2NaOH (p-p) Na 2 SO 4 + Cu(OH) 2

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

4) Salts react with salts.

The reactions take place in solutions and are used to obtain practically insoluble salts.

AgNO 3 + KBr AgBr + KNO 3

CaCl 2 + Na 2 CO 3 CaCO 3 + 2NaCl

5) Some salts decompose when heated.

A typical example of such a reaction is the firing of limestone, the main component of which is calcium carbonate:

CaCO 3 CaO + CO2 calcium carbonate

1. Some salts are capable of crystallizing to form crystalline hydrates.

Copper (II) sulfate CuSO 4 is a white crystalline substance. When it is dissolved in water, it heats up and a blue solution is formed. The release of heat and color changes are signs of a chemical reaction. When the solution is evaporated, crystalline hydrate CuSO 4 is released. 5H 2 O (copper sulfate). The formation of this substance indicates that copper (II) sulfate reacts with water:

CuSO 4 + 5H 2 O CuSO 4 . 5H 2 O + Q

white blue-blue

Use of salts.

Most salts are widely used in industry and in everyday life. For example, sodium chloride NaCl, or table salt, is indispensable in cooking. In industry, sodium chloride is used to produce sodium hydroxide, soda NaHCO 3, chlorine, sodium. Salts of nitric and orthophosphoric acids are mainly mineral fertilizers. For example, potassium nitrate KNO 3 is potassium nitrate. It is also part of gunpowder and other pyrotechnic mixtures. Salts are used to obtain metals, acids, and in glass production. Many plant protection products from diseases, pests, and some medicinal substances also belong to the class of salts. Potassium permanganate KMnO 4 is often called potassium permanganate. Limestone and gypsum – CaSO 4 – are used as building materials. 2H 2 O, which is also used in medicine.

Solutions and solubility.

As stated earlier, solubility is an important property of salts. Solubility is the ability of a substance to form with another substance a homogeneous, stable system of variable composition, consisting of two or more components.

Solutions- These are homogeneous systems consisting of solvent molecules and solute particles.

So, for example, a solution of table salt consists of a solvent - water, a dissolved substance - Na +, Cl - ions.

Ions(from Greek ión - going), electrically charged particles formed by the loss or gain of electrons (or other charged particles) by atoms or groups of atoms. The concept and term “ion” was introduced in 1834 by M. Faraday, who, while studying the effect of electric current on aqueous solutions of acids, alkalis and salts, suggested that the electrical conductivity of such solutions is due to the movement of ions. Faraday called positively charged ions moving in solution towards the negative pole (cathode) cations, and negatively charged ions moving towards the positive pole (anode) - anions.

Based on the degree of solubility in water, substances are divided into three groups:

1) Highly soluble;

2) Slightly soluble;

3) Practically insoluble.

Many salts are highly soluble in water. When deciding on the solubility of other salts in water, you will have to use the solubility table.

It is well known that some substances, when dissolved or molten, conduct electric current, while others do not conduct current under the same conditions.

Substances that disintegrate into ions in solutions or melts and therefore conduct electric current are called electrolytes.

Substances that, under the same conditions, do not disintegrate into ions and do not conduct electric current are called non-electrolytes.

Electrolytes include acids, bases and almost all salts. Electrolytes themselves do not conduct electricity. In solutions and melts, they break up into ions, which is why current flows.

The breakdown of electrolytes into ions when dissolved in water is called electrolytic dissociation. Its content boils down to the following three provisions:

1) Electrolytes, when dissolved in water, break up (dissociate) into ions - positive and negative.

2) Under the influence of an electric current, ions acquire directional movement: positively charged ions move towards the cathode and are called cations, and negatively charged ions move towards the anode and are called anions.

3) Dissociation is a reversible process: in parallel with the disintegration of molecules into ions (dissociation), the process of combining ions (association) occurs.

reversibility

Strong and weak electrolytes.

To quantitatively characterize the ability of an electrolyte to disintegrate into ions, the concept of the degree of dissociation (α), t . E. The ratio of the number of molecules disintegrated into ions to the total number of molecules. For example, α = 1 indicates that the electrolyte has completely disintegrated into ions, and α = 0.2 means that only every fifth of its molecules has dissociated. When a concentrated solution is diluted, as well as when heated, its electrical conductivity increases, as the degree of dissociation increases.

Depending on the value of α, electrolytes are conventionally divided into strong (dissociate almost completely, (α 0.95)) medium strength (0.95

Strong electrolytes are many mineral acids (HCl, HBr, HI, H 2 SO 4, HNO 3, etc.), alkalis (NaOH, KOH, Ca(OH) 2, etc.), and almost all salts. Weak ones include solutions of some mineral acids (H 2 S, H 2 SO 3, H 2 CO 3, HCN, HClO), many organic acids (for example, acetic acid CH 3 COOH), an aqueous solution of ammonia (NH 3. 2 O), water, some mercury salts (HgCl 2). Electrolytes of medium strength often include hydrofluoric HF, orthophosphoric H 3 PO 4 and nitrous HNO 2 acids.

Hydrolysis of salts.

The term "hydrolysis" comes from the Greek words hidor (water) and lysis (decomposition). Hydrolysis is usually understood as an exchange reaction between a substance and water. Hydrolytic processes are extremely common in the nature around us (both living and nonliving), and are also widely used by humans in modern production and household technologies.

Salt hydrolysis is the reaction of interaction between the ions that make up the salt and water, which leads to the formation of a weak electrolyte and is accompanied by a change in the solution environment.

Three types of salts undergo hydrolysis:

a) salts formed by a weak base and a strong acid (CuCl 2, NH 4 Cl, Fe 2 (SO 4) 3 - hydrolysis of the cation occurs)

NH 4 + + H 2 O NH 3 + H 3 O +

NH 4 Cl + H 2 O NH 3 . H2O+HCl

The reaction of the medium is acidic.

b) salts formed by a strong base and a weak acid (K 2 CO 3, Na 2 S - hydrolysis occurs at the anion)

SiO 3 2- + 2H 2 O H 2 SiO 3 + 2OH -

K 2 SiO 3 +2H 2 O H 2 SiO 3 +2KOH

The reaction of the medium is alkaline.

c) salts formed by a weak base and a weak acid (NH 4) 2 CO 3, Fe 2 (CO 3) 3 - hydrolysis occurs at the cation and at the anion.

2NH 4 + + CO 3 2- + 2H 2 O 2NH 3. H2O + H2CO3

(NH 4) 2 CO 3 + H 2 O 2NH 3. H2O + H2CO3

Often the reaction of the environment is neutral.

d) salts formed by a strong base and a strong acid (NaCl, Ba(NO 3) 2) are not subject to hydrolysis.

In some cases, hydrolysis proceeds irreversibly (as they say, it goes to the end). So, when mixing solutions of sodium carbonate and copper sulfate, a blue precipitate of hydrated basic salt precipitates, which, when heated, loses part of the water of crystallization and acquires a green color - it turns into anhydrous basic copper carbonate - malachite:

2CuSO 4 + 2Na 2 CO 3 + H 2 O (CuOH) 2 CO 3 + 2Na 2 SO 4 + CO 2

When mixing solutions of sodium sulfide and aluminum chloride, hydrolysis also proceeds to completion:

2AlCl 3 + 3Na 2 S + 6H 2 O 2Al(OH) 3 + 3H 2 S + 6NaCl

Therefore, Al 2 S 3 cannot be isolated from an aqueous solution. This salt is obtained from simple substances.