All strong and weak electrolytes Table. Solutions. El-lithic dissociation theory

Strong electrolytes when dissolved in water are almost completely dissociated on ions, regardless of their concentration in the solution.

Therefore, in the dissociation equations of strong electrolytes put a sign of equality (\u003d).

Strong electrolytes include:

Soluble salts;

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

The bases formed by alkaline metals (Lioh, NaOH, KOH, etc.) and alkaline earth metals (Ca (OH) 2, SR (OH) 2, BA (OH) 2).

Weak electrolytes in aqueous solutions are only partially (reversible) dissociated on ions.

Therefore, in the dissociation equations of weak electrolytes put a sign of reversibility (⇄).

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 equations reactions

Ionic equations reactions
Chemical reactions in electrolyte solutions (acids, bases and salts) occur with the participation of ions. The final solution can remain transparent (products are well soluble in water), but one of the product will be a weak electrolyte; In other cases, there will be a precipitation or gas selection.

For reactions in solutions with the participation of ions, not only the molecular equation, but also full ion and brief ionic.
In ionic equations at the suggestion of the French Chemist K. -l. Bertoll (1801) All strong well-soluble electrolytes are recorded in the formula of ions, and precipitation, gases and weak electrolytes are in the form of molecular formulas. The formation of precipitation mark the "Arrow down" sign (↓), the formation of gases is the "Arrow up" sign (). An example of the recording of the reaction equation according to Burtoll rule:

a) molecular equation
Na2CO3 + H2SO4 \u003d Na2SO4 + CO2 + H2O
b) full ion equation
2NA + + CO32- + 2H + + SO42- \u003d 2NA + + SO42- + CO2 + H2O
(CO2 - gas, H2O - weak electrolyte)
c) brief ion equation
CO32- + 2H + \u003d CO2 + H2O

Typically, when recording is limited to a brief ion equation, the solids-reagents are denoted by the index (T), the gas reagents - the index (g). Examples:

1) Cu (OH) 2 (T) + 2HNO3 \u003d Cu (NO3) 2 + 2H2O
Cu (OH) 2 (T) + 2H + \u003d Cu2 + + 2H2O
Cu (OH) 2 almost insoluble in water
2) BAS + H2SO4 \u003d BASO4 ↓ + H2S
Ba2 + + S2- + 2H + + SO42- \u003d Baso4 ↓ + H2S
(Complete and short ion equations are the same)
3) Caco3 (T) + CO2 (g) + H2O \u003d Ca (HCO3) 2
Caco3 (T) + CO2 (g) + H2O \u003d CA2 + + 2HCO3-
(Most acid salts are well soluble in water).

If strong electrolytes are involved in the reaction, the ion type of equation is absent:

Mg (OH) 2 (T) + 2HF (P) \u003d MGF2 ↓ + 2H2O

Ticket number 22.

Hydrolysis of salts

The hydrolysis of salts is the interaction of salt ions with water to form lowly subsoous particles.

Hydrolysis, literally, is water decomposition. Giving such a definition of the hydrolysis of salts, we emphasize that salts in the solution are in the form of ions, and that the driving force of the reaction is the formation of smallssaging particles (general rule for many reactions in solutions).

Hydrolysis occurs only in cases where the ions resulting from the electrolytic dissociation of the salt - the cation, anion, or both together, are capable of forming weakly dissolve compounds with water ions, and this, in turn, occurs when the cation is strongly polarizing ( The cation of a weak base), and anion - easily polarizes (anion of weak acid). It changes the pH of the medium. If the cation forms a strong base, and the anion is strong acid, they are not exposed to hydrolysis.

1. Hydrolysis of the salts of weak base and severe acid It passes through the cation, while the weak base or the main salt and the pH of the solution will decrease

2. Hydrolysis of salts of weak acid and strong base passes through anion, while weak acid or acidic salt and pH solution will increase

3. Hydrolysis of the salts of a weak base and weak acid usually runs aimed with the formation of weak acid and a weak base; The pH of the solution is slightly different from 7 and is determined by the relative force of the acid and the base

4. Hydrolysis salts of a strong base and strong acid does not proceed

Question 24 classification of oxides

Oxidescomplex substances are called, the molecules of which include oxygen atoms in the steppe oxidation - 2 and some other element.

Oxides.it can be obtained with the direct interaction of oxygen with another element and indirectly (for example, with decomposition of salts, bases, acids). Under normal conditions, oxides are in a solid, liquid and gaseous state, this type of compounds are very common in nature. Oxides are contained in the earth's crust. Rust, sand, water, carbon dioxide are oxides.

Saline-forming oxides For example,

Cuo + 2HCl → CUCL 2 + H 2 O.

Cuo + SO 3 → CUSO 4.

Saline-forming oxides- These are such oxides, which as a result of chemical reactions form salts. These are oxides of metals and non-metals, which, when interacting with water, form appropriate acids, and when interacting with bases, corresponding acidic and normal salts. For example, Copper oxide (CUO) is salt-forming oxide, because, for example, when interacting with hydrochloric acid (HCl), 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-self-forming oxides They are called such oxides that do not form salts. An example is CO, N 2 O, NO.

Strong and weak electrolytes

Acids, bases and salts in aqueous solutions are dissociated - disintegrate into ions. This process can be reversible or irreversible.

With irreversible dissociation in solutions, all substance or almost everything falls into ions. This is characteristic of strong electrolytes (Fig. 10.1, and, p. 56). Some acids and all soluble salts and bases (alkaline and alkaline earth hydroxides) (Scheme 5, p. 56) include soluble electrolytes.

Fig. 10.1. Comparison of the number of ions in solutions with the same initial amount of electrolyte: A - chloride acid (strong electrolyte); b - nitrite acid

(weak electrolyte)

Scheme 5. Classification of electrolytes by force

When the dissociation is reversible, two opposite process flows: simultaneously with the decay of the substance on ions (dissociation) there is a reverse process of combining ions in the substance molecules (association). Due to this, a part of the substance in the solution exists in the form of ions, and part - in the form of molecules (Fig. 10.1, b). Electrolytes,

which when dissolved in water, disintegrate only partially, is called weak electrolytes. These include water, many acids, as well as insoluble hydroxides and salts (scheme 5).

In the dissociation equations of weak electrolytes, instead of a conventional arrow record a bidirectional arrow (reversibility sign):

The power of the electrolytes can be explained by the polarity of the chemical bond, which is broken upon dissociation. The more polar communication, the easier the water molecules, it turns into ionic, therefore, the stronger the electrolyte. In salts and hydroxides, the polarity of communication is the largest, since there is an ionic connection between the ionic elements and hydroxide ions, therefore all soluble salts and bases are strong electrolytes. In oxygen-containing acids during dissociation, the connection of O - H is broken, the polarity of which depends on the qualitative and quantitative composition of the acid residue. The force of most oxygen-containing acids can be determined if the usual acid formula is written as E (OH) M O n. If this formula is N< 2 — кислота слабая, если n >2 - Strong.

The dependence of acids from the composition of the acid residue

The degree of dissociation

The power of the electrolytes quantitatively characterizes the degree of electrolytic dissociation A, showing the share of molecules of substances that broke up in the solution on ions.

The degree of dissociation A is equal to the ratio of the number of m molecules n or the amount of the substance N, which has been impaved on the ions, to the total number of molecules N 0 or the amount of dissolved substance N 0:

The degree of dissociation can be expressed not only in the fractions of the unit, but also in percent:

The value A may vary from 0 (there is no dissociation) to 1, or 100% (complete dissociation). The better the electrolyte decays, the greater the value of the degree of dissociation.

According to the value of the degree of electrolytic dissociation, electrolytes are often separated by no two, but into three groups: strong, weak and electrolytes of the middle force. Those strong electrolytes consider the degree of dissociation of which more than 30%, and weak with a degree of less than 3%. Electrolytes with intermediate values \u200b\u200bA - from 3% to 30% - called medium power electrolytes. For this classification, acids are considered: HF, HNO 2, H 3 PO 4, H 2 SO 3 and some others. The two recent acids are medium power electrolytes only at the first stage of dissociation, and in others it is weak electrolytes.

The degree of dissociation is the variable value. It depends not only on the nature of the electrolyte, but also on its concentration in solution. This dependence first identified and explored Wilhelm Ostvald. Today, it is called the law of reducing Ostvald: when the solution is diluted with water, as well as with increasing temperature, the degree of dissociation increases.

Calculation of the degree of dissociation

Example. In one liter of water dissolved hydrogen fluoride with the amount of substance 5 mol. The resulting solution contains 0.06 mol hydrogen ions. Determine the degree of dissociation of fluoride acid (as a percentage).

We write the fluoride acid dissociation equation:

During dissociation from one acid molecule, one hydrogen ion is formed. If the solution contains 0.06 mol H + ions, this means that the predsissorate-Valo 0.06 mole of the hydrogen fluoride molecules. Consequently, the degree of dissociation is:

An outstanding German physico-chemist, the Nobel Prize winner in 1909 Chemistry. Born in Riga, studied at the University of Derpta, where he began teaching and scientific activities. At 35, he moved to Leipzig, where he was headed by the Physics and Chemical Institute. He studied the laws of chemical equilibrium, the properties of solutions, discovered the law of breeding called by his name, developed the foundations of the theory of acid-base catalysis, a lot of time paid the history of chemistry. He founded the world's first department of physical chemistry and the first physico-chemical magazine. In personal life possessed strange habits: he felt disgust for the haircut, and with his secretary communicated exclusively with the help of a bicycle call.

Key idea

Dissociation of weak electrolytes - reversible process, and strong -

irreversible.

Control questions

116. Give the definition of strong and weak electrolytes.

117. Give examples of strong and weak electrolytes.

118. What size is used for the quantitative characteristic of the power of the electrolyte? Is it constant in any solutions? How can I increase the degree of electrolyte dissociation?

Tasks for mastering the material

119. Give one example of salt, acid and bases that are: a) with a strong electrolyte; b) weak electrolyte.

120. Give an example of a substance: a) a two-axis acid, which in the first stage is an electrolyte of the middle force, and on the second - weak electrolyte; b) two-axis acid, which on both stages is a weak electrolyte.

121. In some acid at the first stage, the dissociation degree is 100%, and in the second - 15%. What acid can it be?

122. What kind of particles are larger in the sulfide hydrogen solution: molecules H 2 S, H + ions, S 2 ions or HS ions -?

123. From the above list of substances separately, write out the formula: a) strong electrolytes; b) weak electrolytes.

NaCl, HCl, NaOH, Nano 3, HNO 3, HNO 2, H 2 SO 4, BA (OH) 2, H 2 S, K 2 S, PB (NO 3) 2.

124. Make the equation of dissociation of strontium nitrate, Mercury (11) chloride, calcium carbonate, calcium hydroxide, sulfide acid. In what cases does dissociation be reversible?

125. In an aqueous sodium sulfate solution contains 0.3 mol ions. What mass of this salt was used to prepare such a solution?

126. In the solution of hydrogen fluoride, 1 liter contains 2 g of this acid, and the amount of substance of hydrogen ions is 0.008 mol. What is the amount of fluoride ion substances in this solution?

127. In three tubes, the same volumes of chloride, fluoride and sulfide acid solutions are contained. In all test tubes of the amount of substance, the acids are equal. But in the first test tube, the amount of substance of hydrogen ions is 3. 10 -7 mol, in the second - 8. 10 -5 mol, and in the third - 0.001 mol. Which tube contains each acid?

128. The first test tube contains an electrolyte solution, the degree of dissociation of which is 89%, in the second - electrolyte with a dissociation of 8% o, and in the third - 0.2% of. Bring two examples of electrolytes of different classes of compounds that may be contained in these test tubes.

129 *. In additional sources, find information on the dependence of the power of electrolytes from the nature of substances. Set the relationship between the structure of substances, the nature of the chemical elements that form them and the power of electrolytes.

This is the material of the textbook

All substances can be divided into electrolytes and non-electrolytes. The electrolytes includes substances, solutions or melts of which electric current (for example, aqueous solutions or melts KCl, H 3 PO 4, Na 2 CO 3). Substances of non-electro-cells when melting or dissolving electric currents are not conducted (sugar, alcohol, acetone, etc.).

Electrolytes are divided into strong and weak. Strong electrolytes in solutions or melts are completely dissociated on ions. When writing the equations of chemical reactions, this is emphasized with an arrow in one direction, for example:

HCl → H + + Cl -

Ca (OH) 2 → CA 2+ + 2OH -

Silent electrolytes include substances with a heteropolar or ionic crystal structure (Table 1.1).

Table 1.1 Strong electrolytes

Weak electrolytes on ions disintegrate only partially. Along with ions in melts or solutions of these substances, substances are present in the overwhelming majority are not dissociated molecules. In solutions of weak electrolytes, in parallel with dissociation proof process is the association, i.e. the connection of ions in the molecule. When recording the reaction equation, this is emphasized by two opposite directed arrows.

CH 3 COOH D CH 3 COO - + H +

Weak electrolytes include substances with a homeopolar type of crystal lattice (Table 1.2).

Table 1.2 Weak electrolytes

The equilibrium state of weak electrolyte in aqueous solution is quantitatively characterized by the degree of electrolytic dissociation and the constant of electrolytic dissociation.

The degree of electrolytic dissociation α is the ratio of the number of molecules encountered to ions to the total number of dissolved electrolyte molecules:

The degree of dissociation shows which part of the total amount of dissolved electrolyte disintegrates on the ions and depends on the nature of the electrolyte and the solvent, as well as on the concentration of the substance in the solution, has a dimensionless value, although it is usually expressed as a percentage. With infinite dilution of the electrolyte solution, the degree of dissociation is approaching a unit, which corresponds to the full, 100%, dissociation of the molecules of the dissolved substance to the ions. For solutions of weak electrolytes α<<1. Сильные электролиты в растворах диссоциируют полностью (α =1). Если известно, что в 0,1 М растворе уксусной кислоты степень электрической диссоциации α =0,0132, это означает, что 0,0132 (или 1,32%) общего количества растворённой уксусной кислоты продиссоциировало на ионы, а 0,9868 (или 98,68%) находится в виде недиссоциированных молекул. Диссоциация слабых электролитов в растворе подчиняется закону действия масс.

In general, the reversible chemical reaction can be represented as:

a.A +. b.B D. d.D +. e.E.

The reaction rate is directly proportional to the product of the concentration of reacting particles in the degrees of their stoichiometric coefficients. Then for direct reaction

V 1 \u003d. k. 1 [A] A.[B] b,

and the rate of reverse reaction

V 2 \u003d. k. 2 [D] D.[E] e.

At some point in time, the speed of direct and reverse reaction is leveled, i.e.

This condition is called chemical equilibrium. From here

k. 1 [A] A.[B] B.= K. 2 [D] D.[E] E.

Grouped constant values \u200b\u200bon the one hand, and variables, on the other hand, we obtain:

Thus, for a reversible chemical reaction in a state of equilibrium, the product of equilibrium concentrations of reaction products in the degrees of their stoichiometric coefficients, referred to the same product for the starting materials there is a permanent value under these temperature and pressure. Numerical value of a chemical equilibrium constant TO It does not depend on the concentration of reactant substances. For example, the equilibrium constant of the dissociation of nitrogen acid in accordance with the law of the mass can be written as:

HNO 2 + H 2 OD H 3 O + + NO 2 -

Magnitude To A. They refer to the dissociation constant of the acid, in this case nitrogenous.

The constant of the dissociation of a weak base is also expressed. For example, for ammonia dissociation reaction:

NH 3 + H 2 O DNH 4 + + OH -

Magnitude To B. They refer to the constant of the dissociation of the base, in this case ammonia. The higher the electrolyte dissociation constant, the stronger the electrolyte dissociates and the higher the concentration of its ions in the solution in equilibrium. There is a relationship between the degree of dissociation and the constant of dissociation of weak electrolyte:

This is a mathematical expression of an ostel dilution law: when the weak electrolyte is diluted, the degree of its dissociation increases. For weak electrolytes with TO≤1 ∙ 10 -4 and FROM ≥0.1 mol / l use simplified expression:

TO= α 2 ∙FROMor α.

Example1. Calculate the degree of dissociation and the concentration of ions and [NH 4 +] in 0.1 M ammonium hydroxide solution if TO NH 4 OH \u003d 1.76 ∙ 10 -5

Dano: NH 4 Oh

TO NH 4 OH \u003d 1.76 ∙ 10 -5

Decision:

Since the electrolyte is quite weak ( To NH 4 Oh =1,76∙10 –5 <1∙ 10 - 4) и раствор его не слишком разбавлен, можно принять, что:

or 1.33%

The concentration of ions in the binary electrolyte solution is equal to C.∙ α, since the binary electrolyte is ionized with the formation of one cation and one anion, then \u003d [NH 4 +] \u003d 0.1 ∙ 1,33 ∙ 10 -2 \u003d 1.33 ∙ 10 -3 (mol / l).

Answer: α \u003d 1.33%; \u003d [NH 4 +] \u003d 1.33 ∙ 10 -3 mol / l.

Theory of strong electrolyte

Strong electrolytes in solutions and melts are completely dissociated on ions. However, experimental studies of electrical conductivity of solutions of strong electrolytes show that its value is somewhat underestimated compared to that electrical conductivity that should be at 100% dissociation. Such a mismatch is explained by the theory of strong electrolytes proposed by Debay and Gukkel. According to this theory, there is electrostatic interaction in solutions of strong electrolytes between ions. A "ion atmosphere" is formed around each ion from the ions of the opposite sign of the charge, which slows down the movement of ions in the solution by passing a constant electric current. In addition to electrostatic interaction of ions, in concentrated solutions, the ions association should be taken into account. The effect of the mehylic forces creates the effect of incomplete dissociation of molecules, i.e. seeming dissociation degree. The value of α defined on the experiment is always somewhat lower than the true α. For example, in 0.1 M solution of Na 2 SO 4, the experimental value α \u003d 45%. To account for electrostatic factors in solutions of strong electrolytes, use the concept of activity (but). The activity of the ion is called an effective or apparent concentration according to which the ion acts in solution. Activity and true concentration are related to the expression:

where f - The activity coefficient that characterizes the degree of deviation of the system from ideal due to electrostatic interactions of ions.

The activity coefficients of ions depend on the value of μ, called the ionic power of the solution. The ionic force of the solution is a measure of the electrostatic interaction of all ions present in the solution and equal to the amount of concentrations (from) each of the ions present in the square of its charging number (z):

In dilute solutions (μ<0,1М) коэффициенты активности меньше единицы и уменьшаются с ростом ионной силы. Растворы с очень низкой ионной силой (µ < 1∙10 -4 М) можно считать идеальными. В бесконечно разбавленных растворах электролитов активность можно заменить истинной концентрацией. В идеальной системе a \u003d C. And the activity coefficient is 1. This means that electrostatic interactions are practically absent. In very concentrated solutions (μ\u003e 1M), the coefficients of the activity of ions may be more than one. The relationship of the coefficient of activity with the ionic power of the solution is expressed by formulas:

for µ <10 -2

at 10 -2 ≤ µ ≤ 10 -1

+ 0,1Z 2 μ. at 0.1.<µ <1

The equilibrium constant, expressed through activity, is called thermodynamic. For example, for reaction

a.A +. b.B. d.D +. e.E.

the thermodynamic constant has the form:

It depends on the temperature, pressure and nature of the solvent.

Since the activity of the particle, then

where TO C - Constant equilibrium constant.

Value TO C depends not only on temperature, nature of the solvent and pressure, but also from ion power m.. Since thermodynamic constants depend on the smallest number of factors, then, therefore, are the most fundamental characteristics of equilibrium. Therefore, the directories provide precisely thermodynamic constants. The magnitudes of the thermodynamic constants of some weak electrolytes are given in the application of this manual. \u003d 0.024 mol / l.

With the increasing charge of the ion, the activity coefficient and the activity of the ion decreases.

Questions for self-control:

What is the perfect system? Name the main reasons for the rejection of the real system from the ideal.
What do they call the degree of dissociation of electrolytes?
Give examples of strong and weak electrolytes.
What interconnection exists between dissociation constant and the degree of dissociation of weak electrolyte? Express it mathematically.
What is activity? How are the activity of the ion and its true concentration?
What is the activity coefficient?
How does the charge of ion affect the value of the activity coefficient?
What is the ion power of the solution, its mathematical expression?
Record the formula to calculate the coefficients of the activity of individual ions depending on the ionic force of the solution.
Word the law action of the masses and express it mathematically.
What is the thermodynamic equilibrium constant? What factors affect its magnitude?
What is the concentration constant equilibrium? What factors affect its magnitude?
How are the thermodynamic and concentration constant equilibrium?
What limits may change the values \u200b\u200bof the activity coefficient?
What are the main provisions of the theory of strong electrolytes?

Salts, their properties, hydrolysis

Pupil 8th grade B school number 182

Petrova Polina.

Chemistry Teacher:

Harina Ekaterina Alekseevna

Moscow 2009.

In everyday life we \u200b\u200bused to deal with only one salt - cooking, i.e. Sodium chloride NaCl. However, in chemistry, the salts are called a whole class of compounds. Salts can be viewed as hydrogen substitution products in acid for metal. The table salt, for example, can be obtained from hydrochloric acid by reaction reaction:

2NA + 2HCl \u003d 2NACl + H 2.

acid Sol

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

2AL + 6HCl \u003d 2AlCl 3 + 3H 2

Sololi. - These are complex substances consisting of metals and acid residual atoms. They are products of complete or partial substitution of hydrogen in acid for metal or hydroxyl group at the base to the acid residue. For example, if in sulfuric acid H 2 SO 4 to replace one hydrogen atom, we obtain the KHSO 4 salt, and if two - k 2 SO 4.

Distinguish several types of salts.

Types of salts	Definition	Examples of salts
Middle	Product of complete substitution of hydrogen acid for metal. Neither atoms N n n-group contain.	Na 2 SO 4 sodium sulfate CUCl 2 Copper chloride (II) Ca 3 (PO 4) 2 Calcium phosphate Na 2 CO 3 sodium carbonate (soda calcined)
Sour	Product of incomplete replacement of hydrogen acid for metal. Contain in its composition atoms of hydrogen. (They are only educated acids)	CAHPO 4 Calcium Hydrophosphate CA (H 2 PO 4) 2 Calcium Dihydrophosphate NaHCO 3 Sodium Barbonate (Drinking Soda)
Maintenance	The product of incomplete substitution of hydroxogroups of the base to the acid residue. Include in-group. (Formed only by multi-acid bases)	Cu (OH) Cl COP hydroxochloride (II) Ca 5 (PO 4) 3 (OH) calcium hydroxphosphate (CuOH) 2 CO 3 copper hydroxocarbonate (II) (Malachite)
Mixed	Salts of two acids	CA (OCL) CL - chlorine lime
Double	Salts of two metals	K 2 NAPO 4 - Orthophosphate Dicalia Sodium
Crystal hydrates	Contain crystallization water. When heated, they are dehydrated - losing water, turning into anhydrous salt.	Cuso 4. 5H 2 O is the fifty copper sulfate (II) (copper sulphate) Na 2 CO 3. 10h 2 O - TIRTHDOW Sodium Carbonate (Soda)

Methods for obtaining salts.

1. Salts can be obtained by acting by acids on metals, main 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 sulfate (III)

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

chromium Nitrate (III)

2. The salts are formed in the reaction of acid oxides with alkalis, as well as acidic oxides with main 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 proceed under the condition of gas isolation, precipitation falling, isolating the oxide of weaker acid or the separation of volatile oxide.

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

calcium sulfate calcium orthophosphate

Fe 2 (SO 4) 3 + 6NAOH 2FE (OH) 3 + 3NA 2 SO 4

iron sulfate (III) sodium sulfate

Cuso 4 + Fe Feso 4 + Cu

copper Sulfate (II) Iron Sulfate (II)

Caco 3 + SiO 2 Casio 3 + Co 2

calcium silicate calcium carbonate

Al 2 (SO 4) 3 + 3BaCL 2 3 3Baso 4 + 2AlCl 3

sulfate chloride sulfate chloride

aluminum Barium Barium Aluminum

4. Salts of oxygenic acids are formed when the interaction of metals with non-metals:

2fe + 3CL 2 2FeCl 3

iron chloride (III)

Physical properties.

Salts are solids of various colors. The solubility in the water is different. All salts of nitric and acetic acids are soluble, as well as sodium and potassium salts. On solubility in water of other salts, you can learn from the solubility table.

Chemical properties.

1) Salts react with metals.

Since these reactions flow in aqueous solutions, Li, Na, K, Ca, Ba and other active metals cannot be used for experiments, which under normal conditions react with water or carry out reactions in the melt.

CUSO 4 + ZN ZNSO 4 + CU

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

2) Salts react with acids. These reactions proceed when stronger acid displaces a weaker, and the gas is released or the precipitate falls.

During these reactions, a dry salt is usually taken 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 way to obtain 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.

Reactions proceed 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 are decomposed when heated.

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

Caco 3 Cao + CO2 Calcium Carbonate

1. Some salts are capable of crystallize with the formation of crystallohydrates.

Copper sulfate (II) CUSO 4 is a white crystalline substance. When it dissolves in water, heating occurs and a solution of blue color is formed. Selection of heat and color change - these are signs of a chemical reaction. When evaporation of the solution, CUSO 4 crystalline is allocated. 5H 2 O (copper sulphate). The formation of this substance indicates that copper sulfate (II) reacts with water:

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

white blue blue color

The use of salts.

Most salts are widely used in industry and in everyday life. For example, sodium chloride NaCl, or table salt, indispensable in cooking. In industry, sodium chloride is used to obtain sodium hydroxide, NaHCO 3 soda, chlorine, sodium. Salts of nitric and orthophosphoric acids are mainly mineral fertilizers. For example, Kali Nitrate KNO 3 - Potash Selith. It also is part of powder and other pyrotechnic blends. Salts are used to obtain metals, acids, in glass production. Many plant protection products from diseases, pests, some medicinal substances also belong to the salting class. Permanganate potassium KMNO 4 is often called manganese. Limestones and gypsum - CASO 4 are used as a building material. 2H 2 O, which is also used in medicine.

Solutions and solubility.

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

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

For example, a solution of the cooking salt consists of a solvent - water, a dissolved substance - Na +, Cl - ions.

Ions (from Greek. ión - coming), electrically charged particles formed by loss or addition of electrons (or other charged particles) atoms or groups of atoms. The concept and term "ion" was introduced in 1834 M. Faraday, which, studying the effect of electric current into aqueous solutions of acids, alkalis and salts, suggested that the electrical conductivity of such solutions is due to the movement of ions. Positively charged ions moving in solution to the negative pole (cathode), Faradays called cations, and negatively charged moving to the positive pole (anode), anions.

According to the degree of solubility in water, the substances are divided into three groups:

1) well soluble;

2) low-soluble;

3) practically insoluble.

Many salts are well soluble in water. When solving the question of solubility in water, other salts will have to use the solubility table.

It is well known that some substances in a dissolved or molten form are conducted by electric current, others are not conducted in the same conditions.

Substances decaying on ions in solutions or melts and therefore conductive electric current call electrolyte.

Substances that in the same conditions on the ions are not disintegrated and the electric current is not conducted, called non-electroliths.

The electrolytes includes acids, bases and almost all salts. Electric currents themselves are not conducted. In solutions and melts, they disintegrate into ions, due to which the current flows.

The decay of electrolytes on ions when dissolved in water is called electrolytic dissociation. Its content comes down to three following provisions:

1) Electrolytes when dissolved in water decay (dissociated) on ions - positive and negative.

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

3) Dissociation is a reversible process: In parallel with the decay of molecules to ions (dissociation), the process of connecting ions (association) flows.

reversibility

Strong and weak electrolytes.

For the quantitative characteristics of the electrolyte ability to decay on the ions, the concept of the degree of dissociation (α), T . E. The ratio of the number of molecules that have broken into ions, a crucible number of molecules. For example, α \u003d 1 indicates that the electrolyte completely broke up on the ions, and α \u003d 0.2 means that only each fifth of its molecules was preissed. When diluting the concentrated solution, as well as when heated, its electrical conductivity increases, as the degree of dissociation increases.

Depending on the value of α, the electrolytes are conditionally divided into strong (dissonated almost aimed, (α 0.95) of the middle force (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.), almost all salts. The solutions of some mineral acids belong to weak (H 2 S, H 2 SO 3, H 2 CO 3, HCN, HCLO), many organic acids (for example, acetic CH 3 COOH), an aqueous solution of ammonia (NH 3. 2 O), Water, some mercury salts (HGCL 2). The electrolytes of the middle force often refer to the furnace HF, orthophosphorous H 3 PO 4 and nitrogenous HNO 2 acids.

Hydrolysis of salts.

The term "hydrolysis" originated from the Greek words HIDOR (water) and Lysis (decomposition). Under hydrolysis usually understand the exchange reaction between the substance and water. Hydrolytic processes are extremely common in the nature around us (both alive and inanimate), and are also widely used by a person in modern manufacturing and household technologies.

The hydrolysis of salt is called the reaction of the interaction of ions, which are included in the salt, with water, which leads to the formation of a weak electrolyte and is accompanied by a change in the solution medium.

Three types of salts are hydrolysis: three types of salts are subjected:

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

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

NH 4 CL + H 2 O NH 3. H 2 O + HCl

Medium reaction - sour.

b) Salts formed by a strong base and weak acid (K 2 CO 3, Na 2 S - hydrolysis of anion)

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

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

Medium reaction - alkaline.

c) Salts formed by a weak base and weak acid (NH 4) 2 CO 3, Fe 2 (CO 3) 3 - hydrolysis in the cation and anion can occur.

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

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

Often the medium reaction is neutral.

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

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

2Cuso 4 + 2NA 2 CO 3 + H 2 O (Cuoh) 2 CO 3 + 2NA 2 SO 4 + CO 2

When mixing sodium sulfide solutions and aluminum chloride hydrolysis also goes to the end:

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.

Electrolytes.- substances, solutions or melts of which are carried out electrical out.

Neelectrics- Substances, solutions or melts of which do not conduct an electric current.

Dissociation - decay of connections to ions.

The degree of dissociation - The ratio of the number of molecules substantiated on the iones to the total number of molecules in the solution.

Strong electrolytes When dissolved in water, almost completely dissociated on ions.

When writing the dissociation equations of strong electrolytes put a sign of equality.

Strong electrolytes include:

· Salt salts ( see solubility table);

· Many inorganic acids: HNO 3, H 2 SO 4, HCLO 3, HCLO 4, HMNO 4, HCl, HBr, Hi ( look acid-strong electrolytes in solubility table);

· Alkaline, NaOH, KOH bases and alkaline earth (Ca (OH) 2, SR (OH) 2, Ba (OH) 2) metals ( see the base-strong electrolytes in the solubility table).

Weak electrolytes In aqueous solutions, only partially (reversibly) is dissociated by ions.

When writing the dissociation equations of weak electrolytes, the sign of reversibility.

Weak electrolytes include:

· Almost all organic acids and water (H 2 O);

· Some inorganic acids: H 2 S, H 3 PO 4, HCLO 4, H 2 CO 3, HNO 2, H 2 SiO 3 ( look acid-weak electrolytes in solubility table);

· Insoluble metals hydroxides (Mg (OH) 2, Fe (OH) 2, Zn (OH) 2) ( see the foundationc.laboous electrolytes in solubility table).

A number of factors affect the degree of electrolytic dissociation:

the nature of the solvent I. electrolyte: strong electrolytes are substances with ion and covalent high-polar bonds; good ionizing ability, i.e. the ability to cause dissociation of substances, solvents with a large dielectric constant, whose molecules are polar (for example, water);

temperature: Since dissociation is an endothermic process, an increase in temperature increases the value of α;

concentration: when the solution is diluted, the degree of dissociation increases, and with an increase in concentration - decreases;

stage of the dissociation process: Each subsequent stage is less effective than the previous one, about 1000-10,000 times; For example, for phosphoric acid α 1\u003e α 2\u003e α 3:

H3PO4⇄N ++ H2PO-4 (first stage, α 1),

H2PO-4⇄N ++ HPO2-4 (second stage, α 2),

NPO2-4⇄n ++ PO3-4 (third stage, α 3).

For this reason, in the solution of a given acid, the concentration of hydrogen ions is the largest, and phosphate ions RO3-4 is the smallest.

1. The solubility and the degree of dissociation of the substance among themselves are not related. For example, a weak electrolyte is good (unlimited) acetic acid soluble in water.

2. In the solution of weak electrolyte, less than others contain those ions that are formed at the last stage of electrolytic dissociation.

The degree of electrolytic dissociation also affects adding other electrolytes: for example, the degree of dissociation of formic acid

HCOOH ⇄ HCOO - + H +

it decreases if a little sodium formate is added to the solution. This salt dissociates with the formation of HCOO ions formation -:

HCOONA → HCOO - + Na +

As a result, in the solution, the concentration of ions nsoo- increases, and according to the principle of le chateel, an increase in the concentration of formate ions shifts the equilibrium of the formic acid dissociation process to the left, i.e. The degree of dissociation is reduced.

Law of Ostvald Dilution - The ratio, expressing the dependence of the equivalent electrical conductivity of a structural solution of binary weak electrolyte from the concentration of the solution:

Here is the constant of the electrolyte dissociation, the concentration, and the values \u200b\u200bof the equivalent electrical conductivity at a concentration and with infinite dilution, respectively. The ratio is a consequence of the law of existing masses and equality

where is the degree of dissociation.

The law of dilution of ostelalda was led by V. Super in 1888 and it was also confirmed by an experienced way. Experimental establishment of the correctness of the ostel dilution law was of great importance to substantiate the theory of electrolytic dissociation.

Electrolytic water dissociation. The hydrogen pH water indicator is a weak amphoteric electrolyte: H2O H + + OR or, more accurately: 2N2O \u003d H3O + + dissociation of water dissociation at 25 ° C.: Such a constant value corresponds to the dissociation of one of the hundred million water molecules, therefore water concentration Can be considered a constant and equal to 55.55 mol / l (water density 1000 g / l, mass 1 l 1000 g, amount of water of water 1000g: 18g / mol \u003d 55.55 mol, C \u003d 55.55 mol: 1 l \u003d 55 , 55 mol / l). Then this value is permanent at a given temperature (25 ° C), it is called the ionic product of water KW: the dissociation of water is the endothermic process, therefore, with an increase in temperature in accordance with the principle of lessel, dissociation is enhanced, the ionic product increases and reaches at 100 ° C 10-13. In clean water at a 25 ° C of the concentration of hydrogen ions and the hydroxyl are equal to each other: \u003d \u003d 10-7 mol / l solutions in which the concentration of hydrogen ions and hydroxyl are equal to each other are called neutral. If the acid is added to clean water, the concentration of hydrogen ions will increase and becomes greater than 10-7 mol / l, the medium will become acidic, while the concentration of hydroxyl ions will instantly change so that the ionic product of water saves its value 10-14. The same will happen when adding alkali to clean water. The concentrations of hydrogen and hydroxyl ions are interconnected through an ionic product, therefore, knowing the concentration of one of the ions, it is easy to calculate the concentration of the other. For example, if \u003d 10-3 mol / l, then \u003d kw / \u003d 10-14 / 10-3 \u003d 10-11 mol / l, or, if \u003d 10-2 mol / l, then \u003d kw / \u003d 10-14 / 10-2 \u003d 10-12 mol / l. Thus, the concentration of hydrogen ions or hydroxyl can serve as a quantitative characteristic of the acidity or alkalinity of the medium. In practice, they do not use the concentrations of hydrogen ions or hydroxyl, but hydrogen pH or hydroxyl Ron with indicators. The hydrogen indicator pH is equal to a negative decimal logarithm of hydrogen ions concentration: pH \u003d - Lg hydroxyl Ron indicator is equal to a negative decimal logarithm of the hydroxyl ion concentration: Ron \u003d - LG is easy to show, progriforming the ionic product of water, which pH + Ron \u003d 14 if the pH of the medium is 7 - The medium is neutral, if less than 7 is acidic, and the smaller the pH, the higher the concentration of hydrogen ions. Pn is greater than 7 is alkaline medium, the larger pH, the higher the concentration of hydroxyl ions.