Strong electrolytes are dissociated in solution. Electrolytic dissociation: equation, degree, constant, reaction. Classical equilibrium process constant

It has long been known that some solutions carry out electric current (such solutions were called electrolyte), and some are not carried out ( neelectrics).

In addition to electrical conductivity, electrolytes and non-electrolytes have many other differences. With the same molar concentration of electrolyte (compared to non-electrolyites) possess:

• higher boiling point;
• lower freezing temperature;
• higher osmotic pressure;
• lower pair pressure of the solvent.

Such a big difference in the properties of solutions scientists explain the fact that in the electrolytes, during dissolution, a much larger number of particles are formed, which also possess the charge, although, in general, the electrolyte solution is neutral.

For the first time the theory electrolytic dissociation (separation) formulated in 1887 Swedish scientist S. Arrhenius, its main provisions were as follows:

• electrolytes, dissolving in water, dissociate (disintegrate) on positive (cations) and negative (anions) charged ions;
• under the influence of the external electric field, the cations in the electrolyte solution will begin to move to the cathode (negative electrode), anions to the anode (positive electrode);
• electrolytic dissociation is a reversible process - in parallel with the collapse of molecules on the ion goes reverse process Associations (ions are connected in molecules), as a result of which a dynamic equilibrium is established in the solution.

A few years later, in 1891, the Russian scientist I. Heads made significant refinements to the theory of Arrhenius, introducing the concept solvation cations and anions (formation chemical ties Between solvent and soluble substance).

Ions Called atoms (groups of atoms), which have a charge (positive - anions or negative - cations).

Ions are:

• simple - Na +, Mg 2+, S 2-, Cl -
• complex - NO 3 -, NH 4 +, SO 4 2-, PO 4 3-

Mechanism of electrolytic dissociation

The electrolytes are two species: a solution with ion bond and a solution with a covalent bond.

Solvents in which the dissociation process proceeds must consist of polar molecules.

The mechanism of the dissociation of electrolytes with ion and covalent bond is differ.

Sodium chloride is a substance with ion bond, sodium and chlorine ions are located in the nodes of the crystal lattice NaCl.

Fig. 1. Crystal sodium chloride grille.

With immersion crash salt In the first stage of dissolution (dissociation NaCl), polar water molecules under the action of electrostatic attraction are glued with its negative side to sodium cations (Na +), and positive side To chlorine anions (CL -):

Fig. 2 Attraction of polar water molecules to NaCl ions.

As water molecules are glueding with sodium and chlorine ions, the Na + ionic bonds is weakened with Cl -:

The crystal lattice is gradually collapsed, as a result of which the released ions are transferred to the solution in which they immediately bind to water molecules - such ions are called hydrated.

Fig. 3 Weakening of ionic ties of sodium chloride.

Sodium chloride ionic connections and hydrated ions are transferred to the solution:

Fig. 4 Transition of hydrated sodium and chlorine ions into the solution.

IN aqueous solution dissociation of ion connections always flowing completely.

Dissociation of chloroodorod

The chloride is a substance with a covalent polar bond.

Under the influence of water molecules, covalent bonds are polarized even more and become ionic connections, after which the process described above occurs:

Fig. 5 dissociation of the HCl polar molecule.

From the foregoing, it can be concluded that the electrolytic dissociation is possible in polar solvents (water, ethyl alcohol). During dissociation, primarily the most polar bonds (the greatest difference in the electronegativity of atoms components of the connection; see the concept of electronegativity).

The solvent does not only perform the role of the separation of cations and anions of the soluble substance, but also slows down the reverse process of the ion association to the original molecule, since the solvated (hydrated) ions are surrounded by the solvent molecules, which interferes with rapprochement (under the influence of Coulomb electrostatic attraction) and reunification in the molecule Cations and anions. The number of solvent molecules, which are in the hydrated shell of ions, depends on the nature of the ions, concentration and temperature of the solution.

One of the main differences between the dissociation of electrolytes with the polar bond from the discociation of electrolytes with ion bond is that such a dissociation can be partial - it depends on the polarity of links in electrolyte molecules.

The electrolytic dissociation equations are written as follows:

NaCl ↔ Na + + Cl - HCl ↔ H + + Cl -

The electrolytic dissociation occurs due to the energy separated in the process of destruction of the crystal lattice of the soluble substance during the interaction of the solvent molecules with the substance. It should be said that dissociation can occur without a solvent, for example, high temperaturesWhen the melt of the substance is formed (the energy for the destruction of the crystal lattice is taken from the external source of high temperature).

Outcome: Electrolytic dissociation is the process of decay of the substance (electrolyte) on ions (In solvents under the influence of the polar solvent molecules; in melts - under the influence of high temperature).

Properties of ions

Atoms of elements and their ions are far from "relatives". In its physical and chemical properties The ions differ greatly from neutral atoms from which they were formed.

For example, sodium atoms are actively intertwined with water, and sodium anions do not interact with water. Chlorine in a free state is a poisonous gas of yellow-green color, and chloride ions are not poisonous, there are no smell and colors. P\u003e

Such strong differences between atoms and their ions are explained by different electronic structure.

If there are several electrolyte in a solution, they dissociate in the direction of education: 1) precipitation; 2) gases; 3) weak electrolytes.

• example of dissociation with precipitation: BACL 2 + Na 2 SO 4 \u003d Baso 4 ↓ + 2NACL BA 2+ + 2CL - + 2NA + + SO 4 2- \u003d Baso 4 ↓ + 2NA + + 2CL - 2CL - and 2NA + can be reduced Abbreviated ion equation: Ba 2+ + SO 4 2- \u003d Baso 4 ↓
• an example of dissociation to form gases: Caco 3 + 2HCl \u003d CaCl 2 + CO 2 + H 2 O Abbreviated ionic equation: Caco 3 + 2H + \u003d Ca 2+ + CO 2 + H 2 O
• example of dissociation with the formation of weak electrolytes: HCl + NaOH \u003d NaCl + H 2 o Abbreviated ion equation: H + + OH - \u003d H 2 O

You have never thought about why some solutions carry electricity, while others are not? For example, everyone knows that it is better not to take a bath, at the same time laying the hair with a hairdryer. After all, water is a good conductor electric currentAnd if the working hairdryer falls into the water, then not to avoid. In fact, water is not such a good current conductor. There are solutions that carry out electricity is much better. Such substances are called electrolytes. These include acids, alkalis and soluble salt soluble.

Electrolytes - who are they?

The question arises: why solutions of some substances pass electricity, and others - no? It's all about charged particles - cations and anions. When dissolved in water, the electrolytes decompose on ions, which under the action of the electric current move in a given direction. Positively charged cations move to the negative pole - cathode, and negatively charged anions move to a positive pole - anode. The process of decaying a substance on ions when moltening or dissolved in water is a proud name - electrolytic dissociation.

This term introduced a Swedish scientist S.Arrenius into circulation, when he studied the properties of solutions to skip electricity. For this, it closed through a solution of any substance and followed the light bulb lights up or not. If the incandescent light lights up - hence the solution carries out electricity, from which it follows that this substance is an electrolyte. If the bulb remains extinct - then the solution does not carry out electricity, therefore this substance is non-election. Nonethreaches include sugar solutions, alcohol, glucose. But the rants of the table salt, sulfuric acid and perfectly carry out electric current, therefore electrolytic dissociation occurs in them.

How does dissociation proceed?

Subsequently, Russian scientists IA developed and supplemented the theory of electrolytic dissociation. Heads and V.A. Kistyakovsky, applying to her justification, the chemical theory of solutions D.I. Mendeleeva.

These scientists found out that the electrolytic acid dissociation, alkalis and salts proceeds to the hydration of electrolyte, that is, its interactions with water molecules. Ions, cations and anions resulting from this process will be hydrated, that is, associated with water molecules that surround them with a dense ring. Their properties differ significantly from nonhydrated ions.

So, in the solution of nitrate strontium SR (NO3) 2, as well as in cesium hydroxide solutions CSOH, electrolytic dissociation proceeds. Examples of this process can be expressed as follows:

SR (NO3) 2 \u003d SR2 + + 2NO3 -,

those. In the dissociation of one molecule, the strontium is formed by one cation of strontium and 2 nitrate anions;

CSOH \u003d CS + + OH-,

those. During the dissociation of one cesium hydroxide molecule, one cesium cation is formed and one hydroxide anion.

Electrolytic acid dissociation occurs similarly. For iodium acid, this process can be expressed by the following equation:

those. In the dissociation of one molecule of iodium hydrogen acid, one hydrogen cation is formed and one iodine anion.

Dissociation mechanism.

The electrolytic dissociation of electrolyte substances flows into several stages. For substances with ion type of communication, such as NaCl, Naoh This process includes three consecutive process:

initially, water molecules having 2 different poles (positive and negative) and representing a dipole, oriented in crystal ions. The positive pole is attached to the negative crystal ion, and vice versa, a negative pole - to the positive crystal ions;

then there is hydration of crystal ions dipoles of water,

and only after that, hydrated ions, as it were, are diverted in different directions and begin to move in solution or melt it is randomly until they affect the electric field.

For substances with such as HCl and other acids, the dissociation process is similar to, except that initial stage There is a transition covalent Communication In Ion, due to the action of the dipoles of water. These are the main points of the theory of dissociation of substances.

This lesson is devoted to the study of the topic "Electrolytic Dissociation". In the process of studying this topic, you will understand the essence of some amazing facts: why solutions of acids, salts and alkalis are carried out electric current; Why the boiling point of the electrolyte solution is higher compared with the non-electrolithic solution.

Topic: Chemical Communication.

Lesson:Electrolytic dissociation

The topic of our lesson - " Electrolytic dissociation" We will try to explain some amazing facts:

Why solutions of acids, salts and alkalis are conducted by electric current.

Why the boiling point of the electrolyte solution will always be higher than the boiling point of the solution is not an electrolyte of the same concentration.

Svante Arrhenius

In 1887, Swedish physico chemist Svan Arrhenius, Exploring the electrical conductivity of aqueous solutions, suggested that in such solutions, the substances disintegrate into charged particles - ions that can move to the electrodes - a negatively charged cathode and a positively charged anode.

This is the cause of electric current in solutions. This process Received name electrolytic dissociation (literal translation - splitting, decomposition under the action of electricity). This name also assumes that dissociation occurs under the action of electric current. Further studies have shown that it is not: ions are onlysleeves in the solution and exist in it regardless of whether it passes throughsolution current or not.For active participation Svante Arrhenius was formulated by the theory of electrolytic dissociation, which is often called in honor of this scientist. The main idea of \u200b\u200bthis theory is that the electrolytes under the action of the solvent spontaneously disintegrate into ions. And it is these ions that are charge carriers and are responsible for the electrical conductivity of the solution.

Electric current is the directional motion of free charged particles. You already know that solutions and melts of salts and alkalis electrically conductive, Since they are not neutral molecules, but from charged particles - ions. When melting or dissolving ions become freeelectric charge carriers.

The decay process of the substance on free ions during its dissolution or melting is called electrolytic dissociation.

Fig. 1. The decay scheme on sodium chloride ions

The essence of electrolytic dissociation is that ions become free under the influence of water molecule. Fig.1. The process of decay of electrolyte per ions is displayed using a chemical equation. We write the dissociation equation of sodium chloride and calcium bromide. In the dissociation of one praying sodium chloride, one mole of sodium cations and one mole of chloride - anions are formed. NaCl.⇄ Na. + + Cl. -

In the dissociation of one praying calcium bromide, one mole of calcium cations and two praying bromide - anions are formed.

CA.Br. 2 ⇄ CA. 2+ + 2 Br. -

Note: since the electronic particle formula is recorded in the left part of the equation, the total charge of ions should be zero.

Output: in the dissociation of salts, metal cations and anions of the acid residue are formed.

Consider the electrolytic dissociation of alkalis. Write the dissociation equation in potassium hydroxide solution and barium hydroxide.

During dissociation of one mole of potassium hydroxide, one mole of potassium cations and one mole of hydroxide anions are formed. Koh.⇄ K. + + Oh. -

In the dissociation of one praying of the barium hydroxide, one mole of barium cations and two piles of hydroxide - anions are formed. BA.(Oh.) 2 ⇄ BA. 2+ + 2 Oh. -

Output:with electrolytic dissociation, alkalis are formed by metal cations and hydroxide - anions.

Insoluble foundations practically do not expose electrolytic dissociationSince in water they are practically insoluble, and when heated is decomposed, so the melt can not be obtained.

Fig. 2. The structure of chloride and water molecules

Consider the process of electrolytic acid dissociation. Acid molecules are formed by a covalent polar bond, and therefore acids consist not from ions, but from molecules.

The question arises - how then dissociates acid, that is, how free charged particles are formed in acids? It turns out, the ions are formed in acid solutions when dissolved.

Consider the process of electrolytic dissociation of chloroodor in waterBut for this we write down the structure of the molecules of chloroodor and water. Fig.2.

Both molecules are formed by a covalent polar bond. The electron density in the chloride molecule is shifted to the chlorine atom, and in the water molecule - to the oxygen atom. The water molecule is capable of tearing the hydrogen cation from the chloride molecule, while the hydroxony cation is formed H 3 O +.

In the electrolytic dissociation reaction equation, the hydroxonium cation formation is not always taken into account - usually they say that the hydrogen cation is formed.

Then the equation of the dissociation of chloroodor looks like this:

HCL⇄ H. + + Cl. -

In the dissociation of one praying of chloride, one mole of hydrogen cation and one mole chloride - anions are formed.

Speed \u200b\u200bdissociation of sulfuric acid

Consider the process of electrolytic dissociation of sulfuric acid. Sulfuric acid dissociates stepped in two stages.

I.- I stage dissociation

In the first stage one cation of hydrogen is broken and hydrosulfate anion is formed.

II - I'm a stage of dissociation

In the second stage, further dissociation of hydrosulfate - anions occurs. HSO. 4 - ⇄ H. + + SO. 4 2-

This stage is reversible, that is, the sulfate formed - ions can attach the hydrogen cations and turn into hydrosulfate - anions. This is shown a sign of reversibility.

There are acids that are not completely dissociated in the first stage - such acids are weak. For example, coalic acid H 2 CO 3.

Now we can explain why the boiling point of the electrolyte solution will be higher than the boiling point of the non-electrolyte solution.

When dissolved, the solute molecule interacts with the solvent molecules, for example - water. The larger particles of the dissolved substance located in one volume of water, it will be above its boiling point. Now imagine that equal amounts of substance-electrolyte and substances are dissolved in the same volumes of water - non-electrolyte. The electrolyte in water will campack on the ions, and therefore the number of its particles will be greater than in the case of dissolving non-electrolyte. Thus, the presence of free particles in the electrolyte explains why the boiling point of the electrolyte solution will be higher than the boiling point of the non-electrolyte solution.

Summing up lesson

In this lesson, you learned that solutions of acids, salts and alkali electrically conductive, since the charged particles are formed during their dissolution - ions. Such a process is called electrolytic dissociation. During dissociation of salts, metal cations and anions of acid residues are formed. With alkalis dissociation, metal cations and hydroxide anions are formed. During dissociation of acids, hydrogen cations and anions of the acid residue are formed.

1. Rudzitis G.E. Inorganic I. organic chemistry. Grade 9: Tutorial for general educational institutions: Basic level / G. E. Rudzitis, F.G. Feldman. M.: Enlightenment. 2009119s.: Il.

2. Popel P.P. Chimiya: 8 CL: Textbook for general educational institutions / PP. Popel, hp skill. -K.: IC "Academy", 2008.-240 s.: Il.

3. Gabrielyan O.S. Chemistry. Grade 9. Textbook. Publisher: Drop .: 2001. 224c.

1. №№ 1.2 6 (p.13) Rudzitis G.E. Inorganic and organic chemistry. Grade 9: Textbook for general education institutions: Basic level / G. E. Rudzitis, F.G. Feldman. M.: Enlightenment. 2009119s.: Il.

2. What is electrolytic dissociation? Substances, what classes are electrolyte?

3. Substances with which type of communication are electrolytes?

The dissolution of any substance in water is accompanied by the formation of hydrates. If, in this case, there are no formula changes in the particles of the dissolved substance, then such substances belong to neelectrics. They are, for example, gas nitrogen N 2, liquid chloroformCHCl 3, solid sakharesC 12 H 22 O 11, which in aqueous solution exist in the form of hydrates of these molecules.
There are many substances (in general MA), which, after dissolving in water and the formation of hydrates, NH 2 O molecules undergo significant formula changes. As a result, hydrated ions appear in the solution - cations M + * NH 2 O and Anions A * NH 2 O:
Ma * NH 2 O → M + * NH 2 O + A - * NH 2 O
Such substances relate to electrolytes.
The process of appearance of hydrated ions in aqueous solutioncalled electrolytic dissociation (S. Arrhenius 1887).
Electrolytic dissociation of ion crystalline substances (M +) (A -) in water is irreversiblereaction:
(M +) (A -) (T) → (M +) (A -) (P) \u003d (M +) (P) + (A -) (P)
Such substances relate to strong electrolitamThey are many bases and salts, for example:

NaOH \u003d Na + + OH - K 2 SO 4 \u003d 2K + + SO 4 -
Ba (OH) 2 \u003d Ba 2+ + 2OH - Na 2 \u003d 2NA + + S 2-
Electrolytic dissociation of substance Ma consisting of polarcovalent molecules is reversible reaction:
(M-a) (r, w, t) → (M -) (P) ↔ M + (P) A - (P)
Such substances relate to weak electrolytes, they are many acids and some foundations, for example:
a) HNO 2 ↔ H + + NO 2-
b) CH 3 COOH ↔ H + + CH 3 COO -
c) H 2 CO 3 ↔ H + + HCO 3 - (first stage)
HCO 3 - ↔ H + + CO 3 2- (second stage)
d) NH 3 * H 2 O ↔ NH 4 + OH -
In dilute aqueous solutions of weak electrolytes, we will always find both the source molecules and the products of their dissociation are hydrated ions.
The qualitative characteristic of the discociation of electrolytes is called the degree of dissociation and is denoted by ɑ 1, always ɑ\u003e 0.
For strong electrolytes ɑ \u003d 1 by definition (the dissociation of such electrolytes is complete).
For weak Electrolyte the degree of dissociation is the ratio of the painting concentration of the substance predissative (C) to the total concentration of the substance in solution (c):

The degree of dissociation is the share of a unit from 100%. For weak electrolytes ɑ ˂ C 1 (100%). For weak Acids H n A The degree of dissociation for each next stage sharply decreases compared to the previous one:
H 3 PO 4 ↔ H + + H 2 PO 4 - \u003d 23.5%
H 2 PO 4 - ↔ H + + HPO 4 2- \u003d 3 * 10 -4%
HPO 4 2- ↔ H + + PO 4 3- \u003d 2 * 10 -9%
The degree of dissociation depends on the nature and concentration of electrolyte, as well as on the temperature of the solution; It grows as reduction concentration of substance in solution (i.e., when diluting the solution) at heating.
IN diluted solutions strong acids H n A their hydrotions H n -1 A do not exist, for example:
H 2 SO 4 \u003d H + + (1 → 1)
\u003d H + + SO 4 -2 (1 → 1)
As a result: H 2 SO 4 (RSC) \u003d 2H + + SO 4 -2
in concentrated solutions The content of hydroanions (and even the source molecules) becomes noticeable:
H 2 SO 4 - (conc.) ↔ H + + HSO 4 - (1 ˂ 1)
HSO 4 - ↔ H + + SO 4 2- (2 ˂ 1 ˂ 1)
(summarizing the equations of stages of reversible dissociation is impossible!). When heated, the value of 1 and 2 increases, which contributes to the flow of reactions involving concentrated acids.
Acids are electrolytes, which in dissociation supply hydrogen cations in aqueous solution and no other positive anions are formed:
* The letter indicates the degree of flow of any reversible reactions, including the degree of hydrolysis.
H 2 SO 4 \u003d 2H + \u003d SO 4 2-, HF ↔ H + + F -
Common strong acids:
Oxygen-containing acids

Heavyless acids
HCl, HBR, HI, HNCS
In the dilute aqueous solution (conditionally up to 10% or 0.1-molar), these acids are dissociated completely. For strong acids H n A on the list they entered them hydrotions(anions of acidic salts), also dissociate completely under these conditions.
Common weak acids:
Oxygen-containing acids

Heavyless acids
The base is electrolytes, which during dissociation supply hydroxide ions into aqueous solution and no other negative ions are formed:
Koh \u003d K + + Oh -, Ca (OH) 2 \u003d Ca 2+ + 2OH -
Dissociation low-soluble The bases of Mg (OH) 2, Cu (OH) 2, Mn (OH) 2, FE (OH) 2 and other practical significance does not have.
TO stronggrounds ( alkalis) include NaOH, Koh, Ba (OH) 2 some others. The most famous weak base is the ammonia hydrate NH 3 H 2 O.
Middle salts are electrolytes, which, during dissociation, supply any cations, except in the aqueous solution.H. + , and any anions exceptOh.:
Cu (NO 3) 2 \u003d Cu 2+ + 2NO 3 -
Al 2 (SO 4) 3 \u003d 2AL 3+ + 3SO 4 2-
Na (CH 3 COO) \u003d Na + + CH 3 Coo -
BACL 2 \u003d BA 2+ + 2CL
K 2 s \u003d 2k + + s 2-
Mg (CN) 2 \u003d MG 2+ + 2CN -
We are talking not only about well-soluble salts. Dissociation low-solubleand practically Insolublesalts do not matter.
Similarly dissociate Double salts:
Kal (SO 4) 2 \u003d k + + Al 3+ + 2SO 4 2-
Fe (NH 4) 2 (SO 4) 2 \u003d Fe 2+ + 2NH 4 + 2SO 4 2-
Sour salts(Most of them are soluble in water) dissociate completely by the type of medium salts:
KHSO 4 \u003d K + + HSO 4 -
KHCR 2 O 7 \u003d K + + HCR 2 O 7 -
KH 2 PO 4 \u003d K + + H 2 PO 4 -
NaHCO 3 \u003d Na + + HCO 3 -
The formed hydroanions are subjected to, in turn, water exposure:
a) if the hydroanion belongs strong acid, then he will also dissociate completely:
HSO 4 - \u003d H + + HSO 4 2-, HCR 2 O 7 - \u003d H + + CR 2 O 7 2-
And the complete dissociation reaction equation is recorded as:
KHSO 4 \u003d K + + H + + SO 4 2-
KHCR 2 O 7 \u003d K + + H + CR 2 O 7 2-
(solutions of these salts will necessarily be acidic, as well as solutions of the corresponding acids);
b) if the hydrotion belongs to weak acid, then its behavior in water is a double or incomocial dissociation by the type of weak acid:
H 2 PO 4 - ↔ H + + HPO 4 2- (1)
HCO 3 - ↔ H + CO 3 2- (1)

Or interaction with water (called reversible hydrolysis):
H 2 PO 4 - + H 2 O ↔ H 3 PO 4 + OH - (2)
HCO 3 - + H 2 O ↔ H 2 CO 3 + OH - (2)
At 1 2, dissociation prevails (and the solution will be acidic), and at 1 2 - hydrolysis (and the salt solution is alkaline). So, acids will be salts with salts with HSO 3 -, H 2 PO 4 -, H 2 ASO 4 - and HSEO 3 anions, solutions of salts with other anions (most of them) will be alkaline. In other words, the name "sour" for salts with most of the hydroanions does not assume that these anions will behave in the solution as acid (hydrolysis of the hydroanions and the calculation of the relationship between 1 and 2 are studied only in higher School)

MaintenancemgCl (OH), CUCO 3 (OH) 2 salts and others are practically insoluble in the water, and it is impossible to discuss their behavior in aqueous solution.

Theory of electrolytic dissociation Offered a Swedish scientist S. Arrhenius in 1887.

Electrolytic dissociation - This is the decay of electrolyte molecules to form in a solution of positively charged (cation) and negatively charged (anions) ions.

For example, acetic acid dissociates so in an aqueous solution:

CH 3 COOH⇄H + + CH 3 COO -.

Dissociation refer to reversible processes. But different electrolytes dissociate differently. The degree depends on the nature of the electrolyte, its concentration, the nature of the solvent, external conditions (temperature, pressure).

The degree of dissociation α - The ratio of the number of molecules that have broken into ions to the total number of molecules:

α \u003d v'(x) / v (x).

The degree may vary from 0 to 1 (from the lack of dissociation before its complete completion). Denotes in percent. Determined by an experimental way. When the electrolyte dissociation there is an increase in the number of particles in the solution. The dissociation degree shows the power of the electrolyte.

Distinguish strongand Weak electrolytes.

Strong electrolytes - These are electrolytes, the degree of dissociation of which exceeds 30%.

High power electrolytes - These are the degree of dissociation of which divides from 3% to 30%.

Weak electrolytes - The degree of dissociation in aqueous 0.1 M solution is less than 3%.

Examples of weak and strong electrolytes.

Strong electrolytes in dilute solutions aimed at ions, i.e. α \u003d 1. But experiments show that dissociation cannot be equal to 1, it has an approximate value, but not equal to 1. It is not true dissociation, but apparent.

For example, let some connect α \u003d 0.7. Those. According to the theory of Arrhenius in the solution "floats" 30% of the uncommoning molecules. And 70% formed free ions. And the electric status theory gives another definition of this concept: if α \u003d 0.7, then all molecules are dissociated by ions, but the ions are free only by 70%, and the remaining 30% are connected by electrostatic interactions.

The seeming degree of dissociation.

The degree of dissociation depends not only on the nature of the solvent and the soluble substance, but also on the concentration of the solution and temperature.

The dissociation equation can be represented as follows:

AK ⇄ A- + K +.

And the degree of dissociation can be expressed as:

With an increase in the concentration of the solution, the degree of dissociation of electrolyte falls. Those. The values \u200b\u200bof the degree for a particular electrolyte is not a permanent value.

Since dissociation is a reversible process, the reaction rates equations can be written as follows:

If dissociation is equilibrium, then the speed is equal and as a result we get equilibrium constant(Dissociation constant):

K depends on the nature of the solvent and on temperature, but does not depend on the concentration of solutions. It can be seen from the equation that the more unfounded molecules, the less the magnitude of the electrolyte dissociation constant.

Striped acids The stepwise dissociate, and each stage has its own value of the dissociation constant.

If multiple acid dissociates, the first proton is easier to be cleaned, and with an increase in the charge of anion, the attraction increases, and therefore the proton is much more complicated. For example,

The constants of the orthophosphoric acid dissociation at each stage should vary greatly:

I - Stage:

II - Stage:

III - Stage:

At the first stage of orthophosphoric acid - the acid of the middle force, and the 2nd is weak, on the 3rd - very weak.

Examples of equilibrium constants for some electrolyte solutions.

Consider an example:

If the solution in which silver is contained to make metal copper, then at the time of equilibrium, the concentration of copper ions should be greater than the silver concentration.

But the constant has a low value:

AgCl⇄Ag + + Cl -.

What does very little silver chloride have dissolved by the time of the equilibrium.

The concentration of metallic copper and silver was introduced into the equilibrium constant.

Ionic product of water.

The table has data:

This constant is called by ionic waterwhich depends only on temperature. According to the dissociation by 1 ion H + accounts for one hydroxide ion. In clear water, the concentration of these ions is the same: [ H. + ] = [Oh. - ].

From here, [ H. + ] = [Oh. -] \u003d \u003d 10-7 mol / l.

If you add a foreign substance, for example, hydrogen chloride acid, then the concentration of hydrogen ions will increase, but the ionic product of water from the concentration does not depend.

And if adding alkali, the concentration of ions will increase, and the amount of hydrogen decreases.

Concentration and interrelated: the more one value, the smaller the other.

The acidity of the solution (pH).

Acidness of solutions is usually expressed by the concentration of ions H +. In acidic environments pH<10 -7 моль/л, в нейтральных - pH \u003d 10 -7 mol / l, in alkaline - RN.\u003e 10 -7 mol / l.
The acidity of the solution is expressed through the negative logarithm of the concentration of hydrogen ions, calling it pH.

pH \u003d -lG[ H. + ].

The relationship between the constant and the degree of dissociation.

Consider an example of acetic acid dissociation:

We find a constant:

Molar concentration C \u003d 1 /V., We substitute to the equation and get:

These equations are broadcast Law V. OstvaldaAccording to which the constant of the electrolyte dissociation does not depend on the dilution of the crop.