Alkali metal hydroxides - under normal conditions, they are solid white crystalline substances, hygroscopic, soapy to the touch, very soluble in water (their dissolution is an exothermic process), fusible. Hydroxides of alkaline earth metals Ca (OH) 2, Sr (OH) 2, Ba (OH) 2) are white powdery substances, much less soluble in water compared to alkali metal hydroxides. Water-insoluble bases usually form as gel-like precipitates that decompose on storage. For example, Cu (OH) 2 is a blue gelatinous precipitate.

3.1.4 Chemical properties of bases.

The properties of bases are due to the presence of OH - ions. There are differences in the properties of alkalis and water-insoluble bases, but the common property is the reaction of interaction with acids. The chemical properties of the bases are presented in table 6.

Table 6 - Chemical properties of bases

alkalis	Insoluble bases
All bases react with acids ( neutralization reaction)
2NaOH + H 2 SO 4 \u003d Na 2 SO 4 + 2H 2 O	Cr(OH) 2 + 2HC1 = CrC1 2 + 2H 2 O
Bases react with acidic oxides with the formation of salt and water: 6KOH + P 2 O 5 \u003d 2K 3 RO 4 + 3H 2 O
Alkalis react with salt solutions if one of the reaction products precipitates out(i.e. if an insoluble compound forms): CuSO 4 + 2KOH \u003d Cu (OH) 2  + K 2 SO 4 Na 2 SO 4 + Ba(OH) 2 = 2NaOH + BaSO 4 	Water-insoluble bases and amphoteric hydroxides decompose when heated to the corresponding oxide and water: Mn (OH) 2  MnO + H 2 O Cu (OH) 2  CuO + H 2 O
Alkalis can be detected with an indicator. In an alkaline environment: litmus - blue, phenolphthalein - raspberry, methyl orange - yellow

3.1.5 Essential foundations.

NaOH- caustic soda, caustic soda. Fusible (t pl = 320 °C) white hygroscopic crystals, highly soluble in water. The solution is soapy to the touch and is a dangerous caustic liquid. NaOH is one of the most important products of the chemical industry. It is required in large quantities for the purification of petroleum products, and is widely used in soap, paper, textile and other industries, as well as for the production of artificial fiber.

KOH- caustic potash. White hygroscopic crystals, highly soluble in water. The solution is soapy to the touch and is a dangerous caustic liquid. The properties of KOH are similar to those of NaOH, but potassium hydroxide is used much less frequently due to its higher cost.

Ca(OH) 2 - slaked lime. White crystals, slightly soluble in water. The solution is called “lime water”, the suspension is called “milk of lime”. Lime water is used to recognize carbon dioxide, it becomes cloudy when CO 2 is passed through. Hydrated lime is widely used in the construction industry as a basis for the manufacture of binders.

Metal and hydroxyl group (OH). For example, sodium hydroxide is NaOH, calcium hydroxide - Ca(Oh) 2 , barium hydroxide - Ba(Oh) 2 etc.

Obtaining hydroxides.

1. Exchange reaction:

CaSO 4 + 2NaOH \u003d Ca (OH) 2 + Na 2 SO 4,

2. Electrolysis of aqueous solutions of salts:

2KCl + 2H 2 O \u003d 2KOH + H 2 + Cl 2,

3. Interaction of alkali and alkaline earth metals or their oxides with water:

K + 2H 2 O = 2 KOH + H 2 ,

Chemical properties of hydroxides.

1. Hydroxides are alkaline in nature.

2. Hydroxides dissolve in water (alkali) and are insoluble. For example, KOH- dissolves in water Ca(Oh) 2 - slightly soluble, has a white solution. Metals of the 1st group of the periodic table D.I. Mendeleev give soluble bases (hydroxides).

3. Hydroxides decompose when heated:

Cu(Oh) 2 = CuO + H 2 O.

4. Alkalis react with acidic and amphoteric oxides:

2KOH + CO 2 \u003d K 2 CO 3 + H 2 O.

5. Alkalis can react with some non-metals at different temperatures in different ways:

NaOH + Cl 2 = NaCl + NaOCl + H 2 O(cold),

NaOH + 3 Cl 2 = 5 NaCl + NaClO 3 + 3 H 2 O(heat).

6. Interact with acids:

KOH + HNO3 = KNO 3 + H 2 O.

Bases, amphoteric hydroxides

Bases are complex substances consisting of metal atoms and one or more hydroxo groups (-OH). The general formula is Me + y (OH) y, where y is the number of hydroxo groups equal to the oxidation state of the metal Me. The table shows the classification of bases.

Properties of alkali hydroxides of alkali and alkaline earth metals

1. Aqueous solutions of alkalis are soapy to the touch, change the color of indicators: litmus - blue, phenolphthalein - raspberry.

2. Aqueous solutions dissociate:

3. Interact with acids, entering into an exchange reaction:

Polyacid bases can give intermediate and basic salts:

4. Interact with acid oxides, forming medium and acid salts, depending on the basicity of the acid corresponding to this oxide:

5. Interact with amphoteric oxides and hydroxides:

a) fusion:

b) in solutions:

6. React with water-soluble salts if a precipitate or gas is formed:

Insoluble bases (Cr (OH) 2, Mn (OH) 2, etc.) interact with acids and decompose when heated:

Amphoteric hydroxides

Compounds are called amphoteric, which, depending on the conditions, can be both donors of hydrogen cations and exhibit acidic properties, and their acceptors, i.e., exhibit basic properties.

Chemical properties of amphoteric compounds

1. Interacting with strong acids, they reveal the main properties:

Zn(OH) 2 + 2HCl = ZnCl 2 + 2H 2 O

2. Interacting with alkalis - strong bases, they exhibit acidic properties:

Zn (OH) 2 + 2NaOH \u003d Na 2 ( complex salt)

Al (OH) 3 + NaOH \u003d Na ( complex salt)

Compounds are called complex in which at least one covalent bond was formed by the donor-acceptor mechanism.

The general method for obtaining bases is based on exchange reactions, by which both insoluble and soluble bases can be obtained.

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

K 2 CO 3 + Ba (OH) 2 \u003d 2 KOH + BaCO 3 ↓

When soluble bases are obtained by this method, an insoluble salt precipitates.

When obtaining water-insoluble bases with amphoteric properties, an excess of alkali should be avoided, since dissolution of the amphoteric base may occur, for example:

AlCl 3 + 4KOH \u003d K [Al (OH) 4] + 3KSl

In such cases, ammonium hydroxide is used to obtain hydroxides, in which amphoteric hydroxides do not dissolve:

AlCl 3 + 3NH 3 + ZH 2 O \u003d Al (OH) 3 ↓ + 3NH 4 Cl

Hydroxides of silver and mercury decompose so easily that when you try to obtain them by an exchange reaction, instead of hydroxides, oxides precipitate:

2AgNO 3 + 2KOH \u003d Ag 2 O ↓ + H 2 O + 2KNO 3

In industry, alkalis are usually obtained by electrolysis of aqueous solutions of chlorides.

2NaCl + 2H 2 O → ϟ → 2NaOH + H 2 + Cl 2

Alkalis can also be obtained by reacting alkali and alkaline earth metals or their oxides with water.

2Li + 2H 2 O \u003d 2LiOH + H 2

SrO + H 2 O \u003d Sr (OH) 2

acids

Acids are called complex substances, the molecules of which consist of hydrogen atoms that can be replaced by metal atoms, and acid residues. Under normal conditions, acids can be solid (phosphoric H 3 PO 4; silicon H 2 SiO 3) and liquid (sulfuric acid H 2 SO 4 will be a pure liquid).

Gases such as hydrogen chloride HCl, hydrogen bromide HBr, hydrogen sulfide H 2 S form the corresponding acids in aqueous solutions. The number of hydrogen ions formed by each acid molecule during dissociation determines the charge of the acid residue (anion) and the basicity of the acid.

According to protolytic theory of acids and bases, proposed simultaneously by the Danish chemist Bronsted and the English chemist Lowry, an acid is a substance splitting off with this reaction protons, a basis- a substance capable of receive protons.

acid → base + H +

Based on these ideas, it is clear basic properties of ammonia, which, due to the presence of a lone electron pair at the nitrogen atom, effectively accepts a proton when interacting with acids, forming an ammonium ion through a donor-acceptor bond.

HNO 3 + NH 3 ⇆ NH 4 + + NO 3 -

acid base acid base

A more general definition of acids and bases proposed by the American chemist G. Lewis. He suggested that acid-base interactions are quite do not necessarily occur with protone transfer. In the determination of acids and bases according to Lewis, the main role in chemical reactions is given to electronic steam.

Cations, anions, or neutral molecules that can accept one or more pairs of electrons are called Lewis acids.

For example, aluminum fluoride AlF 3 is an acid, since it is able to accept an electron pair when interacting with ammonia.

AlF 3 + :NH 3 ⇆ :

Cations, anions or neutral molecules capable of donating electron pairs are called Lewis bases (ammonia is a base).

The Lewis definition covers all acid-base processes that have been considered by the previously proposed theories. The table compares the definitions of acids and bases currently in use.

Nomenclature of acids

Since there are different definitions of acids, their classification and nomenclature are rather arbitrary.

According to the number of hydrogen atoms capable of splitting off in an aqueous solution, acids are divided into monobasic(e.g. HF, HNO 2), dibasic(H 2 CO 3 , H 2 SO 4) and tribasic(H 3 RO 4).

According to the composition of the acid is divided into anoxic(HCl, H 2 S) and oxygen-containing(HClO 4 , HNO 3).

Usually names of oxygenated acids derived from the name of a non-metal with the addition of the endings -kai, -way, if the oxidation state of the non-metal is equal to the group number. As the oxidation state decreases, the suffixes change (in order of decreasing metal oxidation state): - oval, ististaya, - ovate:

If we consider the polarity of the hydrogen-non-metal bond within a period, we can easily relate the polarity of this bond to the position of the element in the Periodic Table. From metal atoms that easily lose valence electrons, hydrogen atoms accept these electrons, forming a stable two-electron shell like the shell of a helium atom, and give ionic metal hydrides.

In hydrogen compounds of elements of groups III-IV of the Periodic system, boron, aluminum, carbon, silicon form covalent, weakly polar bonds with hydrogen atoms that are not prone to dissociation. For elements of groups V-VII of the Periodic system, within a period, the polarity of the non-metal-hydrogen bond increases with the charge of the atom, but the distribution of charges in the resulting dipole is different than in hydrogen compounds of elements that tend to donate electrons. Atoms of non-metals, in which several electrons are needed to complete the electron shell, pull towards themselves (polarize) a pair of bond electrons the stronger, the greater the charge of the nucleus. Therefore, in the series CH 4 - NH 3 - H 2 O - HF or SiH 4 - PH 3 - H 2 S - Hcl, bonds with hydrogen atoms, while remaining covalent, become more polar, and the hydrogen atom in the dipole of the element-hydrogen bond becomes more electropositive. If polar molecules are in a polar solvent, the process of electrolytic dissociation can occur.

Let us discuss the behavior of oxygen-containing acids in aqueous solutions. These acids have an H-O-E bond and, naturally, the O-E bond affects the polarity of the H-O bond. Therefore, these acids dissociate, as a rule, more easily than water.

H 2 SO 3 + H 2 O ⇆ H s O + + HSO 3

HNO 3 + H 2 O ⇆ H s O + + NO 3

Let's look at a few examples properties of oxygenated acids, formed by elements that are capable of exhibiting different oxidation states. It is known that hypochlorous acid HClO very weak hydrochloric acid HClO 2 also weak but stronger than hypochlorous, hypochlorous acid HclO 3 strong. Perchloric acid HClO 4 is one of the the strongest inorganic acids.

Dissociation according to the acidic type (with the elimination of the H ion) requires breaking the O-H bond. How can one explain the decrease in the strength of this bond in the series HClO - HClO 2 - HClO 3 - HClO 4? In this series, the number of oxygen atoms associated with the central chlorine atom increases. Each time a new bond of oxygen with chlorine is formed, an electron density is drawn away from the chlorine atom, and hence from the single O-Cl bond. As a result, the electron density partially leaves the О-Н bond, which is weakened because of this.

Such a pattern - enhancement of acidic properties with an increase in the degree of oxidation of the central atom - characteristic not only for chlorine, but also for other elements. For example, nitric acid HNO 3 , in which the nitrogen oxidation state is +5, is stronger than nitrous acid HNO 2 (nitrogen oxidation state is +3); sulfuric acid H 2 SO 4 (S +6) is stronger than sulfurous acid H 2 SO 3 (S +4).

Obtaining acids

1. Anoxic acids can be obtained in the direct combination of non-metals with hydrogen.

H 2 + Cl 2 → 2HCl,

H 2 + S ⇆ H 2 S

2. Some oxygenated acids can be obtained interaction of acid oxides with water.

3. Both anoxic and oxygenated acids can be obtained according to exchange reactions between salts and other acids.

BaBr 2 + H 2 SO 4 \u003d BaSO 4 ↓ + 2HBr

CuSO 4 + H 2 S \u003d H 2 SO 4 + CuS ↓

FeS + H 2 SO 4 (pa zb) \u003d H 2 S + FeSO 4

NaCl (T) + H 2 SO 4 (conc) = HCl + NaHSO 4

AgNO 3 + HCl = AgCl↓ + HNO 3

CaCO 3 + 2HBr \u003d CaBr 2 + CO 2 + H 2 O

4. Some acids can be obtained using redox reactions.

H 2 O 2 + SO 2 \u003d H 2 SO 4

3P + 5HNO 3 + 2H 2 O \u003d ZH 3 PO 4 + 5NO 2

Sour taste, action on indicators, electrical conductivity, interaction with metals, basic and amphoteric oxides, bases and salts, formation of esters with alcohols - these properties are common to inorganic and organic acids.

can be divided into two types of reactions:

1) general for acids the reactions are associated with the formation of hydronium ion H 3 O + in aqueous solutions;

2) specific(i.e. characteristic) reactions specific acids.

The hydrogen ion can enter into redox reactions, reducing to hydrogen, as well as in a compound reaction with negatively charged or neutral particles having lone pairs of electrons, i.e. in acid-base reactions.

The general properties of acids include the reactions of acids with metals in the series of voltages up to hydrogen, for example:

Zn + 2Н + = Zn 2+ + Н 2

Acid-base reactions include reactions with basic oxides and bases, as well as with medium, basic, and sometimes acidic salts.

2 CO 3 + 4HBr \u003d 2CuBr 2 + CO 2 + 3H 2 O

Mg (HCO 3) 2 + 2HCl \u003d MgCl 2 + 2CO 2 + 2H 2 O

2KHSO 3 + H 2 SO 4 \u003d K 2 SO 4 + 2SO 2 + 2H 2 O

Note that polybasic acids dissociate stepwise, and at each next step, dissociation is more difficult, therefore, with an excess of acid, acidic salts are most often formed, rather than medium ones.

Ca 3 (PO 4) 2 + 4H 3 PO 4 \u003d 3Ca (H 2 PO 4) 2

Na 2 S + H 3 PO 4 = Na 2 HPO 4 + H 2 S

NaOH + H 3 PO 4 = NaH 2 PO 4 + H 2 O

KOH + H 2 S \u003d KHS + H 2 O

At first glance, the formation of acidic salts may seem surprising. monobasic hydrofluoric (hydrofluoric) acid. However, this fact can be explained. Unlike all other hydrohalic acids, hydrofluoric acid is partially polymerized in solutions (due to the formation of hydrogen bonds) and different particles (HF) X can be present in it, namely H 2 F 2, H 3 F 3, etc.

A special case of acid-base balance - reactions of acids and bases with indicators that change color depending on the acidity of the solution. Indicators are used in qualitative analysis to detect acids and bases in solutions.

The most commonly used indicators are litmus(in neutral environment purple, in sour - red, in alkaline - blue), methyl orange(in sour environment red, in neutral - orange, in alkaline - yellow), phenolphthalein(in strongly alkaline environment crimson red, in neutral and acidic - colorless).

Specific properties different acids can be of two types: first, the reactions leading to the formation insoluble salts, and, secondly, redox transformations. If the reactions associated with the presence of an H + ion in them are common to all acids (qualitative reactions for detecting acids), specific reactions are used as qualitative reactions for individual acids:

Ag + + Cl - = AgCl (white precipitate)

Ba 2+ + SO 4 2- \u003d BaSO 4 (white precipitate)

3Ag + + PO 4 3 - = Ag 3 PO 4 (yellow precipitate)

Some specific reactions of acids are due to their redox properties.

Anoxic acids in aqueous solution can only oxidize.

2KMnO 4 + 16HCl \u003d 5Cl 2 + 2KCl + 2MnCl 2 + 8H 2 O

H 2 S + Br 2 \u003d S + 2HBg

Oxygen-containing acids can only be oxidized if the central atom in them is in a lower or intermediate oxidation state, as, for example, in sulfurous acid:

H 2 SO 3 + Cl 2 + H 2 O \u003d H 2 SO 4 + 2HCl

Many oxygen-containing acids, in which the central atom has the maximum oxidation state (S +6, N +5, Cr +6), exhibit the properties of strong oxidizing agents. Concentrated H 2 SO 4 is a strong oxidizing agent.

Cu + 2H 2 SO 4 (conc) = CuSO 4 + SO 2 + 2H 2 O

Pb + 4HNO 3 \u003d Pb (NO 3) 2 + 2NO 2 + 2H 2 O

C + 2H 2 SO 4 (conc) = CO 2 + 2SO 2 + 2H 2 O

It should be remembered that:

• Acid solutions react with metals that are in the electrochemical series of voltages to the left of hydrogen, subject to a number of conditions, the most important of which is the formation of a soluble salt as a result of the reaction. The interaction of HNO 3 and H 2 SO 4 (conc.) with metals proceeds differently.

Concentrated sulfuric acid in the cold passivates aluminum, iron, chromium.

• In water, acids dissociate into hydrogen cations and anions of acid residues, for example:

• Inorganic and organic acids interact with basic and amphoteric oxides, provided that a soluble salt is formed:

• Both those and other acids react with bases. Polybasic acids can form both medium and acidic salts (these are neutralization reactions):

• The reaction between acids and salts occurs only if a precipitate or gas is formed:

The interaction of H 3 PO 4 with limestone will stop due to the formation of the last insoluble precipitate Ca 3 (PO 4) 2 on the surface.

The features of the properties of nitric HNO 3 and concentrated sulfuric H 2 SO 4 (conc.) acids are due to the fact that when they interact with simple substances (metals and non-metals), not H + cations, but nitrate and sulfate ions will act as oxidizing agents. It is logical to expect that as a result of such reactions, not hydrogen H 2 is formed, but other substances are obtained: necessarily salt and water, as well as one of the products of the reduction of nitrate or sulfate ions, depending on the concentration of acids, the position of the metal in a series of voltages and reaction conditions (temperature, metal fineness, etc.).

These features of the chemical behavior of HNO 3 and H 2 SO 4 (conc.) clearly illustrate the thesis of the theory of chemical structure about the mutual influence of atoms in the molecules of substances.

The concepts of volatility and stability (stability) are often confused. Volatile acids are called acids, the molecules of which easily pass into a gaseous state, that is, they evaporate. For example, hydrochloric acid is a volatile but persistent, stable acid. The volatility of unstable acids cannot be judged. For example, non-volatile, insoluble silicic acid decomposes into water and SiO 2 . Aqueous solutions of hydrochloric, nitric, sulfuric, phosphoric and a number of other acids are colorless. An aqueous solution of chromic acid H 2 CrO 4 is yellow, permanganic acid HMnO 4 is raspberry.

Reference material for passing the test:

periodic table

Solubility table

Foundations – complex substances that consist of a metal cation Me + (or a metal-like cation, for example, an ammonium ion NH 4 +) and a hydroxide anion OH -.

Based on their solubility in water, bases are divided into soluble (alkali) and insoluble bases . Also have unstable grounds that spontaneously decompose.

Getting the grounds

1. Interaction of basic oxides with water. At the same time, they react with water under normal conditions only those oxides that correspond to a soluble base (alkali). Those. this way you can only get alkalis:

basic oxide + water = base

For example , sodium oxide forms in water sodium hydroxide(sodium hydroxide):

Na 2 O + H 2 O → 2NaOH

At the same time about copper(II) oxide With water does not react:

CuO + H 2 O ≠

2. Interaction of metals with water. Wherein react with waterunder normal conditionsonly alkali metals(lithium, sodium, potassium, rubidium, cesium), calcium, strontium and barium.In this case, a redox reaction occurs, hydrogen acts as an oxidizing agent, and a metal acts as a reducing agent.

metal + water = alkali + hydrogen

For example, potassium reacts with water very violent:

2K 0 + 2H 2 + O → 2K + OH + H 2 0

3. Electrolysis of solutions of some alkali metal salts. As a rule, to obtain alkalis, electrolysis is subjected to solutions of salts formed by alkali or alkaline earth metals and anoxic acids (except hydrofluoric) - chlorides, bromides, sulfides, etc. This issue is discussed in more detail in the article .

For example , electrolysis of sodium chloride:

2NaCl + 2H 2 O → 2NaOH + H 2 + Cl 2

4. Bases are formed by the interaction of other alkalis with salts. In this case, only soluble substances interact, and an insoluble salt or an insoluble base should form in the products:

or

lye + salt 1 = salt 2 ↓ + lye

For example: potassium carbonate reacts in solution with calcium hydroxide:

K 2 CO 3 + Ca(OH) 2 → CaCO 3 ↓ + 2KOH

For example: copper (II) chloride reacts in solution with sodium hydroxide. At the same time, it drops blue precipitate of copper(II) hydroxide:

CuCl 2 + 2NaOH → Cu(OH) 2 ↓ + 2NaCl

Chemical properties of insoluble bases

1. Insoluble bases interact with strong acids and their oxides (and some medium acids). At the same time, they form salt and water.

insoluble base + acid = salt + water

insoluble base + acid oxide = salt + water

For example ,copper (II) hydroxide interacts with strong hydrochloric acid:

Cu(OH) 2 + 2HCl = CuCl 2 + 2H 2 O

In this case, copper (II) hydroxide does not interact with acidic oxide weak carbonic acid - carbon dioxide:

Cu(OH) 2 + CO 2 ≠

2. Insoluble bases decompose when heated into oxide and water.

For example, iron (III) hydroxide decomposes into iron (III) oxide and water when calcined:

2Fe(OH) 3 = Fe 2 O 3 + 3H 2 O

3. Insoluble bases do not interactwith amphoteric oxides and hydroxides.

insoluble base + amphoteric oxide ≠

insoluble base + amphoteric hydroxide ≠

4. Some insoluble bases can act asreducing agents. Reducing agents are bases formed by metals with minimum or intermediate oxidation state, which can increase their oxidation state (iron (II) hydroxide, chromium (II) hydroxide, etc.).

For example , iron (II) hydroxide can be oxidized with atmospheric oxygen in the presence of water to iron (III) hydroxide:

4Fe +2 (OH) 2 + O 2 0 + 2H 2 O → 4Fe +3 (O -2 H) 3

Chemical properties of alkalis

1. Alkalis interact with any acids - both strong and weak . In this case, salt and water are formed. These reactions are called neutralization reactions. Possibly education acid salt, if the acid is polybasic, at a certain ratio of reagents, or in excess acid. AT excess alkali average salt and water are formed:

alkali (excess) + acid \u003d medium salt + water

alkali + polybasic acid (excess) = acid salt + water

For example , sodium hydroxide, when interacting with tribasic phosphoric acid, can form 3 types of salts: dihydrophosphates, phosphates or hydrophosphates.

In this case, dihydrophosphates are formed in an excess of acid, or at a molar ratio (the ratio of the amounts of substances) of the reagents 1:1.

NaOH + H 3 PO 4 → NaH 2 PO 4 + H 2 O

With a molar ratio of the amount of alkali and acid of 2: 1, hydrophosphates are formed:

2NaOH + H 3 PO 4 → Na 2 HPO 4 + 2H 2 O

In excess of alkali, or at a molar ratio of alkali and acid of 3:1, an alkali metal phosphate is formed.

3NaOH + H 3 PO 4 → Na 3 PO 4 + 3H 2 O

2. Alkalis interact withamphoteric oxides and hydroxides. Wherein common salts are formed in the melt , a in solution - complex salts .

alkali (melt) + amphoteric oxide = medium salt + water

lye (melt) + amphoteric hydroxide = medium salt + water

alkali (solution) + amphoteric oxide = complex salt

alkali (solution) + amphoteric hydroxide = complex salt

For example , when aluminum hydroxide reacts with sodium hydroxide in the melt sodium aluminate is formed. The more acidic hydroxide forms an acid residue:

NaOH + Al(OH) 3 = NaAlO 2 + 2H 2 O

BUT in solution a complex salt is formed:

NaOH + Al(OH) 3 = Na

Pay attention to how the formula of a complex salt is compiled:first we choose the central atom (toas a rule, it is a metal from amphoteric hydroxide).Then add to it ligands- in our case, these are hydroxide ions. The number of ligands is, as a rule, 2 times greater than the oxidation state of the central atom. But the aluminum complex is an exception, its number of ligands is most often 4. We enclose the resulting fragment in square brackets - this is a complex ion. We determine its charge and add the required number of cations or anions from the outside.

3. Alkalis interact with acidic oxides. It is possible to form sour or medium salt, depending on the molar ratio of alkali and acid oxide. In excess of alkali, an average salt is formed, and in an excess of acidic oxide, an acid salt is formed:

alkali (excess) + acid oxide \u003d medium salt + water

or:

alkali + acid oxide (excess) = acid salt

For example , when interacting excess sodium hydroxide With carbon dioxide, sodium carbonate and water are formed:

2NaOH + CO 2 \u003d Na 2 CO 3 + H 2 O

And when interacting excess carbon dioxide with sodium hydroxide, only sodium bicarbonate is formed:

2NaOH + CO 2 = NaHCO 3

4. Alkalis interact with salts. alkalis react only with soluble salts in solution, provided that products form gas or precipitate . These reactions proceed according to the mechanism ion exchange.

alkali + soluble salt = salt + corresponding hydroxide

Alkalis interact with solutions of metal salts, which correspond to insoluble or unstable hydroxides.

For example, sodium hydroxide interacts with copper sulfate in solution:

Cu 2+ SO 4 2- + 2Na + OH - = Cu 2+ (OH) 2 - ↓ + Na 2 + SO 4 2-

Also alkalis interact with solutions of ammonium salts.

For example , potassium hydroxide interacts with ammonium nitrate solution:

NH 4 + NO 3 - + K + OH - \u003d K + NO 3 - + NH 3 + H 2 O

! When salts of amphoteric metals interact with an excess of alkali, a complex salt is formed!

Let's look at this issue in more detail. If the salt formed by the metal to which amphoteric hydroxide , interacts with a small amount of alkali, then the usual exchange reaction proceeds, and precipitatesthe hydroxide of this metal .

For example , excess zinc sulfate reacts in solution with potassium hydroxide:

ZnSO 4 + 2KOH \u003d Zn (OH) 2 ↓ + K 2 SO 4

However, in this reaction, not a base is formed, but mphoteric hydroxide. And, as we mentioned above, amphoteric hydroxides dissolve in an excess of alkalis to form complex salts . T Thus, during the interaction of zinc sulfate with excess alkali solution a complex salt is formed, no precipitate is formed:

ZnSO 4 + 4KOH \u003d K 2 + K 2 SO 4

Thus, we obtain 2 schemes for the interaction of metal salts, which correspond to amphoteric hydroxides, with alkalis:

amphoteric metal salt (excess) + alkali = amphoteric hydroxide↓ + salt

amph.metal salt + alkali (excess) = complex salt + salt

5. Alkalis interact with acidic salts.In this case, medium salts or less acidic salts are formed.

sour salt + alkali \u003d medium salt + water

For example , Potassium hydrosulfite reacts with potassium hydroxide to form potassium sulfite and water:

KHSO 3 + KOH \u003d K 2 SO 3 + H 2 O

It is very convenient to determine the properties of acid salts by mentally breaking an acid salt into 2 substances - an acid and a salt. For example, we break sodium bicarbonate NaHCO 3 into uric acid H 2 CO 3 and sodium carbonate Na 2 CO 3 . The properties of bicarbonate are largely determined by the properties of carbonic acid and the properties of sodium carbonate.

6. Alkalis interact with metals in solution and melt. In this case, a redox reaction occurs, in the solution complex salt and hydrogen, in the melt - medium salt and hydrogen.

Note! Only those metals react with alkalis in solution, in which the oxide with the minimum positive oxidation state of the metal is amphoteric!

For example , iron does not react with an alkali solution, iron (II) oxide is basic. BUT aluminum dissolves in an aqueous solution of alkali, aluminum oxide is amphoteric:

2Al + 2NaOH + 6H 2 + O = 2Na + 3H 2 0

7. Alkalis interact with non-metals. In this case, redox reactions take place. Usually, non-metals disproportionate in alkalis. do not react with alkalis oxygen, hydrogen, nitrogen, carbon and inert gases (helium, neon, argon, etc.):

NaOH + O 2 ≠

NaOH + N 2 ≠

NaOH+C≠

Sulfur, chlorine, bromine, iodine, phosphorus and other non-metals disproportionate in alkalis (i.e. self-oxidize-self-repair).

For example, chlorinewhen interacting with cold alkali goes into oxidation states -1 and +1:

2NaOH + Cl 2 0 \u003d NaCl - + NaOCl + + H 2 O

Chlorine when interacting with hot lye goes into oxidation states -1 and +5:

6NaOH + Cl 2 0 \u003d 5NaCl - + NaCl + 5 O 3 + 3H 2 O

Silicon oxidized by alkalis to an oxidation state of +4.

For example, in solution:

2NaOH + Si 0 + H 2 + O \u003d NaCl - + Na 2 Si + 4 O 3 + 2H 2 0

Fluorine oxidizes alkalis:

2F 2 0 + 4NaO -2 H \u003d O 2 0 + 4NaF - + 2H 2 O

You can read more about these reactions in the article.

8. Alkalis do not decompose when heated.

The exception is lithium hydroxide:

2LiOH \u003d Li 2 O + H 2 O

1. Bases interact with acids to form salt and water:

Cu(OH) 2 + 2HCl = CuCl 2 + 2H 2 O

2. With acid oxides, forming salt and water:

Ca(OH) 2 + CO 2 = CaCO 3 + H 2 O

3. Alkalis react with amphoteric oxides and hydroxides, forming salt and water:

2NaOH + Cr 2 O 3 \u003d 2NaCrO 2 + H 2 O

KOH + Cr(OH) 3 = KCrO 2 + 2H 2 O

4. Alkalis interact with soluble salts, forming either a weak base, or a precipitate, or a gas:

2NaOH + NiCl 2 \u003d Ni (OH) 2 ¯ + 2NaCl

base

2KOH + (NH 4) 2 SO 4 \u003d 2NH 3 + 2H 2 O + K 2 SO 4

Ba(OH) 2 + Na 2 CO 3 = BaCO 3 ¯ + 2NaOH

5. Alkalis react with some metals, which correspond to amphoteric oxides:

2NaOH + 2Al + 6H 2 O = 2Na + 3H 2

6. The action of alkali on the indicator:

Oh - + phenolphthalein ® raspberry color

Oh - + litmus ® blue color

7. Decomposition of some bases when heated:

Сu(OH) 2 ® CuO + H 2 O

Amphoteric hydroxides- chemical compounds that exhibit the properties of both bases and acids. Amphoteric hydroxides correspond to amphoteric oxides (see section 3.1).

Amphoteric hydroxides are usually written in the form of a base, but they can also be represented as an acid:

Zn(OH) 2 Û H 2 ZnO 2

base to

Chemical properties of amphoteric hydroxides

1. Amphoteric hydroxides interact with acids and acid oxides:

Be(OH) 2 + 2HCl = BeCl 2 + 2H 2 O

Be(OH) 2 + SO 3 = BeSO 4 + H 2 O

2. Interact with alkalis and basic oxides of alkali and alkaline earth metals:

Al(OH) 3 + NaOH = NaAlO 2 + 2H 2 O;

H 3 AlO 3 acid sodium metaaluminate

(H 3 AlO 3 ® HAlO 2 + H 2 O)

2Al(OH) 3 + Na 2 O = 2NaAlO 2 + 3H 2 O

All amphoteric hydroxides are weak electrolytes.

salt

salt- These are complex substances consisting of metal ions and an acid residue. Salts are products of complete or partial replacement of hydrogen ions by metal (or ammonium) ions in acids. Types of salts: medium (normal), acid and basic.

Medium salts- these are products of complete replacement of hydrogen cations in acids with metal (or ammonium) ions: Na 2 CO 3, NiSO 4, NH 4 Cl, etc.

Chemical properties of medium salts

1. Salts interact with acids, alkalis and other salts, forming either a weak electrolyte or a precipitate; or gas:

Ba(NO 3) 2 + H 2 SO 4 = BaSO 4 ¯ + 2HNO 3

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

CaCl 2 + 2AgNO 3 \u003d 2AgCl¯ + Ca (NO 3) 2

2CH 3 COONa + H 2 SO 4 = Na 2 SO 4 + 2CH 3 COOH

NiSO 4 + 2KOH \u003d Ni (OH) 2 ¯ + K 2 SO 4

base

NH 4 NO 3 + NaOH \u003d NH 3 + H 2 O + NaNO 3

2. Salts interact with more active metals. A more active metal displaces a less active metal from a salt solution (Appendix 3).

Zn + CuSO 4 \u003d ZnSO 4 + Cu

Acid salts- these are products of incomplete replacement of hydrogen cations in acids with metal (or ammonium) ions: NaHCO 3, NaH 2 PO 4, Na 2 HPO 4, etc. Acid salts can only be formed by polybasic acids. Almost all acidic salts are highly soluble in water.

Obtaining acid salts and converting them into medium

1. Acid salts are obtained by reacting an excess of acid or acid oxide with a base:

H 2 CO 3 + NaOH = NaHCO 3 + H 2 O

CO 2 + NaOH = NaHCO 3

2. When an excess of acid interacts with a basic oxide:

2H 2 CO 3 + CaO \u003d Ca (HCO 3) 2 + H 2 O

3. Acid salts are obtained from medium salts by adding acid:

eponymous

Na 2 SO 3 + H 2 SO 3 \u003d 2NaHSO 3;

Na 2 SO 3 + HCl \u003d NaHSO 3 + NaCl

4. Acid salts are converted to medium using alkali:

NaHCO 3 + NaOH = Na 2 CO 3 + H 2 O

Basic salts are products of incomplete substitution of hydroxo groups (OH - ) bases with an acidic residue: MgOHCl, AlOHSO 4, etc. Basic salts can only be formed by weak bases of polyvalent metals. These salts are generally sparingly soluble.

Obtaining basic salts and converting them to medium

1. Basic salts are obtained by reacting an excess of a base with an acid or acid oxide:

Mg(OH) 2 + HCl = MgOHCl¯ + H 2 O

hydroxo-

magnesium chloride

Fe(OH) 3 + SO 3 = FeOHSO 4 ¯ + H 2 O

hydroxo-

iron(III) sulfate

2. Basic salts are formed from an average salt by adding a lack of alkali:

Fe 2 (SO 4) 3 + 2NaOH \u003d 2FeOHSO 4 + Na 2 SO 4

3. Basic salts are converted to medium ones by adding an acid (preferably the one that corresponds to the salt):

MgOHCl + HCl \u003d MgCl 2 + H 2 O

2MgOHCl + H 2 SO 4 \u003d MgCl 2 + MgSO 4 + 2H 2 O

ELECTROLYTES

electrolytes- these are substances that decompose into ions in solution under the influence of polar solvent molecules (H 2 O). According to the ability to dissociate (decay into ions), electrolytes are conditionally divided into strong and weak. Strong electrolytes dissociate almost completely (in dilute solutions), while weak ones decompose into ions only partially.

Strong electrolytes include:

strong acids (see p. 20);

strong bases - alkalis (see p. 22);

almost all soluble salts.

Weak electrolytes include:

Weak acids (see p. 20);

bases are not alkalis;

One of the main characteristics of a weak electrolyte is dissociation constant – To . For example, for a monobasic acid,

HA Û H + + A - ,

where, is the equilibrium concentration of H + ions;

is the equilibrium concentration of acid anions A - ;

is the equilibrium concentration of acid molecules,

Or for a weak foundation,

MOH Û M + +OH - ,

,

where, is the equilibrium concentration of cations M + ;

– equilibrium concentration of hydroxide ions OH - ;

is the equilibrium concentration of weak base molecules.

Dissociation constants of some weak electrolytes (at t = 25°С)

Substance	To	Substance	To
HCOOH	K = 1.8×10 -4	H3PO4	K 1 \u003d 7.5 × 10 -3
CH3COOH	K = 1.8×10 -5		K 2 \u003d 6.3 × 10 -8
HCN	K = 7.9×10 -10		K 3 \u003d 1.3 × 10 -12
H2CO3	K 1 \u003d 4.4 × 10 -7	HClO	K = 2.9×10 -8
	K 2 \u003d 4.8 × 10 -11	H3BO3	K 1 \u003d 5.8 × 10 -10
HF	K = 6.6×10 -4		K 2 \u003d 1.8 × 10 -13
HNO 2	K = 4.0×10 -4		K 3 \u003d 1.6 × 10 -14
H2SO3	K 1 \u003d 1.7 × 10 -2	H2O	K = 1.8×10 -16
	K 2 \u003d 6.3 × 10 -8	NH 3 × H 2 O	K = 1.8×10 -5
H 2 S	K 1 \u003d 1.1 × 10 -7	Al(OH)3	K 3 \u003d 1.4 × 10 -9
	K 2 \u003d 1.0 × 10 -14	Zn(OH) 2	K 1 \u003d 4.4 × 10 -5
H2SiO3	K 1 \u003d 1.3 × 10 -10		K 2 \u003d 1.5 × 10 -9
	K 2 \u003d 1.6 × 10 -12	Cd(OH)2	K 2 \u003d 5.0 × 10 -3
Fe(OH)2	K 2 \u003d 1.3 × 10 -4	Cr(OH)3	K 3 \u003d 1.0 × 10 -10
Fe(OH)3	K 2 \u003d 1.8 × 10 -11	Ag(OH)	K = 1.1×10 -4
	K 3 \u003d 1.3 × 10 -12	Pb(OH)2	K 1 \u003d 9.6 × 10 -4
Cu(OH)2	K 2 \u003d 3.4 × 10 -7		K 2 \u003d 3.0 × 10 -8
Ni(OH)2	K 2 \u003d 2.5 × 10 -5