Acid hydroxides are inorganic compounds of the hydroxyl group -OH and a metal or non-metal with an oxidation state of +5, +6. Another name is oxygen-containing inorganic acids. Their feature is the elimination of a proton during dissociation.

Classification of hydroxides

Hydroxides are also called hydroxides and hydrates. Almost everyone has them chemical elements, some have wide use in nature, for example, the minerals hydrargillite and brucite are aluminum and magnesium hydroxides, respectively.

The following types of hydroxides are distinguished:

• basic;
• amphoteric;
• acid.

The classification is based on whether the oxide forming the hydroxide is basic, acidic, or amphoteric.

General properties

Of greatest interest are the acid-base properties of oxides and hydroxides, since the possibility of reactions depends on them. Whether the hydroxide will exhibit acidic, basic, or amphoteric properties depends on the strength of the bond between the oxygen, hydrogen, and element.

The strength is affected by the ionic potential, with an increase in which the basic properties of hydroxides weaken and the acidic properties of hydroxides increase.

Higher hydroxides

Higher hydroxides are compounds in which the forming element is in the highest oxidation state. These are among all types in the class. An example of a base is magnesium hydroxide. Aluminum hydroxide is amphoteric, while perchloric acid can be classified as an acidic hydroxide.

The change in the characteristics of these substances depending on the forming element can be traced according to the periodic system of D. I. Mendeleev. The acidic properties of higher hydroxides increase from left to right, while the metallic properties, respectively, weaken in this direction.

Basic hydroxides

In a narrow sense, this type is called a base, since the OH anion is split off during its dissociation. The most famous of these compounds are alkalis, for example:

• Slaked lime Ca(OH) 2 used in whitewashing rooms, tanning leather, preparing antifungal liquids, mortars and concrete, softening water, producing sugar, bleach and fertilizers, caustifying sodium and potassium carbonates, neutralizing acidic solutions, detecting carbon dioxide , disinfection, reduction resistivity soil, as a food additive.
• Caustic potash KOH used in photography, oil refining, food, paper and metallurgical production, as well as an alkaline battery, acid neutralizer, catalyst, gas cleaner, pH regulator, electrolyte, component of detergents, drilling fluids, dyes, fertilizers, potassium organic and inorganic substances, pesticides, pharmaceutical preparations for the treatment of warts, soaps, synthetic rubber.
• NaOH, necessary for the pulp and paper industry, saponification of fats in the production of detergents, neutralization of acids, the manufacture of biodiesel fuel, the dissolution of blockages, the degassing of toxic substances, the processing of cotton and wool, the washing of molds, food production, cosmetology, photography.

Basic hydroxides are formed as a result of interaction with water of the corresponding metal oxides, in the vast majority of cases with an oxidation state of +1 or +2. These include alkali, alkaline earth and transition elements.

In addition, bases can be obtained in the following ways:

• the interaction of alkali with a salt of a low-active metal;
• a reaction between an alkaline or alkaline earth element and water;
• electrolysis of an aqueous solution of salt.

Acid and basic hydroxides interact with each other to form salt and water. This reaction is called neutralization and has great importance for titrimetric analysis. In addition, it is used in everyday life. When acid is spilled, a dangerous reagent can be neutralized with soda, and vinegar is used for alkali.

In addition, basic hydroxides shift the ionic equilibrium during dissociation in solution, which manifests itself in a change in the colors of the indicators, and enter into exchange reactions.

When heated, insoluble compounds decompose into oxide and water, and alkalis melt. and an acidic oxide form a salt.

Amphoteric hydroxides

Some elements, depending on the conditions, exhibit either basic or acidic properties. Hydroxides based on them are called amphoteric. They are easy to identify by the metal included in the composition, which has an oxidation state of +3, +4. For example, a white gelatinous substance - aluminum hydroxide Al (OH) 3, used in water purification due to its high adsorbing capacity, in the manufacture of vaccines as a substance that enhances the immune response, in medicine for the treatment of acid-dependent diseases of the gastrointestinal tract. It is also often included in flame retardant plastics and acts as a carrier for catalysts.

But there are exceptions when the value of the oxidation state of the element is +2. This is typical for beryllium, tin, lead and zinc. Hydroxide of the last metal Zn(OH) 2 is widely used in chemical industries, primarily for the synthesis of various compounds.

Amphoteric hydroxide can be obtained by reacting a solution of a transition metal salt with dilute alkali.

Amphoteric hydroxide and acid oxide, alkali or acid form a salt when interacting. Heating the hydroxide leads to its decomposition into water and metahydroxide, which, upon further heating, is converted into an oxide.

Amphoteric and acidic hydroxides behave similarly in an alkaline medium. When interacting with acids, amphoteric hydroxides act as bases.

Acid hydroxides

This type is characterized by the presence in the composition of the element in the oxidation state from +4 to +7. In solution, they are able to donate a hydrogen cation or accept an electron pair and form covalent bond. Most often they have state of aggregation liquids, but there are also solids among them.

Forms a hydroxide acidic oxide capable of salt formation and containing a non-metal or transition metal. The oxide is obtained as a result of the oxidation of a non-metal, the decomposition of an acid or salt.

Acidic ones are manifested in their ability to color indicators, dissolve active metals with the release of hydrogen, and react with bases and basic oxides. Their distinctive feature is participation in redox reactions. During chemical process they attach negatively charged elementary particles. The ability to act as an electron acceptor weakens upon dilution and conversion to salts.

Thus, it is possible to distinguish not only the acid-base properties of hydroxides, but also the oxidizing ones.

Nitric acid

HNO 3 is considered a strong monobasic acid. It is very poisonous, leaves ulcers on the skin with yellow staining of the integument, and its vapors instantly irritate the respiratory mucosa. The outdated name is strong vodka. It belongs to acidic hydroxides; in aqueous solutions it completely dissociates into ions. Outwardly, it looks like a colorless liquid fuming in air. An aqueous solution is considered concentrated, which includes 60 - 70% of the substance, and if the content exceeds 95%, it is called fuming nitric acid.

The higher the concentration, the darker the liquid appears. It may even have a brown color due to decomposition into oxide, oxygen and water in the light or with slight heating, so it should be stored in a dark glass container in a cool place.

The chemical properties of acid hydroxide are such that it can only be distilled without decomposition under reduced pressure. All metals react with it except gold, some representatives of the platinum group and tantalum, but the final product depends on the concentration of the acid.

For example, a 60% substance, when interacting with zinc, gives nitrogen dioxide as the predominant by-product, 30% - monoxide, 20% - dinitrogen oxide (laughing gas). Even lower concentrations of 10% and 3% give a simple substance nitrogen in the form of gas and ammonium nitrate, respectively. Thus, various nitro compounds can be obtained from the acid. As can be seen from the example, the lower the concentration, the deeper the reduction of nitrogen. It also affects the activity of the metal.

A substance can dissolve gold or platinum only in the composition of aqua regia - a mixture of three parts of hydrochloric and one nitric acid. Glass and polytetrafluoroethylene are resistant to it.

In addition to metals, the substance reacts with basic and amphoteric oxides, bases, and weak acids. In all cases, the result is salts, with non-metals - acids. Not all reactions occur safely, for example, amines and turpentine spontaneously ignite when in contact with hydroxide in a concentrated state.

Salts are called nitrates. When heated, they decompose or exhibit oxidizing properties. In practice, they are used as fertilizers. They practically do not occur in nature due to their high solubility, therefore, all salts except potassium and sodium are obtained artificially.

The acid itself is obtained from synthesized ammonia and, if necessary, concentrated in several ways:

• shifting the balance by increasing the pressure;
• heating in the presence of sulfuric acid;
• distillation.

Further, it is used in the production of mineral fertilizers, dyes and medicines, the military industry, easel graphics, jewelry, and organic synthesis. Occasionally, dilute acid is used in photography to acidify tinting solutions.

Sulphuric acid

H 2 SO 4 is a strong dibasic acid. It looks like a colorless heavy oily liquid, odorless. The obsolete name is vitriol (aqueous solution) or vitriol oil (mixture with sulfur dioxide). This name was given due to the fact that early XIX For centuries, sulfur has been produced in vitriol plants. In tribute to tradition, sulfate hydrates are still called vitriol to this day.

Acid production is established in industrial scale and is about 200 million tons per year. It is obtained by oxidizing sulfur dioxide with oxygen or nitrogen dioxide in the presence of water, or by reacting hydrogen sulfide with copper, silver, lead or mercury sulfate. The resulting concentrated substance is a strong oxidizing agent: it displaces halogens from the corresponding acids, converts carbon and sulfur into acid oxides. The hydroxide is then reduced to sulfur dioxide, hydrogen sulfide or sulfur. A dilute acid usually does not exhibit oxidizing properties and forms medium and acidic salts or esters.

The substance can be detected and identified by reaction with soluble barium salts, as a result of which a white precipitate of sulfate precipitates.

Further, the acid is used in the processing of ores, the production of mineral fertilizers, chemical fibers, dyes, smoke-forming and explosives, various industries, organic synthesis, as an electrolyte, for obtaining mineral salts.

But the use is associated with certain dangers. Corrosive substance causes chemical burns on contact with skin or mucous membranes. When inhaled, a cough first appears, and subsequently - inflammatory diseases of the larynx, trachea, and bronchi. Exceeding the maximum allowable concentration of 1 mg per cubic meter is deadly.

You can encounter sulfuric acid vapors not only in specialized industries, but also in the atmosphere of the city. This happens when chemical and metallurgical plants emit sulfur oxides, which then fall out as acid rain.

All these dangers have led to the fact that the circulation of more than 45% mass concentration in Russia is limited.

sulfurous acid

H 2 SO 3 is a weaker acid than sulfuric acid. Its formula differs by only one oxygen atom, but this makes it unstable. It has not been isolated in the free state; it exists only in dilute aqueous solutions. They can be identified by a specific pungent smell, reminiscent of a burnt match. And to confirm the presence of a sulfite ion - by reaction with potassium permanganate, as a result of which the red-violet solution becomes colorless.

A substance under different conditions can act as a reducing agent and an oxidizing agent, form acidic and medium salts. It is used for food preservation, obtaining cellulose from wood, as well as for delicate bleaching of wool, silk and other materials.

Orthophosphoric acid

H 3 RO 4 is an acid of medium strength, which looks like colorless crystals. Orthophosphoric acid is also called an 85% solution of these crystals in water. It appears as an odorless, syrupy liquid that is prone to hypothermia. Heating above 210 degrees Celsius leads to its transformation into pyrophosphoric acid.

Orthophosphoric acid is highly soluble in water, neutralized by alkalis and ammonia hydrate, reacts with metals, and forms polymeric compounds.

You can get the substance in different ways:

• dissolving red phosphorus in water under pressure, at a temperature of 700-900 degrees, using platinum, copper, titanium or zirconium;
• boiling red phosphorus in concentrated nitric acid;
• adding hot concentrated nitric acid to the phosphine;
• oxidation of oxygen phosphine at 150 degrees;
• exposure to tetraphosphorus decaoside with a temperature of 0 degrees, then its gradual increase to 20 degrees and a smooth transition to boiling (water is needed at all stages);
• by dissolving pentachloride or phosphorus oxide trichloride in water.

The application of the resulting product is wide. It helps to reduce surface tension and remove oxides from surfaces preparing for soldering, clean metals from rust and create a protective film on their surface that prevents further corrosion. In addition, orthophosphoric acid is used in industrial freezers and for research in molecular biology.

Also, the compound is part of aviation hydraulic fluids, food additives and acidity regulators. It is used in fur farming for the prevention of urolithiasis in minks and in dentistry for manipulations prior to filling.

pyrophosphoric acid

H 4 P 2 O 7 is an acid characterized as strong in the first step and weak in the rest. It melts without decomposition, since this process requires heating in a vacuum or the presence of strong acids. It is neutralized by alkalis and reacts with hydrogen peroxide. Get it in one of the following ways:

• decomposition of tetraphosphorus decaoxide in water at zero temperature, and then heating it to 20 degrees;
• heating orthophosphoric acid to 150 degrees;
• interaction of concentrated phosphoric acid with tetraphosphorus decaoxide at 80-100 degrees.

The product is mainly used for the production of fertilizers.

In addition to these, there are many other representatives of acid hydroxides. Each of them has its own characteristics and characteristics, but in general, the acidic properties of oxides and hydroxides lie in their ability to split off hydrogen, decompose, interact with alkalis, salts and metals.

Hydroxides- this is an electrolyte during the dissociation of which in aqueous solutions a metal cation and a negatively charged hydroxide anion are formed.

Hydroxides, except for: bases of alkali and alkaline earth metals, as well as amphoteric hydroxides, are practically insoluble in water.

Basic hydroxides (bases) - only metal hydroxides with an oxidation state of +1, +2

A M F O T E R N Y E. HY D R O X I D Y.

Amphoteric hydroxides- these are hydroxides which, when dissociated in aqueous solutions, can form both H + and OH -

Amphoteric hydroxides, hydroxides of metals with an oxidation state of +3, +4 and several metals with an oxidation state of +2

Properties:

1. Amphoteric hydroxides react with alkalis.

2. Amphoteric hydroxides react with acids.

ACID E. HYDRO OXIDE.

Acid hydroxides- hydroxides that exhibit the properties of acids - HNO 3, H 3 PO 4

Properties:

The properties of acidic hydroxides are, respectively, the opposite of those of alkaline hydroxides.

Question 18

Question 19 (see question 11!!)

Question 20

The concept of a state function. Examples.

System state function − some analytical function that depends on the thermodynamic parameters of the system in a given state. The value does not depend on the history of the system, and when passing from one state to another, it does not depend on the path of the process. It is determined only by the initial and final state of the system.

∆U 1.2 \u003d U 2 -U 1

Question 21

Salt. Classification. Structural formulas. Receipt.

Salts:

Sour 2) Medium 3) Basic

Medium salt- this is an electrolyte during the dissociation of which in an aqueous solution a metal cation and an anion of an acid residue are formed

Conditions for obtaining medium salt

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

Medium salt is formed when the reaction proceeds in strictly stoichiometric ratios

Acid salt- this is an element during the dissociation of which a metal cation, a hydrogen cation and an anion of an acid residue are formed

Conditions for obtaining acid salts

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

Acid salts obtained with an excess of oxygen.

Basic salts- this is an electrolyte during the dissociation of which a metal cation is formed hydroxide anion and an anion of an acid residue

Receipt:

Acid + base

Acid + basic oxide
acid + salt
salt + salt

Base + acid oxide
lye + salt
basic oxide + acid oxide
metal + non-metal
metal + acid
metal + salt

Question 22

Enthalpy and entropy of formation of chemical substances.

Entropy- a function of the state of the system that shows the direction of the processes in nature. A measure of the chaos and disorder of a system.

Enthalpy is a measure of the energy accumulated by a substance during its formation

When entropy is maximum, enthalpy is minimum and vice versa.

Question 23

Types of chem. connections.

Electronegativity - the ability of atoms to pull electron density onto themselves.

Covalent bond - diatomic bond, 2 atoms and 2 electrons required. (strong connection, localized)

Ionic bond - the limiting case of a covalent polar bond; electrostatic interaction that occurs between cations and anions.

Universal connection - van der Waals intermolecular

Specific

1) Metal. All electrons form an electron gas

2) Hydrogen bond. Based on the property of H atoms bonded by a highly electronegative element.

Question 24.

Foundations – complex substances, consisting of a metal atom and one or more hydroxyl groups. General formula of bases Me(OH) n . Bases (from the point of view of the theory of electrolytic dissociation) are electrolytes that dissociate when dissolved in water with the formation of metal cations and hydroxide ions OH -.

Classification. Based on their solubility in water, bases are divided into alkalis(water-soluble bases) and bases insoluble in water . Alkalis form alkali and alkaline earth metals, as well as some other metal elements. According to acidity (the number of OH - ions formed during complete dissociation, or the number of dissociation steps), the bases are divided into single acid (with complete dissociation, one OH ion is obtained; one stage of dissociation) and polyacid (with complete dissociation, more than one OH ion is obtained; more than one dissociation step). Among the polyacid bases, there are two-acid(for example, Sn(OH) 2 ), triacid(Fe (OH) 3) and four-acid (Th(OH)4). One acid is, for example, the base KOH.

Allocate a group of hydroxides that exhibit chemical duality. They interact with both bases and acids. it amphoteric hydroxides ( cm. table 1).

Table 1 - Amphoteric hydroxides

physical properties. Bases are solids of various colors and varying solubility in water.

Chemical properties of bases

1) Dissociation: KOH + n H 2 O K + × m H 2 O + OH - × d H 2 O or abbreviated: KOH K + + OH -.

Polyacid bases dissociate in several steps (mostly dissociation occurs in the first step). For example, the two-acid base Fe (OH) 2 dissociates in two steps:

Fe(OH) 2 FeOH + + OH – (1 stage);

FeOH + Fe 2+ + OH - (stage 2).

2) Interaction with indicators(alkalis turn purple litmus blue, methyl orange yellow, and phenolphthalein raspberry):

indicator + OH - ( alkali) colored compound.

3 ) Decomposition with the formation of oxide and water (see. table 2). Hydroxides alkali metals are resistant to heat (melt without decomposition). Hydroxides of alkaline earth and heavy metals usually decompose easily. The exception is Ba(OH) 2, in which t diff is high enough (approximately 1000° C).

Zn(OH) 2 ZnO + H 2 O.

Table 2 - Decomposition temperatures for some metal hydroxides

4 ) The interaction of alkalis with some metals(e.g. Al and Zn):

In solution: 2Al + 2NaOH + 6H 2 O ® 2Na + 3H 2

2Al + 2OH - + 6H 2 O ® 2 - + 3H 2.

When fused: 2Al + 2NaOH + 2H 2 O 2NaAl O 2 + 3H 2.

5 ) Interaction of alkalis with non-metals:

6 NaOH + 3Cl 2 5Na Cl + NaClO 3 + 3H 2 O.

6) Interaction of alkalis with acidic and amphoteric oxides:

2NaOH + CO 2 ® Na 2 CO 3 + H 2 O 2OH - + CO 2 ® CO 3 2- + H 2 O.

In solution: 2NaOH + ZnO + H 2 O ® Na 2 2OH - + ZnO + H 2 O ® 2–.

When fused with amphoteric oxide: 2NaOH + ZnO Na 2 ZnO 2 + H 2 O.

7) Reaction of bases with acids:

H 2 SO 4 + Ca(OH) 2 ® CaSO 4 ¯ + 2H 2 O 2H + + SO 4 2– + Ca 2+ +2OH - ® CaSO 4 ¯ + 2H 2 O

H 2 SO 4 + Zn (OH) 2 ® ZnSO 4 + 2H 2 O 2H + + Zn (OH) 2 ® Zn 2+ + 2H 2 O.

8) Interaction of alkalis with amphoteric hydroxides(cm. table 1):

In solution: 2NaOH + Zn(OH) 2 ® Na 2 2OH – + Zn(OH) 2 ® 2–

When fused: 2NaOH + Zn(OH) 2 Na 2 ZnO 2 + 2H 2 O.

9 ) The interaction of alkalis with salts. Salts react with a base that is insoluble in water. :

CuS О 4 + 2NaOH ® Na 2 SO 4 + Cu(OH) 2 ¯ Cu 2+ + 2OH - ® Cu(OH) 2 ¯.

Receipt. Bases insoluble in water obtained by reacting the corresponding salt with alkali:

2NaOH + ZnS О 4 ® Na 2 SO 4 + Zn(OH) 2 ¯ Zn 2+ + 2OH - ® Zn(OH) 2 ¯.

Alkalis receive:

1) The interaction of metal oxide with water:

Na 2 O + H 2 O ® 2NaOH CaO + H 2 O ® Ca (OH) 2.

2) Interaction of alkali and alkaline earth metals with water:

2Na + H 2 O ® 2NaOH + H 2 Ca + 2H 2 O ® Ca (OH) 2 + H 2.

3) Electrolysis of salt solutions:

2NaCl + 2H 2 O H 2 + 2NaOH + Cl 2.

4 ) Exchange interaction of hydroxides of alkaline earth metals with some salts. In the course of the reaction, an insoluble salt must necessarily be obtained. .

Ba(OH) 2 + Na 2 CO 3 ® 2NaOH + BaCO 3 ¯ Ba 2 + + CO 3 2 - ® BaCO 3 ¯.

L.A. Yakovishin

Bases (hydroxides)- complex substances, the molecules of which have one or more OH hydroxyl groups in their composition. Most often, bases consist of a metal atom and an OH group. For example, NaOH is sodium hydroxide, Ca (OH) 2 is calcium hydroxide, etc.

There is a base - ammonium hydroxide, in which the hydroxy group is attached not to the metal, but to the NH 4 + ion (ammonium cation). Ammonium hydroxide is formed by dissolving ammonia in water (reactions of addition of water to ammonia):

NH 3 + H 2 O = NH 4 OH (ammonium hydroxide).

The valence of the hydroxyl group is 1. The number of hydroxyl groups in the base molecule depends on the valency of the metal and is equal to it. For example, NaOH, LiOH, Al (OH) 3, Ca (OH) 2, Fe (OH) 3, etc.

All grounds - solids which have different colors. Some bases are highly soluble in water (NaOH, KOH, etc.). However, most of them do not dissolve in water.

Water-soluble bases are called alkalis. Alkali solutions are "soapy", slippery to the touch and quite caustic. Alkalis include hydroxides of alkali and alkaline earth metals (KOH, LiOH, RbOH, NaOH, CsOH, Ca(OH) 2, Sr(OH) 2, Ba(OH) 2, etc.). The rest are insoluble.

Insoluble bases- these are amphoteric hydroxides, which, when interacting with acids, act as bases, and behave like acids with alkali.

Different bases differ in their ability to split off hydroxy groups, so they are divided into strong and weak bases according to the feature.

Strong bases easily donate their hydroxyl groups in aqueous solutions, but weak bases do not.

Chemical properties of bases

The chemical properties of bases are characterized by their relationship to acids, acid anhydrides and salts.

1. Act on indicators. Indicators change their color depending on the interaction with different chemicals. In neutral solutions - they have one color, in acid solutions - another. When interacting with bases, they change their color: the methyl orange indicator turns into yellow, the litmus indicator turns blue, and phenolphthalein becomes fuchsia.

2. interact with acid oxides With formation of salt and water:

2NaOH + SiO 2 → Na 2 SiO 3 + H 2 O.

3. React with acids, forming salt and water. The reaction of the interaction of a base with an acid is called a neutralization reaction, since after its completion the medium becomes neutral:

2KOH + H 2 SO 4 → K 2 SO 4 + 2H 2 O.

4. React with salts forming a new salt and base:

2NaOH + CuSO 4 → Cu(OH) 2 + Na 2 SO 4.

5. Able to decompose into water and basic oxide when heated:

Cu (OH) 2 \u003d CuO + H 2 O.

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Before discussing the chemical properties of bases and amphoteric hydroxides, let's clearly define what it is?

1) Bases or basic hydroxides include metal hydroxides in the oxidation state +1 or +2, i.e. the formulas of which are written either as MeOH or as Me(OH) 2 . However, there are exceptions. So, the hydroxides Zn (OH) 2, Be (OH) 2, Pb (OH) 2, Sn (OH) 2 do not belong to the bases.

2) Amphoteric hydroxides include metal hydroxides in the oxidation state +3, +4, and, as exceptions, hydroxides Zn (OH) 2, Be (OH) 2, Pb (OH) 2, Sn (OH) 2. Metal hydroxides in the oxidation state +4, in USE assignments do not meet, therefore will not be considered.

Chemical properties of bases

All bases are divided into:

Recall that beryllium and magnesium are not alkaline earth metals.

In addition to being soluble in water, alkalis also dissociate very well in aqueous solutions, while insoluble bases have a low degree of dissociation.

This difference in solubility and ability to dissociate between alkalis and insoluble hydroxides leads, in turn, to noticeable differences in their chemical properties. So, in particular, alkalis are more chemically active compounds and are often capable of entering into those reactions that insoluble bases do not enter into.

Reaction of bases with acids

Alkalis react with absolutely all acids, even very weak and insoluble ones. For example:

Insoluble bases react with almost all soluble acids, do not react with insoluble silicic acid:

It should be noted that both strong and weak bases with general formula species Me (OH) 2 can form basic salts with a lack of acid, for example:

Interaction with acid oxides

Alkalis react with all acidic oxides to form salts and often water:

Insoluble bases are able to react with all higher acid oxides corresponding to stable acids, for example, P 2 O 5, SO 3, N 2 O 5, with the formation of medium salts:

Insoluble bases of the form Me (OH) 2 react in the presence of water with carbon dioxide exclusively with the formation of basic salts. For example:

Cu(OH) 2 + CO 2 = (CuOH) 2 CO 3 + H 2 O

With silicon dioxide, due to its exceptional inertness, only the strongest bases, alkalis, react. In this case, normal salts are formed. The reaction does not proceed with insoluble bases. For example:

Interaction of bases with amphoteric oxides and hydroxides

All alkalis react with amphoteric oxides and hydroxides. If the reaction is carried out by fusing an amphoteric oxide or hydroxide with a solid alkali, such a reaction leads to the formation of hydrogen-free salts:

If aqueous solutions of alkalis are used, then hydroxo complex salts are formed:

In the case of aluminum, under the action of an excess of concentrated alkali, instead of the Na salt, the Na 3 salt is formed:

The interaction of bases with salts

Any base reacts with any salt only if two conditions are met simultaneously:

1) solubility of starting compounds;

2) the presence of a precipitate or gas among the reaction products

For example:

Thermal stability of bases

All alkalis, except Ca(OH) 2 , are resistant to heat and melt without decomposition.

All insoluble bases, as well as slightly soluble Ca (OH) 2, decompose when heated. Most heat decomposition of calcium hydroxide - about 1000 o C:

Insoluble hydroxides have much lower decomposition temperatures. So, for example, copper (II) hydroxide decomposes already at temperatures above 70 o C:

Chemical properties of amphoteric hydroxides

Interaction of amphoteric hydroxides with acids

Amphoteric hydroxides react with strong acids:

Amphoteric metal hydroxides in the +3 oxidation state, i.e. type Me (OH) 3, do not react with acids such as H 2 S, H 2 SO 3 and H 2 CO 3 due to the fact that salts that could be formed as a result of such reactions are subject to irreversible hydrolysis to the original amphoteric hydroxide and corresponding acid:

Interaction of amphoteric hydroxides with acid oxides

Amphoteric hydroxides react with higher oxides, which correspond to stable acids (SO 3, P 2 O 5, N 2 O 5):

Amphoteric metal hydroxides in the +3 oxidation state, i.e. type Me (OH) 3, do not react with acid oxides SO 2 and CO 2.

Interaction of amphoteric hydroxides with bases

Of the bases, amphoteric hydroxides react only with alkalis. In this case, if an aqueous solution of alkali is used, then hydroxo complex salts are formed:

And when amphoteric hydroxides are fused with solid alkalis, their anhydrous analogues are obtained:

Interaction of amphoteric hydroxides with basic oxides

Amphoteric hydroxides react when fused with oxides of alkali and alkaline earth metals:

Thermal decomposition of amphoteric hydroxides

All amphoteric hydroxides are insoluble in water and, like any insoluble hydroxides, decompose when heated to the corresponding oxide and water.