Methods for obtaining hydroxides. Chemical properties of hydroxides. Interaction of amphoteric hydroxides with basic oxides

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 are widely distributed 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, reduce soil resistivity, 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, pharmaceuticals 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 is of 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 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 a state of aggregation of a liquid, 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 involved in redox reactions. During the chemical process, they attach negatively charged elementary particles to themselves. 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.

Chemical properties acid hydroxide are such that it can be distilled without decomposition only 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.

It is then used in production. mineral fertilizers, dyes and drugs, military industry, easel graphics, jewelry, organic synthesis. Occasionally, dilute acid is used in photography to acidify tinting solutions.

Sulfuric 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 on an 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.

In the future, 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, to obtain 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 then - inflammatory diseases larynx, trachea, bronchi. Exceeding the maximum permissible concentration of 1 mg per cubic meter 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 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. With its help, surface tension is reduced and oxides are removed from surfaces preparing for soldering, metals are cleaned of rust and a protective film is created on their surface that prevents further corrosion. In addition, phosphoric 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.

Potassium, sodium or lithium may interact with water. In this case, compounds related to hydroxides are found in the reaction products. The properties of these substances, the features of the course of chemical processes in which bases are involved, are due to the presence of a hydroxyl group in their molecules. So, in the reactions of electrolytic dissociation, bases are split into metal ions and OH - anions. How bases interact with non-metal oxides, acids and salts, we will consider in our article.

Nomenclature and structure of the molecule

To correctly name the base, you need to add the word hydroxide to the name of the metal element. Let's bring concrete examples. The aluminum base belongs to amphoteric hydroxides, the properties of which we will consider in the article. Mandatory presence in base molecules of a hydroxyl group associated with a metal cation ion type bonds can be determined using indicators such as phenolphthalein. In an aqueous medium, an excess of OH - ions is determined by a change in the color of the indicator solution: colorless phenolphthalein becomes crimson. If a metal exhibits multiple valences, it can form multiple bases. For example, iron has two bases, in which it is equal to 2 or 3. The first compound is characterized by signs of the second - amphoteric. Therefore, the properties of higher hydroxides differ from compounds in which the metal has a lower degree of valency.

Physical characteristic

Bases are solids that are resistant to heat. In relation to water, they are divided into soluble (alkali) and insoluble. The first group is formed by chemically active metals - elements of the first and second groups. Water-insoluble substances are composed of atoms of other metals, whose activity is inferior to sodium, potassium or calcium. Examples of such compounds are iron or copper bases. The properties of hydroxides will depend on which group of substances they belong to. So, alkalis are thermally stable and do not decompose when heated, while water-insoluble bases under the action of high temperature break down to form oxide and water. For example, a copper base decomposes as follows:

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

Chemical properties of hydroxides

The interaction between the two most important groups of compounds - acids and bases - is called in chemistry a neutralization reaction. This name can be explained by the fact that chemically aggressive hydroxides and acids form neutral products - salts and water. Being, in fact, an exchange process between two complex substances, neutralization is characteristic of both alkalis and water-insoluble bases. Here is the equation for the neutralization reaction between caustic potash and hydrochloric acid:

KOH + HCl \u003d KCl + H 2 O

An important property of alkali metal bases is their ability to react with acidic oxides, resulting in salt and water. For example, by passing carbon dioxide through sodium hydroxide, you can get its carbonate and water:

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

Ion exchange reactions include the interaction between alkalis and salts, which leads to the formation of insoluble hydroxides or salts. So, pouring the solution dropwise into a solution of copper sulfate, you can get a blue jelly-like precipitate. It is a copper base, insoluble in water:

CuSO 4 + 2NaOH \u003d Cu (OH) 2 + Na 2 SO 4

The chemical properties of hydroxides, insoluble in water, differ from alkalis in that they lose water upon slight heating - they dehydrate, turning into the form of the corresponding basic oxide.

Bases exhibiting dual properties

If an element or can react with both acids and alkalis, it is called amphoteric. These include, for example, zinc, aluminum and their bases. The properties of amphoteric hydroxides make it possible to write down their molecular formulas both in isolating the hydroxo group and in the form of acids. Let us present several equations for the reactions of an aluminum base with hydrochloric acid and sodium hydroxide. They illustrate special properties hydroxides related to amphoteric compounds. The second reaction takes place with the decay of alkali:

2Al(OH) 3 + 6HCl = 2AlCl 3 + 3H 2 O

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

The products of the processes will be water and salts: aluminum chloride and sodium aluminate. All amphoteric bases are insoluble in water. They are obtained as a result of the interaction of the corresponding salts and alkalis.

Methods of obtaining and application

In industry requiring large volumes of alkalis, they are obtained by electrolysis of salts containing cations of active metals of the first and second groups of the periodic system. The raw material for the extraction, for example, caustic sodium, is a solution of common salt. The reaction equation will be:

2NaCl + 2H 2 O \u003d 2NaOH + H 2 + Cl 2

The bases of low-active metals in the laboratory are obtained by the interaction of alkalis with their salts. The reaction belongs to the type of ion exchange and ends with the precipitation of the base. A simple way to obtain alkalis is a substitution reaction between the active metal and water. It is accompanied by heating of the reacting mixture and belongs to the exothermic type.

The properties of hydroxides are used in industry. Alkalis play a special role here. They are used as cleaners for kerosene and gasoline, for the production of soap, processing of natural leather, as well as in technologies for the production of rayon and paper.

Physical Properties

The general formula of alkali metal hydroxides is MON.

All alkali metal hydroxides are colorless hygroscopic substances, easily deliquescent in air, very well soluble in water and ethanol, with the transition from LiOH to CsOH, the solubility increases.

Some physical properties alkali metal hydroxides are shown in the table.

Chemical properties

Hydroxides of all alkali metals melt without decomposition, lithium hydroxide decomposes when heated to a temperature of 600 ° C:

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

All hydroxides exhibit the properties of strong bases. In water, they dissociate almost completely:

NaOH \u003d Na + + OH -.

React with oxides of non-metals:

KOH + CO 2 \u003d KHCO 3;

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

2KOH + 2NO 2 = KNO 3 + KNO 2 + H 2 O.

Interact with acids, enter into a neutralization reaction:

NaOH + HCl \u003d NaCl + H 2 O;

KOH + HNO 3 \u003d KNO 3 + H 2 O.

Enter into exchange reactions with salts:

2NaOH + CuCl 2 = Cu(OH) 2 + 2NaCl.

React with halogens:

2KOH + Cl 2 \u003d KClO + KCl + H 2 O (in the cold);

6KOH + 3Cl 2 \u003d KClO 3 + 5KCl + 3H 2 O (when heated).

In the molten state, they interact with amphoteric metals and their oxides:

2KOH + Zn \u003d K 2 ZnO 2 + H 2;

2KOH + ZnO = K 2 ZnO 2 + H 2 O.

Aqueous solutions of hydroxides, when interacting with amphoteric metals, their oxides and hydroxides, form hydroxo complexes:

2NaOH + Be + 2H 2 O \u003d Na 2 + H 2;

2NaOH + BeO + H 2 O \u003d Na 2;

2NaOH + Be(OH) 2 = Na 2 .

Aqueous solutions and melts of hydroxides react with boron and silicon, their oxides and acids:

4NaOH + 4B + 3O 2 = 4NaBO 2 + 2H 2 O (melt);

2NaOH + Si + H 2 O = Na 2 SiO 3 + 2H 2 (solution).

Receipt

Lithium, sodium and potassium hydroxides are obtained by electrolysis of concentrated solutions of their chlorides, while hydrogen is released at the cathode, chlorine is formed at the anode:

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

Rubidium and cesium hydroxides are obtained from their salts using exchange reactions:

Rb 2 SO 4 + Ba (OH) 2 \u003d 2RbOH + BaSO 4.

ALKALINE EARTH METALS

Properties of alkaline earth metals

atomic number	Name	Atomic mass	Electronic configuration	r g/cm 3	t°pl. °C	t°boiling °C	EO	Atomic radius, nm	Oxidation state
	Beryllium Be	9,01	2s 2	1,86			1,5	0,113	+2
	Magnesium Mg	24,3	3s 2	1,74	649,5		1,2	0,16	+2
	Calcium Ca	40,08	4s 2	1,54			1,0	0,2	+2
	Strontium Sr	87,62	5s 2	2,67			1,0	0,213	+2
	Barium Ba	137,34	6s 2	3,61			0,9	0,25	+2
	Radium Ra		7s 2	~6	~700		0,9	–	+2

Physical Properties

Alkaline earth metals (compared to alkali metals) have higher t°pl. and t ° boiling., ionization potentials, densities and hardness.

Chemical properties

1. Very reactive.

2. Have a positive valence of +2.

3. React with water at room temperature(except for Be) with evolution of hydrogen.

4. They have a high affinity for oxygen (reducing agents).

5. They form salt-like hydrides EH 2 with hydrogen.

6. Oxides have the general formula EO. The tendency towards the formation of peroxides is less pronounced than for alkali metals.

Being in nature

3BeO Al 2 O 3 6SiO 2 - beryl

MgCO 3 - magnesite

CaCO 3 MgCO 3 - dolomite

KCl MgSO 4 3H 2 O - kainite

KCl MgCl 2 6H 2 O - carnallite

CaCO 3 - calcite (limestone, marble, etc.)

Ca 3 (PO 4) 2 - apatite, phosphorite

CaSO 4 2H 2 O - gypsum

CaSO 4 - anhydrite

CaF 2 - fluorspar (fluorite)

SrSO 4 - celestine

SrCO 3 - strontianite

BaSO 4 - barite

BaCO 3 - witherite

Receipt

Beryllium is obtained by reduction of fluoride:

BeF 2 + Mg - t ° ® Be + MgF 2

Barium is obtained by oxide reduction:

3BaO + 2Al - t ° ® 3Ba + Al 2 O 3

The remaining metals are obtained by electrolysis of chloride melts:

CaCl 2 ® Ca + Cl 2

cathode: Ca 2+ + 2ē ® Ca 0

anode: 2Cl - – 2ē ® Cl 0 2

Metals of the main subgroup of group II are strong reducing agents; in compounds, they exhibit only the +2 oxidation state. The activity of metals and their reducing ability increases in the series: ––Be–Mg–Ca–Sr–Ba®

1. Reaction with water.

Under normal conditions, the surface of Be and Mg is covered with an inert oxide film, so they are resistant to water. In contrast, Ca, Sr and Ba dissolve in water to form hydroxides, which are strong bases:

Mg + 2H 2 O - t ° ® Mg (OH) 2 + H 2

Ca + 2H 2 O ® Ca (OH) 2 + H 2

2. Reaction with oxygen.

All metals form oxides RO, barium peroxide - BaO 2:

2Mg + O 2 ® 2MgO

Ba + O 2 ® BaO 2

3. Binary compounds are formed with other non-metals:

Be + Cl 2 ® BeCl 2 (halides)

Ba + S ® BaS(sulfides)

3Mg + N 2 ® Mg 3 N 2 (nitrides)

Ca + H 2 ® CaH 2 (hydrides)

Ca + 2C ® CaC 2 (carbides)

3Ba + 2P ® Ba 3 P 2 (phosphides)

Beryllium and magnesium react relatively slowly with non-metals.

4. All metals dissolve in acids:

Ca + 2HCl ® CaCl 2 + H 2

Mg + H 2 SO 4 (razb.) ® MgSO 4 + H 2

Beryllium also dissolves in aqueous solutions of alkalis:

Be + 2NaOH + 2H 2 O ® Na 2 + H 2

5. Qualitative reaction to alkaline earth metal cations - coloring of the flame in the following colors:

Ca 2+ - dark orange

Sr 2+ - dark red

Ba 2+ - light green

The Ba 2+ cation is usually opened by an exchange reaction with sulfuric acid or its salts:

Barium sulfate is a white precipitate, insoluble in mineral acids.

Alkaline earth metal oxides

Receipt

1) Oxidation of metals (except Ba, which forms a peroxide)

2) Thermal decomposition of nitrates or carbonates

CaCO 3 - t ° ® CaO + CO 2

2Mg(NO 3) 2 - t ° ® 2MgO + 4NO 2 + O 2

Chemical properties

Typical basic oxides. React with water (except BeO), acid oxides and acids

MgO + H 2 O ® Mg (OH) 2

3CaO + P 2 O 5 ® Ca 3 (PO 4) 2

BeO + 2HNO 3 ® Be(NO 3) 2 + H 2 O

BeO - amphoteric oxide, soluble in alkalis:

BeO + 2NaOH + H 2 O ® Na 2

Alkaline earth metal hydroxides R(OH) 2

Receipt

Reactions of alkaline earth metals or their oxides with water:

Ba + 2H 2 O ® Ba (OH) 2 + H 2

CaO (quicklime) + H 2 O ® Ca (OH) 2 (slaked lime)

Chemical properties

Hydroxides R (OH) 2 - white crystalline substances, soluble in water worse than alkali metal hydroxides (the solubility of hydroxides decreases with decreasing serial number; Be (OH) 2 - insoluble in water, soluble in alkalis). The basicity of R(OH) 2 increases with increasing atomic number:

Be (OH) 2 - amphoteric hydroxide

Mg(OH) 2 - weak base

the remaining hydroxides are strong bases (alkalis).

1) Reactions with acid oxides:

Ca(OH) 2 + SO 2 ® CaSO 3 ¯ + H 2 O

Ba(OH) 2 + CO 2 ® BaCO 3 ¯ + H 2 O

2) Reactions with acids:

Mg (OH) 2 + 2CH 3 COOH ® (CH 3 COO) 2 Mg + 2H 2 O

Ba(OH) 2 + 2HNO 3 ® Ba(NO 3) 2 + 2H 2 O

3) Exchange reactions with salts:

Ba(OH) 2 + K 2 SO 4 ® BaSO 4 ¯+ 2KOH

4) The reaction of beryllium hydroxide with alkalis:

Be(OH) 2 + 2NaOH ® Na 2

Hardness of water

Natural water containing Ca 2+ and Mg 2+ ions is called hard. Hard water when boiled forms a scale, it does not boil soft food products; detergents do not give foam.

Carbonate (temporary) hardness is due to the presence of calcium and magnesium bicarbonates in water, non-carbonate (permanent) hardness - chlorides and sulfates.

The total hardness of water is considered as the sum of carbonate and non-carbonate.

Water hardness is removed by precipitation of Ca 2+ and Mg 2+ ions from the solution.

Hydrates of oxides are collectively called hydroxides. . Bases (basic hydroxides) are called hydrates of basic oxides. The general formula is Me( Oh) n. The number of hydroxyl groups (OH) in a molecule determines its acidity.

Most bases are insoluble in water, only Hydroxides alkaline and alkaline earthmetals (they are called alkalis), as well as ammonium . In aqueous solutions, bases dissociate into a metal cation hydroxyl group, amphoteric hydroxides dissociateboth as an acid and as a base . Polyacid bases dissociate in steps:

Me x + +xOH - ⇌ Me(OH) x ≡H x MeO x ⇌ x H + +MeO x x - (dissociation of amphoteric hydroxide (general scheme))

*This is interesting

Now there are 3 main theories of acids and bases:

1. Brønsted-Lowry protolithic theory .In it acid-a molecule or ion capable of being a donor in a given reaction protons , respectively, the bases are molecules or ions that attach protons. Both acids and bases are called protoliths.

2. Lewis acid and base theory . In it, an acid is any particle capable of accepting a pair of electrons, and a base is a particle capable of donating this pair. The Lewis theory is very similar to the theory Bronsted - Lowry, but differs from it in that it covers a wider range of compounds.

3. Usanovich's theory. In it, an acid is a particle that can split off cations, including a proton, or add anions, including an electron. A base is a particle that can accept a proton and other cations or donate an electron and other anions. .

Nomenclature:

Inorganic compounds containing -OH groups are called hydroxides. NaOH - sodium hydroxide, Fe(OH) 2 - iron(II) hydroxide, Ba(OH )2-barium hydroxide. (in brackets the valency of the element is indicated (if it is a variable))

For compounds containing oxygen, the names of hydroxides are used, with the prefix "meta": AlO (OH) - aluminum metahydroxide, Mn O(OH) - manganese metahydroxide

For oxides hydrated with an indefinite number of water molecules, Me 2 O n n H 2 O, it is illegal to write formulas like Me(OH)n . Calling such compounds hydroxides is also not recommended. Name examples: Tl 2 O 3 ∙n H 2 O - thallium(III) oxide polyhydrate, MnO 2∙nH2 O - manganese(IV) oxide polyhydrate

There are also hydrates -NH 3 ∙H 2 O (hydrate ammonia) \u003d NH 4 OH (ammonium hydroxide).

Bases give salts when interacting with acids (neutralization reaction), when interacting with acid oxide, amphoteric hydroxide, amphoteric metal, amphoteric oxide, non-metal.

NaOH+HCl→NaCl+H 2 O(neutralization reaction)

2NaOH+2NO 2 →NaNO 3 +NaNO 2 +H 2 O(reaction with mixed anhydride)

Cl 2 +2KOH→KCl+KClO+H 2 O(reaction proceeds without heating)

Cl 2 +6KOH→5KCl+KClO 3 +3H 2 O(reaction proceeds with heating)

3S+6NaOH→2Na 2 S+Na 2 SO 3 +3H 2 O

2Al+2NaOH+6H 2 O→2Na+3H 2

Al 2 O 3 + 6NaOH → 2Na 3 AlO 3 +3H 2 O

NaOH+Al(OH) 3 →Na

Methods for obtaining bases:

1. Interaction of alkali and alkaline earth metals, and ammonia with water. Metals (only alkali or alkaline earth), interacting with water form alkali and release hydrogen. Ammonia interacting with water forms an unstable compound NH 4OH:

2Na+2H 2 O→2NaOH+H 2

Ba+2H 2 O→ Ba ( Oh ) 2 +H 2

NH 3 +H 2 O↔NH 4 Oh

2. Direct attachment by basic oxides to water. Most basic oxides do not directly add water, only oxides of alkali metals (alkali metals) and alkaline earth metals (alkaline earth metals), attaching water, form bases:

Li 2 O+H 2 O→2LiOH

BaO+H 2 O→ Ba ( Oh ) 2

3. Salt interaction . This is one of the most common ways to obtain salts and bases. Since this is an ion exchange reaction, both reactants must be soluble, and one of the products must not:

NaOH+FeCl 3 →3NaCl+Fe(OH) 3 ↓

Na 3 PO 4 +3LiOH→3NaOH+Li 3 PO 4 ↓

4. Electrolysis of salt solutionsalkaline And alkaline earth metals .In the electrolysis of solutionssalt data metals neverare not released at the cathode (instead, hydrogen is released from water: and 2H 2 O-2e - \u003d H 2 ↓ + 2OH - ), and the halogen is reduced at the anode (all except F - ), or in the case of an oxygen-containing acid, the following reaction occurs:

2H 2 O-4e - =4H + +O 2 , halogens are reduced according to the scheme: 2X - -2e - =X 2 (where X is halogen)

2NaCl+2H 2 O→2NaOH+Cl 2 +H 2

An alkali accumulates in an aqueous solution, which can then be isolated by evaporating the solution.

This is interesting:

Peroxides and superoxides of alkali and alkaline earth metals react with water to form the corresponding hydroxide and hydrogen peroxide.

Na 2 O 2 +2 H 2 O →2 NaOH + H 2 O 2

4NaO 2 + 2 H 2 O →4 Na Oh + 3O 2

The Bronsted-Lowry theory makes it possible to quantify the strength of bases, that is, their ability to split off a proton from acids. This is usually done using the basicity constant K b . For example, for ammonia as a Bronsted base, one can write:

NH 3 + H 2 O ↔ NH 4 + +OH -

For a more convenient display of the basicity constants, a negative logarithm is used: pK b = -log K b . It is also logical that the strength of the bases increases in the series of metal stresses from right to left.

NaOH + C 2 H 5 Cl → NaCl + C 2 H 4 + H 2 O (a method for obtaining alkenes, ethylene (ethene) in this case), an alcohol solution of sodium hydroxide was used.

NaOH + C 2 H 5 Cl → NaCl + C 2 H 5 Oh (a method for obtaining alcohols, ethanol in this case), an aqueous solution of sodium hydroxide was used.

2 NaOH + C 2 H 5 Cl →2 NaCl + C 2 H 2 + H 2 O (a method for obtaining alkynes, acetylene (ethyne) in this case), an alcohol solution of sodium hydroxide was used.

C 6 H 5 Oh (phenol)+ NaOH → C 6 H 5 ONa + H 2 O

The product of substitution of one of the ammonia hydrogens for a hydroxyl group is hydroxylamine ( NH 2 Oh). It is formed during the electrolysis of nitric acid (with mercury or lead cathodes), as a result of its reduction by atomic hydrogen, which is formed as water is electrolyzed in parallel:

HNO 3 +6 H → NH 2 Oh +2 H 2 O

2 H 2 O → 2 H 2 + O 2

amphoteric hydroxides.

These compounds give salts both when interacting with acids (medium salts) and when interacting with bases (complex compounds). All amphoteric hydroxides are slightly soluble. Their dissociation can be considered both in terms of the basic and acidic types, but since these 2 processes occur simultaneously, the process can be written as follows (Me-metal):

Me x+ +xOH - ⇌ Me(OH) x ≡H x MeO x ⇌ xH + +MeO x x-

Since amphoteric hydroxides are hydrates of amphoteric oxides, their most prominent representatives are hydrates of the following oxides: ZnO, Al 2 O 3, BeO, SnO, PbO, Fe 2 O 3, Cr 2 O 3, MnO 2, TiO 2.

Reaction examples:

NaOH+Al(OH) 3 ↓→Na- sodium hydroxoalluminate

Al(OH) 3 ↓+3HCl→AlCl 3 +3H 2 O

But, knowing that amphoteric hydroxides also dissociate according to the acid type, one can write their interaction with alkalis using another equation:

Zn(OH) 2 ↓+2NaOH→Na 2 (in solution)

H 2 ZnO 2 ↓+2NaOH→Na 2 ZnO 2 +H 2 O(in melt)

1)H 3 AlO 3 ↓+3NaOH→Na 3 AlO 3 +3H 2 O(sodium orthoaluminate was formed here (the reaction took place in solution), but if the reaction occurs during fusion, sodium metaaluminate will be formed)

2) HAlO 2 +NaOH→NaAlO 2 +H 2 O(sodium metaaluminate was formed, which means that orthoaluminum and metaluminic acids entered into reactions 1 and 2, respectively)

Amphoteric hydroxides are usually obtained by the interaction of their salts with alkalis, the amount of which is accurately calculated according to the reaction equation:

3NaOH+ Cr(NO 3 ) 3 →3NaNO 3 +Cr(OH) 3 ↓

2NaOH+ Pb(CH 3 COO) 2 →2CH 3 COONa+Pb(OH) 2 ↓

Editor: Kharlamova Galina Nikolaevna

Bases (hydroxides) – complex substances, whose molecules in their composition have one or more OH hydroxyl groups. 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 that 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, litmus indicator - in Blue colour, and phenolphthalein becomes fuchsia.

2. React with acidic oxides 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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