Since d-metal oxides are insoluble in water, their hydroxides are obtained indirectly through exchange reactions between their salts and alkali solutions:

ZnCl 2 + 2NaOH \u003d Zn (OH) 2 + 2NaCl;

MnCl 2 + 2NaOH = Mn(OH) 2 + 2NaCl (in the absence of oxygen);

FeSO 4 + 2KOH \u003d Fe (OH) 2 + K 2 SO 4 (in the absence of oxygen).

Hydroxides of d-elements in the lowest oxidation states are weak bases; They are insoluble in water, but soluble in acids:

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

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

Hydroxides of d-elements in intermediate oxidation states and zinc hydroxide dissolve not only in acids, but also in excess alkali solutions with the formation of hydroxo complexes (i.e. they exhibit amphoteric properties), for example:

Zn(OH) 2 + H 2 SO 4 = ZnSO 4 + 2H 2 O;

Zn (OH) 2 + 2NaOH \u003d Na 2;

Cr(OH) 3 + 3HNO 3 = Cr(NO 3) 3 + 3H 2 O;

Cr(OH) 3 + 3KOH = K 3 .

In higher oxidation states, transition metals form hydroxides, which exhibit acidic properties or amphoteric properties with a predominance of acidic:

With an increase in the degree of oxidation of the element, the basic properties of oxides and hydroxides weaken, and the acid properties increase.

Therefore, along the period from left to right, there is an increase in the acidic properties of d-metal hydroxides in higher oxidation states to the Mn subgroup, then the acidic properties weaken:

Sc(OH) 3 - TiO 2 xH 2 O - V 2 O 5 xH 2 O - H 2 CrO 4 - HMnO 4

Strengthening acidic properties

Fe(OH) 3 - Co(OH) 2 - Cu(OH) 2 - Zn(OH) 2

Slow weakening of acidic properties

Consider the change in the properties of d-metal hydroxides in subgroups. From top to bottom in the subgroup, the basic properties of hydroxides of d-elements in higher oxidation states increase, acidic properties decrease. For example, for the sixth group of d-metals:

H 2 CrO 4 - sharply - MoO 3 H 2 O - weakly - WO 3 H 2 O

Acid properties decrease

Redox properties of compounds of d-elements

Connections of d - elements in lower oxidation states they show mostly, reducing properties, especially in an alkaline environment. Therefore, for example, the hydroxides Mn(+2), Cr(+2), Fe(+2) are very unstable and are quickly oxidized by atmospheric oxygen:

2Mn(OH)2 + O2 + 2H2O = 2Mn(OH)4;

4Cr(OH) 2 + O 2 + 2H 2 O = 4Cr(OH) 3

In order to convert cobalt (II) or nickel (II) hydroxide into Co (OH) 3 or Ni (OH) 3, it is necessary to use a stronger oxidizing agent - for example, hydrogen peroxide H 2 O 2 in an alkaline medium or bromine Br 2:

2Co(OH) 2 + H 2 O 2 = 2Co(OH) 3;

2 Ni(OH) 2 + Br 2 +2NaOH = 2 Ni(OH) 3 + 2NaBr

Ti(III), V(III), V(II), Cr(II) derivatives are easily oxidized in air, some salts can be oxidized even with water:

2Ti 2 (SO 4) 3 + O 2 + 2H 2 O \u003d 4TiOSO 4 + 2H 2 SO 4;

2CrCl 2 + 2H 2 O \u003d 2Cr (OH) Cl 2 + H 2

Compounds of d-elements in higher oxidation states (from +4 to +7) usually exhibit oxidizing properties. However, Ti (IV) and V (V) compounds are always stable and therefore have relatively weak oxidizing properties:

TiOSO 4 + Zn + H 2 SO 4 = Ti 2 (SO 4) 3 + ZnSO 4 + H 2 O;

Na 3 VO 4 + Zn + H 2 SO 4 = VOSO 4 + ZnSO 4 + H 2 O

The recovery takes place under harsh conditions - with atomic hydrogen at the time of its release (Zn + 2H + = 2H+ + Zn 2+).

And chromium compounds in higher oxidation states are strong oxidizing agents, especially in an acidic environment:

K2Cr2O7 + 3SO2 + H2SO4 = Cr2(SO4)3 + K2SO4 + H2O;

2CrO 3 + C 2 H 5 OH \u003d Cr 2 O 3 + CH 3 COH + H 2 O

Mn(VI), Mn(VII), and Fe(VI) compounds exhibit even stronger oxidizing properties:

2KMnO 4 + 6KI + 4H 2 O = 2MnO 2 + 3I 2 + 8KOH;

4K 2 FeO 4 + 10H 2 SO 4 \u003d 2Fe 2 (SO 4) 3 + 3O 2 + 10H 2 O + 4K 2 SO 4

In this way, the oxidizing properties of compounds of d-elements in higher oxidation states increase from left to right over the period.

The oxidizing ability of compounds of d-elements in higher oxidation states in a subgroup from top to bottom weakens. For example, in the chromium subgroup: potassium dichromate K 2 Cr 2 O 7 interacts even with such a weak reducing agent as SO 2. To restore molybdate or tungstate ions, a very strong reducing agent is needed, for example, a hydrochloric acid solution of tin (II) chloride:

K 2 Cr 2 O 7 + SO 2 + H 2 SO 4 = Cr 2 (SO 4) 3 + K 2 SO 4 + H 2 O

3 (NH 4) 2 MoO 4 + НSnCl 3 + 9HCl = MoO 3 MoO 5 + H 2 SnCl 6 + 4H 2 O + 6NH 4 Cl

The last reaction occurs when heated, and the oxidation state of the d-element decreases very slightly.

Compounds of d-metals in an intermediate oxidation state have redox duality. For example, iron (III) compounds, depending on the nature of the partner substance, can exhibit the properties of a reducing agent:

2FeCl3 + Br2 + 16KOH = 2K2FeO4 + 6KBr + 6KCl + 8H2O,

and oxidizing properties:

2FeCl 3 + 2KI = 2FeCl 2 + I 2 + 2KCl.

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

base acid salt

Cu(OH) 2 + H 2 SO 4 = CuSO 4 + 2H 2 O,

base acid salt

2NaOH + PbO \u003d Na 2 PbO 2 + H 2 O,

base amphoteric salt

2NaOH + Pb(OH) 2 = Na 2 PbO 2 + 2H 2 O,

base amphoteric salt

hydroxide

2H 3 PO 4 + 3Na 2 O \u003d 2Na 3 PO 4 + 3H 2 O,

acid base salt

H 2 SO 4 + SnO \u003d SnSO 4 + H 2 O,

acid amphoteric salt

H 2 SO 4 + Sn (OH) 2 \u003d SnSO 4 + 2H 2 O.

acid amphoteric salt

hydroxide

Amphoteric hydroxides in reactions with acids exhibit the main properties:

2Al (OH) 3 + 3H 2 SO 4 \u003d Al 2 (SO 4) 3 + 6H 2 O,

with alkalis (bases) - acidic properties:

H 3 AlO 3 + 3NaOH \u003d Na 3 AlO 3 + 3H 2 O,

or H 3 AlO 3 + NaOH = NaAlO 2 + 2H 2 O.

Bases and acids react with salts if the result is a precipitate or a weak electrolyte. Weak acids - H 3 PO 4, H 2 CO 3, H 2 SO 3, H 2 SiO 3 and others.

2NaOH + NiSO 4 \u003d Ni (OH) 2  + Na 2 SO 4,

salt base

3H 2 SO 4 + 2Na 3 PO 4 = 2H 3 PO 4 + 3Na 2 SO 4

acid salt

Anoxic acids enter into the same reactions as the previously considered oxygen-containing acids.

Example. Make formulas of hydroxides corresponding to oxides: a) FeO; b) N 2 O 3; c) Cr 2 O 3 . Name the connections.

Solution

a) FeO is the basic oxide, therefore, the corresponding hydroxide is the base, in the base formula the number of hydroxo groups (OH) is equal to the oxidation state of the metal atom; the formula of iron (II) hydroxide is Fe (OH) 2.

b) N 2 O 3 is an acid oxide, therefore, the corresponding hydroxide is an acid. The formula of an acid can be obtained from the representation of the acid as a hydrate of the corresponding oxide:

N 2 O 3 . H 2 O \u003d (H 2 N 2 O 4) \u003d 2HNO 2 - nitrous acid.

c) Cr 2 O 3 is an amphoteric oxide, therefore, the corresponding hydroxide is amphoteric. Amphoteric hydroxides are written in the form of bases - Cr (OH) 3 - chromium (III) hydroxide.

salt

salt- substances that consist of basic and acidic residues. Thus, the salt CuSO 4 consists of the main residue - the metal cation Cu 2+ and the acid residue - SO 4 2 .

According to the traditional nomenclature, the names of salts of oxygen acids are as follows: the ending is added to the root of the Latin name of the central atom of the acid residue - at(at higher oxidation states of the central atom) or - it(for a lower oxidation state) and then - the remainder of the base in the genitive case, for example: Na 3 PO 4 - sodium phosphate, BaSO 4 - barium sulfate, BaSO 3 - barium sulfite. The names of salts of oxygen-free acids are formed by adding the suffix to the root of the Latin name of the non-metal - id and the Russian name for the metal (residue from the base), for example CaS - calcium sulfide.

Medium salts do not contain in its composition, hydrogen ions and hydroxo groups capable of being replaced by metal, for example CuCl 2 , Na 2 CO 3 and others.

Chemical properties of salts

Medium salts enter into exchange reactions with alkalis, acids, salts. See above for examples of relevant reactions.

Acid salts contain as part of the acid residue, a hydrogen ion, for example NaHCO 3, CaHPO 4, NaH 2 PO 4, etc. In the name of an acid salt, the hydrogen ion is denoted by the prefix hydro-, before which indicate the number of hydrogen atoms in the salt molecule, if it is greater than one. For example, the names of the salts of the above composition, respectively, are sodium bicarbonate, calcium hydrogen phosphate, sodium dihydrogen phosphate.

Acid salts are

the interaction of the base and polybasic acid with an excess of acid:

Ca(OH) 2 + H 3 PO 4 = CaHPO 4 + 2H 2 O;

the interaction of the average salt of a polybasic acid and the corresponding acid or a stronger acid taken in deficiency:

CaCO 3 + H 2 CO 3 \u003d Ca (HCO 3) 2,

Na 3 PO 4 + HCl = Na 2 HPO 4 + NaCl.

Basic salts contain as part of the rest of the base, a hydroxo group, for example CuOHNO 3, Fe (OH) 2 Cl. In the name of the basic salt, the hydroxo group is denoted by the prefix hydroxo-, for example, the names of the above salts, respectively: copper (II) hydroxonitrate, iron (III) dihydroxochloride.

Basic salts are

the interaction of a polyacid (containing more than one hydroxo group in its composition) base and acid with an excess of base:

Cu(OH) 2 + HNO 3 = CuOHNO 3 + H 2 O;

the interaction of a salt formed by a polyacid base and a base taken in deficiency:

FeCl 3 + NaOH = FeOHCl 2  + NaCl,

FeCl 3 + 2NaOH \u003d Fe (OH) 2 Cl + 2NaCl.

Acid and basic salts have all the properties of salts. In reactions with alkalis, acid salts, and with acids, basic salts turn into medium ones.

Na 2 HPO 4 + NaOH = Na 3 PO 4 + H 2 O,

Na 2 HPO 4 + 2HCl \u003d H 3 PO 4 + 2NaCl,

FeOHCl 2 + HCl \u003d FeCl 3 + H 2 O,

FeOHCl 2 + 2NaOH \u003d Fe (OH) 3  + 2NaCl.

Example 1. Make formulas for all salts that can be formed by the base Mg (OH) 2 and the acid H 2 SO 4.

Solution

Salt formulas are composed of possible basic and acidic residues, observing the rule of electrical neutrality. Possible basic residues are Mg 2+ and MgOH +, acidic residues are SO 4 2- and HSO 4 -. The charges of complex basic and acid residues are equal to the sum of the oxidation states of their constituent atoms. By combining basic and acidic residues, we draw up the formulas of possible salts: MgSO 4 - average salt - magnesium sulfate; Mg (HSO 4) 2 - acid salt - magnesium hydrosulfate; (MgOH) 2 SO 4 - the main salt is magnesium hydroxosulfate.

Example 2 Write the reactions of salt formation during the interaction of oxides

a) PbO and N 2 O 5; b) PbO and Na 2 O.

Solution

In reactions between oxides, salts are formed, the main residues of which are formed from basic oxides, the acid residues from acid oxides.

a) In the reaction with the acidic oxide N 2 O 5, the amphoteric oxide PbO exhibits the properties of the basic oxide, therefore, the main residue of the resulting salt is Pb 2+ (the charge of the lead cation is equal to the oxidation state of lead in the oxide), the acid residue is NO 3  (acid residue corresponding to a given acidic nitric acid oxide). Reaction equation

PbO + N 2 O 5 \u003d Pb (NO 3) 2.

b) In the reaction with the basic oxide Na 2 O, the amphoteric oxide PbO exhibits the properties of an acid oxide, the acid residue of the resulting salt (PbO 2 2 -) is found from the acid form of the corresponding amphoteric hydroxide Pb (OH) 2 \u003d H 2 PbO 2. Reaction equation

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 give specific examples. The aluminum base belongs to amphoteric hydroxides, the properties of which we will consider in the article. The obligatory presence in the base molecules of a hydroxyl group associated with the metal cation by an ionic bond type can be determined using indicators, for example, 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 valence.

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 are destroyed under the action of high temperature, forming 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 the special properties of amphoteric hydroxides. 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 that requires 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 making soap, processing natural leather, as well as in technologies for the production of rayon and paper.

DEFINITION

Hydroxides complex substances are called, which include metal atoms connected to one or more hydroxo groups.

Most bases are solids with varying solubility in water. Copper (II) hydroxide is blue (Fig. 1), iron (III) hydroxide is brown, most of the others are white.

Rice. 1. Copper (II) hydroxide. Appearance.

Obtaining hydroxides

Soluble bases (alkalis) in the laboratory can be obtained by the interaction of active metals and their oxides with water:

CaO + H 2 O \u003d Ca (OH) 2.

The alkalis sodium hydroxide and calcium hydroxide are obtained by electrolysis of aqueous solutions of sodium chloride and potassium chloride.

Water-insoluble bases are obtained by the reaction of salts with alkalis in aqueous solutions:

FeCl 3 + 3NaOH aq \u003d Fe (OH) 3 ↓ + 3NaCl.

Chemical properties of hydroxides

Soluble and insoluble bases have a common property: they react with acids to form salts and water (neutralization reaction):

NaOH + HCl \u003d NaCl + H 2 O;

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

Alkali solutions change the color of some substances - litmus, phenolphthalein and methyl orange, called indicators (Table 1).

Table 1. Color change of indicators under the influence of solutions of acids and bases.

In addition to the general properties, alkalis and water-insoluble bases also have specific ones. For example, when a blue precipitate of copper (II) hydroxide is heated, a black substance is formed - this is copper (II) oxide:

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

Alkalis, unlike insoluble bases, usually do not decompose when heated. Their solutions act on indicators, corrode organic substances, react with salt solutions (if they contain a metal capable of forming an insoluble base) and acid oxides:

Fe 2 (SO 4) 3 + 6KOH \u003d 2Fe (OH) 3 ↓ + 3K 2 SO 4;

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

Application of hydroxides

Hydroxides are widely used in industry and everyday life. For example, calcium hydroxide is of great importance. It is a white loose powder. When mixed with water, the so-called milk of lime is formed. Since calcium hydroxide is slightly soluble in water, after filtering the milk of lime, a clear solution is obtained - lime water, which becomes cloudy when carbon dioxide is passed through it. Slaked lime is used to prepare the Bordeaux mixture - a means of combating plant diseases and pests. Lime milk is widely used in the chemical industry, for example, in the production of sugar, soda and other substances.

Sodium hydroxide is used for oil refining, soap production, and in the textile industry. Potassium hydroxide and lithium hydroxide are used in batteries.

Examples of problem solving

EXAMPLE 1

EXAMPLE 2

oxides - These are complex substances consisting of some element and oxygen with an oxidation state -2.

For example: K2O, CaO, Fe2O3, CO2, P2O5, SO3, Cl2O7, OsO4. Oxides form all chemical elements, except He, Ne, Ar. The chemical bond between oxygen and another element is either ionic or covalent. According to their chemical properties, oxides are divided into salt-forming and non-salt-forming. The latter include, for example, N2O, NO, NO 2 , SiO, SO.

Salt-forming oxides are divided into basic, acidic and amphoteric.

Basic oxides. Oxides whose hydrates are bases are called basic oxides. For example, Na2O, CuO are basic oxides, since the bases NaOH, Cu(OH)2 correspond to which. As a rule, the basic oxides can be oxides of metals with an oxidation state of +1, +2. The chemical bond here is ionic.

Oxides of alkaline (Li, Na, K, Rb, Cs, Fr) and alkaline earth metals (Ca, Sr, Ba, Ra), interacting with water, give bases. For example:

K2O + H2O = 2KOH

BaO + H2O = Ba(OH)2

The remaining basic oxides practically do not interact with water. Basic oxides react with acids and give salt and water:

Fe 2 O 3 + 3H 2 SO 4 \u003d Fe 2 (SO 4) 3 + 3H 2 O

Fe 2 O 3 + 6H + = 2Fe 3 + + 3H 2 O

Basic oxides react with acidic oxides and give salts:

FeO + SiO 2 \u003d FeSiO 3 (t)

Acidic oxides. Oxides whose hydrates are acids are called acidic. Acid oxides include non-metal and metal oxides with an oxidation state of +4, +5, +6, +7. For example, N 2 O 3, P 2 O 5 , CrO 3 , Mn 2 O 7, CO 2, V 2 O 5, SO 3, Cl 2 O 7 - acid oxides, since the corresponding acids are HNO 2, H 3 PO 4, H 2 CrO 4, HMnO 4, etc. (the chemical bond here is covalent and ionic). Most acidic oxides react with water and form acids. For example:

SO 3 + H2O = H2SO4

Мn2O7 + H2O = 2HMnO4

SiO2 + H2O ≠

Acid oxides react with bases (alkalis) and give salt and water:

N 2 O 5 + Ca (OH) 2 \u003d Ca (NO 3) 2 + H 2 O

N 2 O 5 + 2OH‾ = 2NO 3 ‾ + H 2 O

Amphoteric oxides. Metal oxides with an oxidation state of +3, +4 and sometimes +2, which, depending on the environment, exhibit basic or acidic properties, that is, react with acids and bases, are called amphoteric. They correspond to hydrates, acids and bases. For example:

Zn(OH)2 ← ZnO → H2ZnO2

H2O Al(OH) 3 ← Al 2 O 3 → H 3 AlO 3 → HalO 2

Amphoteric oxides react with acids and bases:

Al2Oz + 3H2SO4 = Al2 (SO4)3 + 3H2O

Al2Oz + 6H + = 2Al 3+ + 3H2O

Al2Oz + 2NaOH + 3H2O = 2Na

Al2Oz + 2OH‾ + 3H2O = 2[Al(OH)4]‾

When Al2O3 is fused with alkalis, metaaluminates are formed:

fusion of Al2O3 + 2NaOH → 2NaAlO2 + H2O

sodium metaaluminate

Al2Oz + 2OH‾ = 2Al O2‾ + H2O

Amphoteric oxides do not combine directly with water.

Hydroxides

Chemical compounds with general formulaR(Oh) ncalled hydroxides, whereR - an atom or group of atoms with a positive charge.

Depending on the type of electrolytic dissociation, hydroxides are divided into three groups: bases, acids, and amphoteric hydroxides. For example:

Ba(OH)2 ↔ Ba 2 + + 2OH‾ base

H2SO4 ↔ 2H + + SO2 2 ‾ acid

Pb 2 + + 2OH‾ ↔ Pb(OH)2 ↔2H + + PbO2 2 ‾ amphoteric hydroxide