The oxide does not dissolve in water. Advances of modern natural science. Chemical interactions for the class of medium salts

The complication of the structure of a substance when classifying inorganic compounds occurs in the following sequence: elements ® oxides (basic, acidic, amphoteric) ® hydroxides (bases and acids) ® salts (average, acidic, basic).

Oxides are called complex substances consisting of two elements, one of which is oxygen. According to their chemical nature, oxides are divided into three groups:

· basic oxides, Na 2 O, MgO, CaO, FeO, NiO, Fe 2 O 3, ...;

· acid oxides, SO 2, SO 3, CO 2, Mn 2 O 7, P 2 O 5, ...;

· amphoteric oxides, Al 2 O 3, ZnO, BeO, SnO, Cr 2 O 3, PbO

solid oxides K 2 O, Al 2 O 3, P 2 O 5, ...

liquid: SO 3, N 2 O 4, ...

gaseous: CO 2, NO 2, SO 2 ...

Based on solubility in water, oxides are divided:

on soluble(SO 2, CO 2, K 2 O, Na 2 O, Rb 2 O, CaO)

And insoluble: ( CuO, FeO, NiO, SiO 2, Al 2 O 3, MoO 3, amphoteric oxides)

1.1.1 Basic oxides

Mainare called oxides, which when reacting with acids form salt and water. The main oxides include potassium oxide K2O, calcium oxide CaO, manganese(II) oxide MnO, copper(I) oxide Cu2O, etc.

Basic oxides react with acids to form

salt and water; MnO + 2HCl Þ MnCl 2 + H 2 O; Fe 2 O 3 + 3H 2 SO 4 = Fe 2 (SO 4) 3 + 3H 2 O.

Basic oxides interact with acidic oxides with

the formation of salts: CaO + CO 2 = CaCO 3; 3Na 2 O + P 2 O 5 = 2Na 3 PO 4.

2FeO + SiO 2 = Fe 2 SiO 4

Oxides of alkali and alkaline earth metals react with water:

K 2 O + H 2 O = 2KOH; CaO + H 2 O + Ca(OH) 2

One can also define basic oxides as those oxides to which bases correspond. For example, manganese oxide MnO corresponds to hydroxide Mn(OH) 2. The main oxides are oxides s-, f- And d-elements in the lowest oxidation state and oxides of some p-elements.

Acidic oxides

Acidic oxides can be called oxides, which correspond to acids. Thus, sulfur oxide (VI) SO 3 corresponds to sulfuric acid H 2 SO 4, higher manganese oxide (VII) Mn 2 O 7 - manganese acid HMnO 4.

(A). A common property of all acidic oxides is their ability to react with bases to form salt and water:

CO 2 + 2NaOH = Na 2 CO 3 + H 2 O to write the formula of the salt you need to know

Which acid corresponds to this oxide?

N 2 O 5 + Ba(OH) 2 = Ba(NO 3) 2 + H 2 O; SO 3 + Ca(OH) 2 = CaSO 4 + H 2 O

[ HNO3]

(b). Acidic oxides interact with basic oxides to form salts: CaO + CO 2 = CaCO 3 ; 3Na 2 O + P 2 O 5 = 2Na 3 PO 4.

(V). In relation to water, acid oxides can be well or poorly soluble. Soluble oxides include carbon monoxide (IV) CO 2, sulfur oxides, etc. Poorly soluble acidic oxides include silicon oxide SiO 2, molybdenum oxide MoO 3, etc. When dissolved in water, acids are formed: CO 2 + H 2 O = H 2 CO 3; SO 3 + H 2 O = H 2 SO 4

3

1 Moscow State Technical University named after. N.E. Bauman

2 First Moscow State Medical University named after. THEM. Sechenov

3 Moscow Pedagogical State University

The issues of etching oxide deposits from the surface of steels containing cobalt and iron have always been of practical importance and have been relevant. Having studied a large amount of material on this issue, the authors state that some aspects of the problem have not yet been fully studied (these include the influence of the characteristics of electrolyte solutions, identifying the mechanism of action of these factors). Cobalt and iron oxides are widely used as catalysts for various chemical processes (oxidation of methane and carbon monoxide, dehydrogenation of paraffins, etc.). Their properties depend on the characteristics of the surface, which determines the kinetics of oxide dissolution. Experimental studies conducted on the effect of mineral acids (in particular, H2SO4) on the rate of heterogeneous reaction (Co3O4 and Fe3O4 in an acidic medium) revealed the nature of the limiting stage, which consists in the formation of surface compounds of the type - and their subsequent transition to the electrolyte solution. A systematic analysis of oxide dissolution curves has also been developed to calculate kinetic parameters: activation energy and reaction orders for hydrogen ions and sulfate ions.

cobalt oxide

iron oxide

kinetics

dissolution

modeling

Barton–Stransky model

Hougen–Watson method

1. Bokshtein B.S., Mendelev M.I., Pokhvisnev Yu.V. Physical chemistry: thermodynamics and kinetics. – M.: Publishing house “MISIS”, 2012. – 258 p.

2. Butler J. Ionic equilibria. – L.: Chemistry, 1973. – 448 p.

3. Delmon B. Kinetics of heterogeneous reactions. – M.: Mir, 1972. – 555 p.

4. Barre P. Kinetics of heterogeneous processes. – M.: Mir, 1976. – 400 p.

5. Kiselev M.Yu. Mechanism and kinetics of pyrite dissolution by electrochemical chlorination // News of higher educational institutions. Mining magazine. – 2010. – No. 4. – P. 101–104.

6. Korzenshtein N.M., Samuylov E.V. Volumetric condensation in heterogeneous reactions // Colloid Journal. – 2013. – T. 75, No. 1. – 84 p.

7. Kolesnikov V.A., Kapustin V.A., Kapustin Yu.I., Isaev M.K., Kolesnikov A.V. Metal oxides – promising materials for electrochemical processes // Glass and Ceramics. – 2016. – No. 12. – P. 23–28.

8. Yakusheva E.A., Gorichev I.G., Atanasyan T.K., Izotov A.D. Study of the kinetics of dissolution of cobalt oxides (Co3O4, Co2O3) at various concentrations of H2SO4, HCl, EDTA and pH // Volgograd: Abstracts of XIX Mend. Congress on General and Applied Chemistry. – 2011. – T. 3 – P. 366.

9. Yakusheva E.A., Gorichev I.G., Atanasyan T.K., Layner Yu.A. Kinetics of dissolution of cobalt oxides in acidic media // Metals. – 2010. – No. 2. – P. 21–27.

10. Yakusheva E.A., Gorichev I.G., Atanasyan T.K., Plakhotnaya O.N., Goryacheva V.N. Modeling of kinetic processes of dissolution of cobalt and copper oxides in sulfuric acid // Bulletin of MSTU im. N.E. Bauman. Ser. Natural Sciences. – 2017. – No. 3. – pp. 124–134.

The conducted experimental studies of the dissolution of oxide phases make it possible to describe in detail the processes of the behavior of the solid phase in an acidic environment, to explain the phenomena occurring on the surface of oxides, taking into account their acid-base characteristics and the dissolution mechanism, to carry out modeling of topo chemical reactions.

Purpose of the study consists of studying and modeling the process of dissolution of Co3O4 and Fe3O4 in sulfuric acid.

Materials and research methods

For research, samples weighing 500 mg with d = 80÷100 µm were taken. Identification of oxides was carried out by X-ray diffraction, IR and thermal analyses.

To elucidate the mechanism of dissolution of solid samples of metal oxides in acidic media, the experiment was carried out in an instrument (a thermostated reactor with a volume of 0.5 l) to study the kinetics of dissolution of solid samples, excluding the influence of any uncontrolled factors on the phenomenon being studied. The experimental temperature was 363 K. The experiment was carried out at various pH values ​​and concentrations of mineral acid.

At certain time intervals, samples of the liquid phase were taken from the reaction vessel using a glass Schott filter. The concentration of cobalt ions was determined spectrophotometrically (UF-3100 spectrophotometer) using ammonium thiocyanate, and iron - using o-phenanthroline.

The obtained experimental data on the effect of acid concentration on the rate of dissolution of cobalt oxide Co3O4 and Fe3O4 are presented in Fig. 1 (dots - experimental data, lines - simulation results). The solute fraction a was calculated using the equation: a = Dt/D∞.

Rice. 1. a) dependence of the proportion of dissolved Co3O4 oxide on time at different concentrations of sulfuric acid (mol/l): 1 - 10.0; 2 - 5.93; 3 - 2.97; 4 - 1.0; 5 - 0.57; 6 - 0.12; T = 363.2 K; b) dependence of the proportion of dissolved Fe3O4 oxide on time at different concentrations of sulfuric acid (mol/l): 1 - 10.3; 2 - 7.82; 3 - 3.86; 4 - 2.44; T = 293 K

Research results and discussion

Calculation of kinetic parameters. An analysis of experimental kinetic data was carried out using the equations of heterogeneous kinetics, which made it possible to determine the orders of reactions for various ions (ni), the specific rate of dissolution (Wi), its dependence on the concentration of the solution, as well as the activation energies of reactions (Ea).

The kinetics of heterogeneous reactions is based on the mandatory consideration of changes in the surface of particles during the dissolution process over time; in addition, as a rule, heterogeneous reactions are characterized by a constant rate over time (1).

In this case, the rate of oxide dissolution can be represented by the equation:

where Wi is the specific dissolution rate; f(α) is a function that takes into account how the oxide surface changes over time.

To clarify the mechanism of dissolution and model this phenomenon, we used the Barton-Stransky model (2):

, (2)

where A is a constant. Its value is directly proportional to the number of active centers on the surface of one oxide particle.

To find the values ​​of the variables W and A, nonlinear regression analysis methods and the MathCad computer program were used.

Table 1

Specific rate of dissolution of oxides Co3O4 and Fe3O4 depending on the concentration of H2SO4

From the data in the table and Fig. 2 (dots - experimental data, lines - the result of modeling according to equation (3)) it follows that cobalt oxide Co3O4 dissolves faster in sulfuric acid than iron oxide Fe3O4. The reaction order in terms of hydrogen ions for the two oxides is approximately 0.5. (all results are based on the Barton-Stransky model).

Rice. 2. a) dependence of the logarithm of speed (log W) on the logarithm of concentration (log C(H2SO4)) when dissolving Co3O4 in sulfuric acid; b) dependence of the logarithm of speed (log W) on the logarithm of concentration (log C(H2SO4)) when Fe3O4 is dissolved in sulfuric acid

The data obtained make it possible to describe the relationship between the specific dissolution rate of Co3O4 and Fe3O4 oxides and the H2SO4 concentration by the generalized equation

, (3)

where ≡, W0 is the dissolution rate constant, K1, K2 are constants.

Modeling the mechanism of dissolution of cobalt and iron oxides in inorganic acid. The dissolution of oxides in acids occurs on surface defects of the crystal lattice, the so-called active centers of oxide dissolution that have adsorbed H+ ions and H+...A- ion pairs.

The Hougen-Watson method makes it possible to simulate the effect of pH and acid concentration on the rate of dissolution of oxides.

In this case, the dissolution rate of cobalt and iron oxides will be expressed by the equation:

Presumably, particles of metal hydroxo complexes of the same composition as those present in the solution are formed on the surface of the oxides. To calculate the concentration of hydroxo complexes, we used material balance equations in hydrolysis reactions for hydrogen, cobalt and iron ions; hydrolysis equations for all stages to calculate hydrolysis constants. The Hougen-Watson method assumes that the dependence of the ion concentration on the surface of the oxides and in the solution obeys the Langmuir isotherm, which makes it possible to relate the surface and volume concentrations of ions (equation (5)).

The dependence of the specific dissolution rate of cobalt oxides Co3O4 and Fe3O4 in dilute sulfuric acid is expressed by equations (5-7).

The concentration of ions and can be expressed in terms of the total concentration of Co3+ and Fe3+ ions, if their content in the solution is established. In this case and . Then the speed is

If we simulate the process of oxide dissolution and assume that the ions act as surface-active particles, then the dependence of the process speed on the ion concentration will look as follows (a1 is the number of ions in the solution).

increase

solubility of oxides and

hydroxides

Subgroup

When dissolving, ionic oxides enter into a chemical interaction with water, forming the corresponding hydroxides:

Na 2 O + H 2 O → 2NaOH

CaO + H 2 O → Ca(OH) 2

very strong

basic oxide base

Hydroxides of alkali and alkaline earth metals are strong bases and completely dissociate in water into metal cations and hydroxide ions:

NaOH Na + + OH –

Since the concentration of OH - ions increases, solutions of these substances have a highly alkaline environment (pH>>7); they are called alkalis.

Second group highly soluble in water oxides and their corresponding hydroxy compounds – molecular oxides and acids with covalent type of chemical bonds. These include compounds of typical nonmetals in the highest oxidation state and some d-metals in the oxidation state: +6, +7. Soluble molecular oxides (SO 3 , N 2 O 5 , Cl 2 O 7 , Mn 2 O 7 ) react with water to form the corresponding acids:

SO 3 + H 2 O H 2 SO 4

sulfur oxide (VI) sulfuric acid

strong acid strong acid

N2O5 + H2O2HNO3

nitric oxide (V) nitric acid

Mn 2 O 7 + H 2 O 2HMnO 4

manganese(VII) oxide manganese acid

Strong acids (H 2 SO 4, HNO 3, HClO 4, HClO 3, HMnO 4) in solutions completely dissociate into H + cations and acid residues:

Stage 2: H 2 PO 4 – H + + HPO 4 2–

K 2 =(=6.2∙10 –8;

Stage 3: HPO 4 2– H + + PO 4 3–

K 3 =()/=4.4∙10 –13 ,

where K1, K2, K3 are the dissociation constants of orthophosphoric acid, respectively, for the first, second and third stages.

The dissociation constant (Appendix Table 1) characterizes the strength of the acid, i.e. its ability to decompose (dissociate) into ions in a given solvent at a given temperature. The greater the dissociation constant, the more the equilibrium is shifted towards the formation of ions, the stronger the acid, i.e. In the first stage, the dissociation of phosphoric acid is better than in the second and, accordingly, in the third stage.

Moderately soluble oxides of sulfur (IV), carbon (IV), nitrogen (III), etc. form corresponding weak acids in water, which partially dissociate.

CO 2 + H 2 O H 2 CO 3 H + + HCO 3 –

SO 2 + H 2 O H 2 SO 3 H + + HSO 3 –

N 2 O 3 + H 2 O 2HNO 2 H + + NO 2 –

weak-weak

acidic acids

Neutralization reaction

The neutralization reaction can be expressed by the following scheme:

H 2 O

(base or (acid or acids-

basic oxide)

5.3.1. Properties of basic compounds exhibit oxides and hydroxides of s-metals (exception Be), d-metals in the oxidation state (+1, +2) (exception Zn), some p-metals (see Fig. 3).

										VIIIA
I A	II A				IIIA	IVA	V.A.	VIA	VIIA
Li	Be				B	C	N	O	F

Diagonal similarity Al Zn Ge Insoluble: usually basic Amphoteric oxides Weak acid Oxides dissolve to form acids

Rice. 3. Acid-base properties of oxides and their corresponding hydroxy compounds

A characteristic property of basic compounds is their ability to react with acids, acidic or amphoteric oxides to form salts, for example:

KOH + HCl KCl + H 2 O

Ba(OH) 2 + CO 2 BaCO 3 + H 2 O

2NaO + Al 2 O 3 2NaAlO 2 + H 2 O

Depending on the number of protons that can be added to the base, there are monoacid bases (for example, LiOH, KOH, NH 4 OH), diacid bases, etc.

For polyacid bases, the neutralization reaction can proceed in stages with the formation of first basic and then intermediate salts.

Me(OH) 2 MeOHCl MeCl 2

hydroxide NaOH basic NaOH medium

metal salt salt

For example:

Stage 1: Co(OH) 2 + HCl CoOHCl + H 2 O

hydroxocobalt(II)

(basic salt)

Stage 2: Co(OH)Cl + HCl CoCl 2 + H 2 O

cobalt(II)

(medium salt)

5.3.2. Properties of acid compounds exhibit oxides and acids of nonmetals, as well as d-metals in the oxidation state (+5, +6, +7) (see Fig. 3).

A characteristic property is their ability to interact with bases, basic and amphoteric oxides to form salts, for example:

2HNO 3 + Cu(OH) 2 → Cu(NO 3) 2 + 2H 2 O

2HCl + CaO → CaCl 2 + H 2 O

H 2 SO 4 + ZnO → ZnSO 4 + H 2 O

CrO 3 + 2NaOH → Na 2 CrO 4 + H 2 O

Based on the presence of oxygen in their composition, acids are divided into oxygen-containing(for example, H 2 SO 4, HNO 3) and oxygen-free(HBr, H 2 S). Based on the number of hydrogen atoms contained in an acid molecule that can be replaced by metal atoms, there are monobasic acids (for example, hydrogen chloride HCl, nitrous acid HNO 2), dibasic (sulphurous H 2 SO 3, coal H 2 CO 3), tribasic (orthophosphoric H 3 PO 4) etc.

Polybasic acids are neutralized stepwise with the formation of initially acidic and then medium salts:

H 2 X NaHX Na 2 X

polybasic acidic medium

acid salt salt

For example, orthophosphoric acid can form three types of salts depending on the quantitative ratio of the acid and alkali taken:

a) NaOH + H 3 PO 4 → NaH 2 PO 4 + H 2 O;

1:1 dihydrogen phosphate

b) 2NaOH + H 3 PO 4 → Na 2 HPO 4 + 2H 2 O;

2:1 hydrogen phosphate

c) 3NaOH + H 3 PO 4 → Na 3 PO 4 + 3H 2 O.

3:1 orthophosphate

5.3.3. Amphoteric oxides and hydroxides form Be, p-metals located near the “amphoteric diagonal” (Al, Ga, Sn, Pb), as well as d-metals in oxidation states (+3, +4) and Zn (+2) (see Fig. 3 ).

Slightly dissolving, amphoteric hydroxides dissociate both basic and acidic:

2H + + 2– Zn(OH) 2 Zn 2+ + 2OH –

Therefore, amphoteric oxides and hydroxides can react with both acids and bases. When interacting with stronger acids, amphoteric compounds exhibit the properties of bases.

ZnO + SO 3 → ZnSO 4 + H 2 O

acid

Zn(OH) 2 + H 2 SO 4 → ZnSO 4 + H 2 O

basic acid

connections

When interacting with strong bases, amphoteric compounds exhibit the properties of acids, forming the corresponding salts. The composition of the salt depends on the reaction conditions. When fused, simple “dehydrated” salts are formed.

2NaOH + Zn(OH) 2 → Na 2 ZnO 2 + H 2 O

acid base sodium zincate

compound

2NaOH + ZnO → Na 2 ZnO 2 + H 2 O

Complex salts are formed in aqueous solutions of alkalis:

2NaOH + Zn(OH) 2 → Na 2

(aqueous tetrahydroxozincate

Modern chemical science represents many different branches, and each of them, in addition to its theoretical basis, has great applied and practical significance. Whatever you touch, everything around you is a chemical product. The main sections are inorganic and organic chemistry. Let's consider what main classes of substances are classified as inorganic and what properties they have.

Main categories of inorganic compounds

These include the following:

1. Oxides.
2. Salt.
3. Grounds.
4. Acids.

Each of the classes is represented by a wide variety of compounds of inorganic nature and is important in almost any structure of human economic and industrial activity. All the main properties characteristic of these compounds, their occurrence in nature and their production are studied in a school chemistry course without fail, in grades 8-11.

There is a general table of oxides, salts, bases, acids, which presents examples of each substance and their state of aggregation and occurrence in nature. It also shows interactions that describe Chemical properties. However, we will look at each of the classes separately and in more detail.

Group of compounds - oxides

4. Reactions as a result of which elements change CO

Me +n O + C = Me 0 + CO

1. Reagent water: formation of acids (SiO 2 exception)

CO + water = acid

2. Reactions with bases:

CO 2 + 2CsOH = Cs 2 CO 3 + H 2 O

3. Reactions with basic oxides: salt formation

P 2 O 5 + 3MnO = Mn 3 (PO 3) 2

4. OVR reactions:

CO 2 + 2Ca = C + 2CaO,

They exhibit dual properties and interact according to the principle of the acid-base method (with acids, alkalis, basic oxides, acid oxides). They do not interact with water.

1. With acids: formation of salts and water

AO + acid = salt + H 2 O

2. With bases (alkalis): formation of hydroxo complexes

Al 2 O 3 + LiOH + water = Li

3. Reactions with acid oxides: obtaining salts

FeO + SO 2 = FeSO 3

4. Reactions with OO: formation of salts, fusion

MnO + Rb 2 O = double salt Rb 2 MnO 2

5. Fusion reactions with alkalis and alkali metal carbonates: formation of salts

Al 2 O 3 + 2LiOH = 2LiAlO 2 + H 2 O

They do not form either acids or alkalis. They exhibit highly specific properties.

Each higher oxide, formed either by a metal or a non-metal, when dissolved in water, gives a strong acid or alkali.

Organic and inorganic acids

In the classical sound (based on the positions of ED - electrolytic dissociation - acids are compounds, in aquatic environment dissociating into cations H + and anions of acid residues An -. However, today acids have also been extensively studied in anhydrous conditions, so there are many different theories for hydroxides.

Empirical formulas of oxides, bases, acids, salts consist only of symbols, elements and indices indicating their quantity in the substance. For example, inorganic acids are expressed by the formula H + acid residue n- . Organic matter have a different theoretical mapping. In addition to the empirical one, you can write down a full and abbreviated structural formula for them, which will reflect not only the composition and quantity of the molecule, but also the order of the atoms, their connection with each other and the main functional group for carboxylic acids -COOH.

In inorganics, all acids are divided into two groups:

• oxygen-free - HBr, HCN, HCL and others;
• oxygen-containing (oxoacids) - HClO 3 and everything where there is oxygen.

Inorganic acids are also classified by stability (stable or stable - everything except carbonic and sulfurous, unstable or unstable - carbonic and sulfurous). In terms of strength, acids can be strong: sulfuric, hydrochloric, nitric, perchloric and others, as well as weak: hydrogen sulfide, hypochlorous and others.

Organic chemistry offers not the same variety. Acids that are organic in nature are classified as carboxylic acids. Their common feature is the presence of the -COOH functional group. For example, HCOOH (formic), CH 3 COOH (acetic), C 17 H 35 COOH (stearic) and others.

There are a number of acids that are especially carefully emphasized when considering this topic in a school chemistry course.

1. Solyanaya.
2. Nitrogen.
3. Orthophosphoric.
4. Hydrobromic.
5. Coal.
6. Hydrogen iodide.
7. Sulfuric.
8. Acetic or ethane.
9. Butane or oil.
10. Benzoin.

These 10 acids in chemistry are fundamental substances of the corresponding class both in the school course and in general in industry and syntheses.

Properties of inorganic acids

The main physical properties include, first of all, the different state of aggregation. After all, there are a number of acids that have the form of crystals or powders (boric, orthophosphoric) under normal conditions. The vast majority of known inorganic acids are different liquids. Boiling and melting points also vary.

Acids can cause severe burns, as they have the power to destroy organic tissue and skin. Indicators are used to detect acids:

• methyl orange (in normal environment - orange, in acids - red),
• litmus (in neutral - violet, in acids - red) or some others.

The most important chemical properties include the ability to interact with both simple and complex substances.

Chemical properties of inorganic acids

What do they interact with?	Example reaction
1. With simple substances - metals. Mandatory condition: the metal must be in the EHRNM before hydrogen, since metals standing after hydrogen are not able to displace it from the composition of acids. The reaction always produces hydrogen gas and salt.
2. With reasons. The result of the reaction is salt and water. Similar reactions strong acids with alkalis are called neutralization reactions.	Any acid (strong) + soluble base = salt and water
3. With amphoteric hydroxides. Bottom line: salt and water.	2HNO 2 + beryllium hydroxide = Be(NO 2) 2 (medium salt) + 2H 2 O
4. With basic oxides. Result: water, salt.	2HCL + FeO = iron (II) chloride + H 2 O
5. With amphoteric oxides. Final effect: salt and water.	2HI + ZnO = ZnI 2 + H 2 O
6. With salts formed by weaker acids. Final effect: salt and weak acid.	2HBr + MgCO 3 = magnesium bromide + H 2 O + CO 2

When interacting with metals, not all acids react equally. Chemistry (9th grade) at school involves a very shallow study of such reactions, however, even at this level the specific properties of concentrated nitric and sulfuric acid when interacting with metals are considered.

Hydroxides: alkalis, amphoteric and insoluble bases

Oxides, salts, bases, acids - all these classes of substances have a common chemical nature, explained by the structure of the crystal lattice, as well as the mutual influence of atoms in the molecules. However, if it was possible to give a very specific definition for oxides, then this is more difficult to do for acids and bases.

Just like acids, bases, according to the ED theory, are substances that can decompose in an aqueous solution into metal cations Me n + and anions of hydroxyl groups OH - .

• Soluble or alkalis (strong bases that change Formed by metals of groups I and II. Example: KOH, NaOH, LiOH (that is, elements of only the main subgroups are taken into account);
• Slightly soluble or insoluble (medium strength, do not change the color of the indicators). Example: magnesium hydroxide, iron (II), (III) and others.
• Molecular (weak bases, in an aqueous environment they reversibly dissociate into ion molecules). Example: N 2 H 4, amines, ammonia.
• Amphoteric hydroxides (show dual basic-acid properties). Example: beryllium, zinc and so on.

Each group presented is studied in the school chemistry course in the “Fundamentals” section. Chemistry in grades 8-9 involves a detailed study of alkalis and poorly soluble compounds.

Main characteristic properties of bases

All alkalis and slightly soluble compounds are found in nature in a solid crystalline state. At the same time, their melting temperatures are usually low, and poorly soluble hydroxides decompose when heated. The color of the bases is different. If alkalis are white, then crystals of poorly soluble and molecular bases can be of very different colors. The solubility of most compounds of this class can be found in the table, which presents the formulas of oxides, bases, acids, salts, and shows their solubility.

Alkalies can change the color of indicators as follows: phenolphthalein - crimson, methyl orange - yellow. This is ensured by the free presence of hydroxo groups in the solution. That is why poorly soluble bases do not give such a reaction.

The chemical properties of each group of bases are different.

Chemical properties
Alkalis	Slightly soluble bases	Amphoteric hydroxides
I. Interact with CO (result - salt and water): 2LiOH + SO 3 = Li 2 SO 4 + water II. Interact with acids (salt and water): ordinary neutralization reactions (see acids) III. They interact with AO to form a hydroxo complex of salt and water: 2NaOH + Me +n O = Na 2 Me +n O 2 + H 2 O, or Na 2 IV. They interact with amphoteric hydroxides to form hydroxo complex salts: The same as with AO, only without water V. React with soluble salts to form insoluble hydroxides and salts: 3CsOH + iron (III) chloride = Fe(OH) 3 + 3CsCl VI. React with zinc and aluminum in an aqueous solution to form salts and hydrogen: 2RbOH + 2Al + water = complex with hydroxide ion 2Rb + 3H 2	I. When heated, they can decompose: insoluble hydroxide = oxide + water II. Reactions with acids (result: salt and water): Fe(OH) 2 + 2HBr = FeBr 2 + water III. Interact with KO: Me +n (OH) n + KO = salt + H 2 O	I. React with acids to form salt and water: (II) + 2HBr = CuBr 2 + water II. React with alkalis: result - salt and water (condition: fusion) Zn(OH) 2 + 2CsOH = salt + 2H 2 O III. React with strong hydroxides: the result is salts if the reaction occurs in an aqueous solution: Cr(OH) 3 + 3RbOH = Rb 3

These are most of the chemical properties that bases exhibit. The chemistry of bases is quite simple and follows the general laws of all inorganic compounds.

Class of inorganic salts. Classification, physical properties

Based on the provisions of the ED, salts can be called inorganic compounds that dissociate in an aqueous solution into metal cations Me +n and anions of acidic residues An n-. This is how you can imagine salts. Chemistry gives more than one definition, but this is the most accurate.

Moreover, according to their chemical nature, all salts are divided into:

• Acidic (containing a hydrogen cation). Example: NaHSO 4.
• Basic (containing a hydroxo group). Example: MgOHNO 3, FeOHCL 2.
• Medium (consist only of a metal cation and an acid residue). Example: NaCL, CaSO 4.
• Double (include two different metal cations). Example: NaAl(SO 4) 3.
• Complex (hydroxo complexes, aqua complexes and others). Example: K 2.

The formulas of salts reflect their chemical nature, and also indicate the qualitative and quantitative composition of the molecule.

Oxides, salts, bases, acids have different solubility properties, which can be viewed in the corresponding table.

If we talk about the state of aggregation of salts, then we need to notice their uniformity. They exist only in solid, crystalline or powdery states. The color range is quite varied. Solutions of complex salts, as a rule, have bright, saturated colors.

Chemical interactions for the class of medium salts

They have similar chemical properties as bases, acids, and salts. Oxides, as we have already examined, are somewhat different from them in this factor.

In total, 4 main types of interactions can be distinguished for medium salts.

I. Interaction with acids (only strong from the point of view of ED) with the formation of another salt and a weak acid:

KCNS + HCL = KCL + HCNS

II. Reactions with soluble hydroxides producing salts and insoluble bases:

CuSO 4 + 2LiOH = 2LiSO 4 soluble salt + Cu(OH) 2 insoluble base

III. Reaction with another soluble salt to form an insoluble salt and a soluble one:

PbCL 2 + Na 2 S = PbS + 2NaCL

IV. Reactions with metals located in the EHRNM to the left of the one that forms the salt. In this case, the reacting metal should not interact with water under normal conditions:

Mg + 2AgCL = MgCL 2 + 2Ag

These are the main types of interactions that are characteristic of medium salts. The formulas of complex, basic, double and acidic salts speak for themselves about the specificity of the chemical properties exhibited.

The formulas of oxides, bases, acids, salts reflect the chemical essence of all representatives of these classes of inorganic compounds, and in addition, give an idea of ​​the name of the substance and its physical properties. Therefore, special attention should be paid to their writing. A huge variety of compounds is offered to us by the generally amazing science of chemistry. Oxides, bases, acids, salts - this is only part of the immense diversity.

Oxides are called complex substances whose molecules include oxygen atoms in oxidation state - 2 and some other element.

can be obtained through the direct interaction of oxygen with another element, or indirectly (for example, during the decomposition of salts, bases, acids). Under normal conditions, oxides come in solid, liquid and gaseous states; this type of compound is very common in nature. Oxides are contained in Earth's crust. Rust, sand, water, carbon dioxide- these are oxides.

They are either salt-forming or non-salt-forming.

Salt-forming oxides- These are oxides that form salts as a result of chemical reactions. These are oxides of metals and non-metals, which, when interacting with water, form the corresponding acids, and when interacting with bases, the corresponding acidic and normal salts. For example, Copper oxide (CuO) is a salt-forming oxide, because, for example, when it reacts with hydrochloric acid (HCl), a salt is formed:

CuO + 2HCl → CuCl 2 + H 2 O.

As a result of chemical reactions, other salts can be obtained:

CuO + SO 3 → CuSO 4.

Non-salt-forming oxides These are oxides that do not form salts. Examples include CO, N 2 O, NO.

Salt-forming oxides, in turn, are of 3 types: basic (from the word « base » ), acidic and amphoteric.

Basic oxides These metal oxides are called those that correspond to hydroxides belonging to the class of bases. Basic oxides include, for example, Na 2 O, K 2 O, MgO, CaO, etc.

Chemical properties of basic oxides

1. Water-soluble basic oxides react with water to form bases:

Na 2 O + H 2 O → 2NaOH.

2. React with acid oxides, forming the corresponding salts

Na 2 O + SO 3 → Na 2 SO 4.

3. React with acids to form salt and water:

CuO + H 2 SO 4 → CuSO 4 + H 2 O.

4. React with amphoteric oxides:

Li 2 O + Al 2 O 3 → 2LiAlO 2.

If the composition of the oxides contains a non-metal or a metal exhibiting the highest valence (usually from IV to VII) as the second element, then such oxides will be acidic. Acidic oxides (acid anhydrides) are those oxides that correspond to hydroxides belonging to the class of acids. These are, for example, CO 2, SO 3, P 2 O 5, N 2 O 3, Cl 2 O 5, Mn 2 O 7, etc. Acidic oxides dissolve in water and alkalis, forming salt and water.

Chemical properties of acid oxides

1. React with water to form an acid:

SO 3 + H 2 O → H 2 SO 4.

But not all acidic oxides react directly with water (SiO 2, etc.).

2. React with based oxides to form a salt:

CO 2 + CaO → CaCO 3

3. React with alkalis, forming salt and water:

CO 2 + Ba(OH) 2 → BaCO 3 + H 2 O.

Part amphoteric oxide includes an element that has amphoteric properties. Amphotericity refers to the ability of compounds to exhibit acidic and basic properties depending on conditions. For example, zinc oxide ZnO can be either a base or an acid (Zn(OH) 2 and H 2 ZnO 2). Amphotericity is expressed in the fact that, depending on the conditions, amphoteric oxides exhibit either basic or acidic properties.

Chemical properties of amphoteric oxides

1. React with acids to form salt and water:

ZnO + 2HCl → ZnCl 2 + H 2 O.

2. React with solid alkalis (during fusion), forming as a result of the reaction salt - sodium zincate and water:

ZnO + 2NaOH → Na 2 ZnO 2 + H 2 O.

When zinc oxide interacts with an alkali solution (the same NaOH), another reaction occurs:

ZnO + 2 NaOH + H 2 O => Na 2.

Coordination number is a characteristic that determines the number of nearby particles: atoms or ions in a molecule or crystal. Each amphoteric metal has its own coordination number. For Be and Zn it is 4; For and Al it is 4 or 6; For and Cr it is 6 or (very rarely) 4;

Amphoteric oxides are usually insoluble in water and do not react with it.

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