Dear readers!

Formation and destruction
complex salts as an example
hydroxo complexes

In our city, the Unified State Exam in Chemistry has been taken since 2003. Over the past five years, we have accumulated some work experience. Two of my students had the highest scores in the region - 97 (2004) and 96 (2007). Level C tasks go far beyond the scope of the two-hour school curriculum, for example, drawing up equations for redox reactions or reaction equations for the destruction of complex salts. Sometimes it is not possible to find answers to some questions in any textbook or manual.

One of the tasks of a high level of complexity (level C) tests knowledge about the amphoteric properties of substances. To successfully complete this task, you need to know, among other things, how to destroy complex salts. Insufficient attention is paid to this issue in the educational literature.

Oxides and hydroxides of many metals have amphoteric properties. They are insoluble in water, but react with both acids and alkalis. When preparing for the Unified State Exam, you need to learn material about the properties of compounds zinc, beryllium, aluminum, iron And chromium. Let us consider these properties from the point of view of amphotericity.

1 Basic properties when interacting with strong acids.

For example:

ZnO + 2HCl = ZnCl 2 + H 2 O,

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

Al 2 O 3 + 6HCl = 2AlCl 3 + 3H 2 O,

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

2 Acidic properties when interacting with alkalis.

1) Reactions during fusion:

The formula of zinc hydroxide is written in acid form - H 2 ZnO 2 (zinc acid).

The acid form of aluminum hydroxide is H 3 AlO 3 (orthoaluminum acid), but it is unstable, and water is split off when heated:

H 3 AlO 3 H 2 O + HAlO 2,

meta-aluminum acid is obtained. For this reason, when aluminum compounds are fused with alkalis, salts are obtained - metaaluminates:

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

Al 2 O 3 + 2NaOH 2NaAlO 2 + H 2 O.

2) Reactions in solution occur with the formation complex salts:

It should be noted that when aluminum compounds interact with alkalis in solution, different forms of complex salts are obtained:

Na 3 – sodium hexahydroxoaluminate;

Na – sodium tetrahydroxodiaquaaluminate.

The form of salt depends on the concentration of alkali.

Beryllium compounds (BeO and Be(OH) 2) react with alkalis similarly to zinc compounds, chromium(III) and iron(III) compounds (Cr 2 O 3, Cr(OH) 3, Fe 2 O 3, Fe(OH) 3 ) - similar to aluminum compounds, but the oxides of these metals interact with alkalis only during fusion.

When hydroxides of these metals react with alkalis in solution, complex salts with a coordination number of 6 are obtained.

Chromium(III) hydroxide is easily soluble in alkalis:

Iron(III) hydroxide has very weak amphoteric properties and interacts only with hot concentrated solutions of alkalis:

3 Metal beryllium, zinc and aluminum interact with alkali solutions, displacing hydrogen from them:

Iron and chromium do not react with alkali solutions; the formation of salts is possible only when fused with solid alkalis.

4 By revising methods of destruction hydroxo complexes Several cases can be distinguished.

1) When exposed to an excess of strong acid, two medium salts and water are obtained:

Na + 4HCl (g) = NaCl + AlCl 3 + 4H 2 O,

K 3 + 6HNO 3 (ex.) = 3KNO 3 + Cr(NO 3) 3 + 6H 2 O.

2) Under the action of a strong acid (in deficiency), the average salt of the active metal, amphoteric hydroxide and water are obtained:

Na + HCl = NaCl + Al(OH) 3 + H 2 O,

K 3 + 3HNO 3 = 3KNO 3 + Cr(OH) 3 + 3H 2 O.

3) When exposed to a weak acid, an acid salt of the active metal, amphoteric hydroxide and water are obtained:

Na + H 2 S = NaHS + Al(OH) 3 + H 2 O,

K 3 + 3H 2 CO 3 = 3KHCO 3 + Cr(OH) 3 + 3H 2 O.

4) When exposed to carbon dioxide or sulfur dioxide, an acid salt of the active metal and an amphoteric hydroxide are obtained:

Na + CO 2 = NaHCO 3 + Al(OH) 3,

K 3 + 3SO 2 = 3KHSO 3 + Cr(OH) 3.

5) Under the action of salts formed by strong acids and cations Fe 3+, Al 3+ and Cr 3+, mutual enhancement of hydrolysis occurs, two amphoteric hydroxides and a salt of the active metal are obtained:

3Na + FeCl 3 = 3Al(OH) 3 + Fe(OH) 3 + 3NaCl,

K 3 + Al(NO 3) 3 = Al(OH) 3 + Cr(OH) 3 + 3KNO 3.

Write equations for the four possible reactions between them.

3) Write the equations of four possible reactions between solutions of potassium hexahydroxoaluminate, potassium carbonate, carbonic acid, chromium(III) chloride.

4) Carry out transformations:

Chemical equations

Chemical equation is the expression of a reaction using chemical formulas. Chemical equations show which substances enter into a chemical reaction and which substances are formed as a result of this reaction. The equation is compiled on the basis of the law of conservation of mass and shows the quantitative relationships of substances participating in a chemical reaction.

As an example, consider the interaction of potassium hydroxide with phosphoric acid:

H 3 PO 4 + 3 KOH = K 3 PO 4 + 3 H 2 O.

From the equation it is clear that 1 mole of orthophosphoric acid (98 g) reacts with 3 moles of potassium hydroxide (3·56 g). As a result of the reaction, 1 mole of potassium phosphate (212 g) and 3 moles of water (3·18 g) are formed.

98 + 168 = 266 g; 212 + 54 = 266 g we see that the mass of substances that entered into the reaction is equal to the mass of the reaction products. The equation of a chemical reaction allows you to make various calculations related to a given reaction.

Complex substances are divided into four classes: oxides, bases, acids and salts.

Oxides- these are complex substances consisting of two elements, one of which is oxygen, i.e. An oxide is a compound of an element with oxygen.

The name of oxides is derived from the name of the element that is part of the oxide. For example, BaO is barium oxide. If the oxide element has a variable valency, then after the name of the element its valence is indicated in parentheses with a Roman numeral. For example, FeO is iron (I) oxide, Fe2O3 is iron (III) oxide.

All oxides are divided into salt-forming and non-salt-forming.

Salt-forming oxides 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 → CuCl2 + H2O.

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

CuO + SO3 → CuSO4.

Non-salt-forming oxides are those oxides that do not form salts. Examples include CO, N2O, NO.

Salt-forming oxides are of 3 types: basic (from the word “base”), acidic and amphoteric.

Basic oxides are metal oxides, which correspond to hydroxides, which belong to the class of bases. Basic oxides include, for example, Na2O, K2O, MgO, CaO, etc.

Chemical properties of basic oxides

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

Na2O + H2O → 2NaOH.

2. React with acid oxides, forming the corresponding salts

Na2O + SO3 → Na2SO4.

3. React with acids to form salt and water:

CuO + H2SO4 → CuSO4 + H2O.

4. React with amphoteric oxides:

Li2O + Al2O3 → 2LiAlO2.

5. Basic oxides react with acidic oxides to form salts:

Na2O + SO3 = Na2SO4

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, CO2, SO3, P2O5, N2O3, Cl2O5, Mn2O7, 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:

SO3 + H2O → H2SO4.

But not all acidic oxides react directly with water (SiO2, etc.).

2. React with based oxides to form a salt:

CO2 + CaO → CaCO3

3. React with alkalis, forming salt and water:

CO2 + Ba(OH)2 → BaCO3 + H2O.

An amphoteric oxide contains 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 H2ZnO2). Amphotericity is expressed in the fact that, depending on the conditions, amphoteric oxides exhibit either basic or acidic properties, for example, Al2O3, Cr2O3, MnO2; Fe2O3 ZnO. For example, the amphoteric nature of zinc oxide manifests itself when it interacts with both hydrochloric acid and sodium hydroxide:

ZnO + 2HCl = ZnCl 2 + H 2 O

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

Since not all amphoteric oxides are soluble in water, it is much more difficult to prove the amphoteric nature of such oxides. For example, aluminum (III) oxide exhibits basic properties in the reaction of its fusion with potassium disulfate, and acidic properties when fused with hydroxides:

Al2O3 + 3K2S2O7 = 3K2SO4 + A12(SO4)3

Al2O3 + 2KOH = 2KAlO2 + H2O

For different amphoteric oxides, the duality of properties can be expressed to varying degrees. For example, zinc oxide dissolves equally easily in both acids and alkalis, and iron (III) oxide - Fe2O3 - has predominantly basic properties.

Chemical properties of amphoteric oxides

1. React with acids to form salt and water:

ZnO + 2HCl → ZnCl2 + H2O.

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

ZnO + 2NaOH → Na2 ZnO2 + H2O.

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

ZnO + 2 NaOH + H2O => Na2.

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.

Methods for producing oxides from simple substances are either a direct reaction of the element with oxygen:

or decomposition of complex substances:

a) oxides

4CrO3 = 2Cr2O3 + 3O2-

b) hydroxides

Ca(OH)2 = CaO + H2O

c) acids

H2CO3 = H2O + CO2-

CaCO3 = CaO +CO2

As well as the interaction of acids - oxidizing agents with metals and non-metals:

Cu + 4HNO3 (conc) = Cu(NO3) 2 + 2NO2 + 2H2O

Oxides can be obtained by 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 found in the Earth's crust. Rust, sand, water, carbon dioxide are oxides.

Reasons- these are complex substances in the molecules of which metal atoms are connected to one or more hydroxyl groups.

Bases are electrolytes that, when dissociated, form only hydroxide ions as anions.

NaOH = Na + + OH -

Ca(OH)2 = CaOH + + OH - = Ca 2 + + 2OH -

There are several signs of classification of bases:

Depending on their solubility in water, bases are divided into alkalis and insoluble. Alkalis are hydroxides of alkali metals (Li, Na, K, Rb, Cs) and alkaline earth metals (Ca, Sr, Ba). All other bases are insoluble.

Depending on the degree of dissociation, bases are divided into strong electrolytes (all alkalis) and weak electrolytes (insoluble bases).

Depending on the number of hydroxyl groups in the molecule, bases are divided into monoacid (1 OH group), for example, sodium hydroxide, potassium hydroxide, diacid (2 OH groups), for example, calcium hydroxide, copper hydroxide (2), and polyacid.

Chemical properties.

OH - ions in solution determine the alkaline environment.

Alkali solutions change the color of indicators:

Phenolphthalein: colorless ® crimson,

Litmus: violet ® blue,

Methyl orange: orange ® yellow.

Alkali solutions react with acidic oxides to form salts of those acids that correspond to the reacting acidic oxides. Depending on the amount of alkali, medium or acidic salts are formed. For example, when calcium hydroxide reacts with carbon(IV) monoxide, calcium carbonate and water are formed:

Ca(OH)2 + CO2 = CaCO3? + H2O

And when calcium hydroxide reacts with excess carbon monoxide (IV), calcium bicarbonate is formed:

Ca(OH)2 + CO2 = Ca(HCO3)2

Ca2+ + 2OH- + CO2 = Ca2+ + 2HCO32-

All bases react with acids to form salt and water, for example: when sodium hydroxide reacts with hydrochloric acid, sodium chloride and water are formed:

NaOH + HCl = NaCl + H2O

Na+ + OH- + H+ + Cl- = Na+ + Cl- + H2O

Copper(II) hydroxide dissolves in hydrochloric acid to form copper(II) chloride and water:

Cu(OH)2 + 2HCl = CuCl2 + 2H2O

Cu(OH)2 + 2H+ + 2Cl- = Cu2+ + 2Cl- + 2H2O

Cu(OH)2 + 2H+ = Cu2+ + 2H2O.

The reaction between an acid and a base is called a neutralization reaction.

Insoluble bases, when heated, decompose into water and the metal oxide corresponding to the base, for example:

Cu(OH)2 = CuO + H2 2Fe(OH)3 = Fe2O3 + 3H2O

Alkalies interact with salt solutions if one of the conditions for the ion exchange reaction to proceed to completion is met (a precipitate forms),

2NaOH + CuSO4 = Cu(OH)2? + Na2SO4

2OH- + Cu2+ = Cu(OH)2

The reaction occurs due to the binding of copper cations with hydroxide ions.

When barium hydroxide reacts with a solution of sodium sulfate, a precipitate of barium sulfate is formed.

Ba(OH)2 + Na2SO4 = BaSO4? + 2NaOH

Ba2+ + SO42- = BaSO4

The reaction occurs due to the binding of barium cations and sulfate anions.

Acids - These are complex substances whose molecules include hydrogen atoms that can be replaced or exchanged for metal atoms and an acid residue.

Based on the presence or absence of oxygen in the molecule, acids are divided into oxygen-containing (H2SO4 sulfuric acid, H2SO3 sulfurous acid, HNO3 nitric acid, H3PO4 phosphoric acid, H2CO3 carbonic acid, H2SiO3 silicic acid) and oxygen-free (HF hydrofluoric acid, HCl hydrochloric acid (hydrochloric acid) , HBr hydrobromic acid, HI hydroiodic acid, H2S hydrosulfide acid).

Depending on the number of hydrogen atoms in the acid molecule, acids are monobasic (with 1 H atom), dibasic (with 2 H atoms) and tribasic (with 3 H atoms).

ACIDS

The part of an acid molecule without hydrogen is called an acid residue.

Acid residues can consist of one atom (-Cl, -Br, -I) - these are simple acid residues, or they can consist of a group of atoms (-SO3, -PO4, -SiO3) - these are complex residues.

In aqueous solutions, during exchange and substitution reactions, acidic residues are not destroyed:

H2SO4 + CuCl2 → CuSO4 + 2 HCl

The word anhydride means anhydrous, that is, an acid without water. For example,

H2SO4 - H2O → SO3. Anoxic acids do not have anhydrides.

The acid gets its name from the name of the acid-forming element (acid-forming agent) with the addition of the endings “naya” and less often “vaya”: H2SO4 - sulfuric; H2SO3 - coal; H2SiO3 - silicon, etc.

The element can form several oxygen acids. In this case, the indicated endings in the names of acids will be when the element exhibits a higher valence (the acid molecule contains a high content of oxygen atoms). If the element exhibits a lower valence, the ending in the name of the acid will be “empty”: HNO3 - nitric, HNO2 - nitrous.

Acids can be obtained by dissolving anhydrides in water. If the anhydrides are insoluble in water, the acid can be obtained by the action of another stronger acid on the salt of the required acid. This method is typical for both oxygen and oxygen-free acids. Oxygen-free acids are also obtained by direct synthesis from hydrogen and a non-metal, followed by dissolving the resulting compound in water:

H2 + Cl2 → 2 HCl;

Solutions of the resulting gaseous substances HCl and H2S are acids.

Under normal conditions, acids exist in both liquid and solid states.

Chemical properties of acids

1. Acid solutions act on indicators. All acids (except silicic) are highly soluble in water. Special substances - indicators allow you to determine the presence of acid.

Indicators are substances of complex structure. They change color depending on their interaction with different chemicals. In neutral solutions they have one color, in solutions of bases they have another color. When interacting with an acid, they change their color: the methyl orange indicator turns red, and the litmus indicator also turns red.

2. React with bases to form water and a salt, which contains an unchanged acidic residue (neutralization reaction):

H2SO4 + Ca(OH)2 → CaSO4 + 2 H2O.

3. React with base oxides to form water and salt. The salt contains the acidic residue of the acid that was used in the neutralization reaction:

H3PO4 + Fe2O3 → 2 FePO4 + 3 H2O.

4. Interact with metals.

For acids to interact with metals, certain conditions must be met:

1. The metal must be sufficiently active with respect to acids (in the series of activity of metals it must be located before hydrogen). The further to the left a metal is in the activity series, the more intensely it interacts with acids;

K, Ca, Na, Mn, Al, Zn, Fe, Ni, Sn, Pb, H2, Cu, Hg, Ag, Au.

But the reaction between a solution of hydrochloric acid and copper is impossible, since copper is in the voltage series after hydrogen.

2. The acid must be strong enough (that is, capable of donating hydrogen ions H+).

When chemical reactions of acid with metals occur, salt is formed and hydrogen is released (except for the interaction of metals with nitric and concentrated sulfuric acids):

Zn + 2HCl → ZnCl2 + H2;

Cu + 4HNO3 → CuNO3 + 2 NO2 + 2 H2O.

However, no matter how different the acids are, they all form hydrogen cations upon dissociation, which determine a number of common properties: sour taste, change in the color of indicators (litmus and methyl orange), interaction with other substances.

The same reaction occurs between metal oxides and most acids

CuO+ H2SO4 = CuSO4+ H2O

Let's describe the reactions:

2) The second reaction should produce a soluble salt. In many cases, the interaction of the metal with the acid practically does not occur because the resulting salt is insoluble and covers the surface of the metal with a protective film, for example:

Рb + H2SO4 =/ PbSO4 + H2

Insoluble lead(II) sulfate stops the acid from reaching the metal, and the reaction stops just before it begins. For this reason, most heavy metals practically do not interact with phosphoric, carbonic and hydrosulfide acids.

3) The third reaction is characteristic of acid solutions, therefore, insoluble acids, such as silicic acid, do not react with metals. A concentrated solution of sulfuric acid and a solution of nitric acid of any concentration interact with metals somewhat differently, therefore the reaction equations between metals and these acids are written in a different way. A dilute solution of sulfuric acid reacts with metals. standing in the voltage series to hydrogen, forming salt and hydrogen.

4) The fourth reaction is a typical ion exchange reaction and occurs only if a precipitate or gas is formed.

Salts - these are complex substances whose molecules consist of metal atoms and acidic residues (sometimes they may contain hydrogen). For example, NaCl is sodium chloride, CaSO4 is calcium sulfate, etc.

Almost all salts are ionic compounds, therefore, ions of acidic residues and metal ions are bound together in salts:

Na+Cl - sodium chloride

Ca2+SO42 - calcium sulfate, etc.

A salt is the product of partial or complete substitution of a metal for the hydrogen atoms of an acid.

Hence, the following types of salts are distinguished:

1. Medium salts - all hydrogen atoms in the acid are replaced by a metal: Na2CO3, KNO3, etc.

2. Acidic salts - not all hydrogen atoms in the acid are replaced by a metal. Of course, acid salts can only form di- or polybasic acids. Monobasic acids cannot produce acid salts: NaHCO3, NaH2PO4, etc. d.

3. Double salts - the hydrogen atoms of a di- or polybasic acid are replaced not by one metal, but by two different ones: NaKCO3, KAl(SO4)2, etc.

4. Basic salts can be considered as products of incomplete, or partial, substitution of hydroxyl groups of bases with acidic residues: Al(OH)SO4, Zn(OH)Cl, etc.

According to international nomenclature, the name of the salt of each acid comes from the Latin name of the element. For example, salts of sulfuric acid are called sulfates: CaSO4 - calcium sulfate, MgSO4 - magnesium sulfate, etc.; salts of hydrochloric acid are called chlorides: NaCl - sodium chloride, ZnCI2 - zinc chloride, etc.

The particle “bi” or “hydro” is added to the name of salts of dibasic acids: Mg(HCl3)2 - magnesium bicarbonate or bicarbonate.

Provided that in a tribasic acid only one hydrogen atom is replaced by a metal, then the prefix “dihydro” is added: NaH2PO4 - sodium dihydrogen phosphate.

Salts are solid substances with very different solubility in water.

The chemical properties of salts are determined by the properties of the cations and anions that are part of them.

1. Some salts decompose when heated:

CaCO3 = CaO + CO2

2. React with acids to form a new salt and a new acid. To carry out this reaction, the acid must be stronger than the salt affected by the acid:

2NaCl + H2SO4 → Na2SO4 + 2HCl.

3. Interact with bases, forming a new salt and a new base:

Ba(OH)2 + MgSO4 → BaSO4↓ + Mg(OH)2.

4. Interact with each other to form new salts:

NaCl + AgNO3 → AgCl + NaNO3.

5. They interact with metals that are in the same range of activity as the metal that is part of the salt.

This lesson is devoted to the study of the general chemical properties of another class of inorganic substances - salts. You will learn what substances salts can interact with and what are the conditions for such reactions to occur.

Topic: Classes of inorganic substances

Lesson: Chemical properties of salts

1. Interaction of salts with metals

Salts are complex substances consisting of metal atoms and acidic residues.

Therefore, the properties of salts will be associated with the presence of a particular metal or acidic residue in the composition of the substance. For example, most copper salts in solution are bluish in color. Salts of manganese acid (permanganates) are mainly purple. Let's start getting acquainted with the chemical properties of salts with the following experiment.

Place an iron nail in the first glass with a solution of copper (II) sulfate. Place a copper plate in the second glass with a solution of iron (II) sulfate. We also lower the copper plate into the third glass with the silver nitrate solution. After some time, we will see that the iron nail was covered with a layer of copper, the copper plate from the third glass was covered with a layer of silver, and nothing happened to the copper plate from the second glass.

Rice. 1. Interaction of salt solutions with metals

Let us explain the results of the experiment. Reactions only occurred if the metal reacting with the salt was more reactive than the metal in the salt. The activity of metals can be compared with each other by their position in the activity series. The further to the left a metal is located in this row, the greater its ability to displace another metal from the salt solution.

Equations of the reactions carried out:

Fe + CuSO4 = FeSO4 + Cu

When iron reacts with a solution of copper (II) sulfate, pure copper and iron (II) sulfate are formed. This reaction is possible because iron has greater reactivity than copper.

Cu + FeSO4 → reaction does not occur

The reaction between copper and a solution of iron (II) sulfate does not occur, since copper cannot replace iron from the salt solution.

Cu+2AgNO3=2Ag+Cu(NO3)2

When copper reacts with a solution of silver nitrate, silver and copper (II) nitrate are formed. Copper replaces silver from a solution of its salt, since copper is located in the activity series to the left of silver.

Salt solutions can interact with metals that are more active than the metal in the salt. These reactions are of the substitution type.

2. Interaction of salt solutions with each other

Let's consider another property of salts. Salts dissolved in water can interact with each other. Let's conduct an experiment.

Mix solutions of barium chloride and sodium sulfate. As a result, a white precipitate of barium sulfate will form. Obviously there was a reaction.

Reaction equation: BaCl2 + Na2SO4 = BaSO4 + 2NaCl

Salts dissolved in water can undergo an exchange reaction if the result is a water-insoluble salt.

3. Interaction of salts with alkalis

Let's find out whether salts interact with alkalis by conducting the following experiment.

Add a solution of sodium hydroxide to a solution of copper (II) sulfate. The result is a blue precipitate.

Rice. 2. Interaction of copper(II) sulfate solution with alkali

Equation of the reaction: CuSO4 + 2NaOH = Cu(OH)2 + Na2SO4

This reaction is an exchange reaction.

Salts can react with alkalis if the reaction produces a substance that is insoluble in water.

4. Interaction of salts with acids

Add a solution of hydrochloric acid to the sodium carbonate solution. As a result, we see the release of gas bubbles. Let us explain the results of the experiment by writing the equation for this reaction:

Na2CO3 + 2HCl= 2NaCl + H2CO3

H2CO3 = H2O + CO2

Carbonic acid is an unstable substance. It decomposes into carbon dioxide and water. This reaction is an exchange reaction.

Salts can undergo an exchange reaction with acids if the reaction produces gas or forms a precipitate.

1. Collection of problems and exercises in chemistry: 8th grade: for textbooks. P. A. Orzhekovsky and others “Chemistry. 8th grade” / P. A. Orzhekovsky, N. A. Titov, F. F. Hegele. – M.: AST: Astrel, 2006. (p.107-111)

2. Ushakova O. V. Workbook on chemistry: 8th grade: to the textbook by P. A. Orzhekovsky and others “Chemistry. 8th grade” / O. V. Ushakova, P. I. Bespalov, P. A. Orzhekovsky; under. ed. prof. P. A. Orzhekovsky - M.: AST: Astrel: Profizdat, 2006. (p. 108-110)

3. Chemistry. 8th grade. Textbook for general education institutions / P. A. Orzhekovsky, L. M. Meshcheryakova, M. M. Shalashova. – M.: Astrel, 2013. (§34)

4. Chemistry: 8th grade: textbook. for general education institutions / P. A. Orzhekovsky, L. M. Meshcheryakova, L. S. Pontak. M.: AST: Astrel, 2005. (§40)

5. Chemistry: inorg. chemistry: textbook. for 8th grade. general education institutions / G. E. Rudzitis, F. G. Feldman. – M.: Education, OJSC “Moscow Textbooks”, 2009. (§33)

6. Encyclopedia for children. Volume 17. Chemistry / Chapter. ed. V. A. Volodin, leading scientific ed. I. Leenson. – M.: Avanta+, 2003.

Additional web resources

1. Interactions of acids with salts.

2. Interactions of metals with salts.

Homework

1) p. 109-110 No. 4.5 from the Workbook in Chemistry: 8th grade: to the textbook by P. A. Orzhekovsky and others “Chemistry. 8th grade” / O. V. Ushakova, P. I. Bespalov, P. A. Orzhekovsky; under. ed. prof. P. A. Orzhekovsky - M.: AST: Astrel: Profizdat, 2006.

2) p. 193 No. 2,3 from the textbook by P. A. Orzhekovsky, L. M. Meshcheryakova, M. M. Shalashova “Chemistry: 8th grade,” 2013.

DEFINITION

Salts are electrolytes, the dissociation of which produces metal cations (ammonium ions or complex ions) and anions of acidic residues:

\(\ \mathrm(NaNOZ) \mapsto \mathrm(Na)++\mathrm(NOZ)_(-) \);

\(\ \mathrm(NH) 4 \mathrm(NO) 3 \leftrightarrow \mathrm(NH) 4++\mathrm(NO) 3_(-) \);

\(\ \mathrm(KAl)(\mathrm(SO) 4) 2 \leftrightarrow \mathrm(K)++\mathrm(Al) 3++2 \mathrm(SO) 42- \);

\(\ [\mathrm(Zn)(\mathrm(NH) 3) 4] \mathrm(Cl) 2[\mathrm(Zn)(\mathrm(NH) 3) 4] 2++2 \mathrm(Cl) \).

Salts are usually divided into three groups: medium (\(\ \mathrm(NaCl) \)), acidic (\(\ \mathrm(NaHCO) 3 \)) and basic (\(\ \mathrm(Fe)(\mathrm( OH))\mathrm(Cl)\)). In addition, there are double (mixed) and complex salts. Double salts are formed by two cations and one anion. They exist only in solid form.

Chemical properties of salts

a) acid salts

Acid salts upon dissociation give metal cations (ammonium ion), hydrogen ions and anions of the acid residue:

\(\ \mathrm(NaHCO) 3+\mathrm(Na)++\mathrm(H)++\mathrm(CO) 32 \).

Acid salts are products of incomplete replacement of hydrogen atoms by the corresponding acid with metal atoms.

Acid salts are thermally unstable and, when heated, decompose to form intermediate salts:

\(\ \mathrm(Ca)(\mathrm(HCO) 3) 2=\mathrm(CaCOZ) \downarrow+\mathrm(CO) 2 \uparrow+\mathrm(H) 2 \mathrm(O) \).

Neutralization reactions with alkalis are characteristic of acid salts:

\(\ \mathrm(Ca)(\mathrm(HCO) 3) 2+\mathrm(Ca)(\mathrm(OH)) 2=2 \mathrm(Ca) \mathrm(CO) 3 \downarrow+2 \mathrm (H) 2 \mathrm(O) \).

b) basic salts

During dissociation, basic salts produce metal cations, acid anions and OH ions:

\(\ \mathrm(Fe)(\mathrm(OH)) \mathrm(Cl) \rightarrow \mathrm(Fe)(\mathrm(OH))++\mathrm(Cl)-+\mathrm(Fe) 2+ +\mathrm(OH)-+\mathrm(Cl)\).

Basic salts are products of incomplete replacement of hydroxyl groups of the corresponding base with acidic residues.

Basic salts, as well as acidic salts, are thermally unstable and decompose when heated:

\(\ [\mathrm(Cu)(\mathrm(OH))] 2 \mathrm(CO) 3=2 \mathrm(CuO)+\mathrm(CO) 2+\mathrm(H) 2 \mathrm(O) \).

Neutralization reactions with acids are characteristic of basic salts:

\(\ \mathrm(Fe)(\mathrm(OH)) \mathrm(Cl)+\mathrm(HCl) \& \text ( bull; ) \mathrm(FeCl) 2+\mathrm(H) 2 \mathrm( O)\).

c) medium salt

During dissociation, middle salts yield only metal cations (ammonium ion) and acid moiety anions (see above). Medium salts are the products of complete replacement of the hydrogen atoms of the corresponding acid with metal atoms.

Most medium salts are thermally unstable and decompose when heated:

\(\ \mathrm(CaCO) 3=\mathrm(CaO)+\mathrm(CO) 2 \);

\(\ \mathrm(NH) 4 \mathrm(Cl)=\mathrm(NH) 3+\mathrm(HCl) \);

\(\ 2 \mathrm(Cu)(\mathrm(NO) 3) 2=2 \mathrm(CuO)+4 \mathrm(NO) 2+\mathrm(O) 2 \).

In an aqueous solution, salts undergo hydrolysis:

\(\ \mathrm(Al) 2 \mathrm(S) 3+6 \mathrm(H) 2 \mathrm(O) 2 \mathrm(Al)(\mathrm(OH)) 3+3 \mathrm(H) 2 \mathrm(S)\);

\(\ \mathrm(K) 2 \mathrm(S)+\mathrm(H) 2 \mathrm(O) \rightarrow \mathrm(KHS)+\mathrm(KOH) \);

\(\ \mathrm(Fe)(\mathrm(NO) 3) 3+\mathrm(H) 2 \mathrm(O) \rightarrow \mathrm(Fe)(\mathrm(OH))(\mathrm(NO) 3 ) 2+\mathrm(HNO) 3\).

Medium salts enter into exchange reactions with acids, bases and other salts:

\(\ \mathrm(Pb)(\mathrm(NO) 3) 2+\mathrm(H) 2 \mathrm(S)=\mathrm(PbS) \downarrow+2 \mathrm(HNO) 3 \);

\(\ \mathrm(Fe) 2(\mathrm(SO) 4) 3+3 \mathrm(Ba)(\mathrm(OH)) 2=2 \mathrm(Fe)(\mathrm(OH)) 3 \downarrow +3 \mathrm(BaSO) 4\downarrow \);

\(\ \mathrm(CaBr) 2+\mathrm(K) 2 \mathrm(CO) 3=\mathrm(CaCO) 3 \downarrow+2 \mathrm(KBr) \).

Physical properties of salts

Most often, salts are crystalline substances with an ionic crystal lattice. Salts have high melting points. When n. salts are dielectrics. The solubility of salts in water varies.

Obtaining salts

a) acid salts

The main methods for obtaining acid salts are incomplete neutralization of acids, the effect of excess acid oxides on bases and the effect of acids on salts:

\(\ \mathrm(NaOH)+\mathrm(H) 2 \mathrm(SO) 4=\mathrm(NaHSO) 4+\mathrm(H) 2 \mathrm(O) \);

\(\ \mathrm(Ca)(\mathrm(OH)) 2+2 \mathrm(CO) 2=\mathrm(Ca)(\mathrm(HCO) 3) 2 \);

\(\ \mathrm(CaCO) 3+\mathrm(CO) 2+\mathrm(H) 2 \mathrm(O)=\mathrm(Ca)(\mathrm(HCO) 3) 2\).

b) basic salts

Basic salts are prepared by carefully adding a small amount of alkali to a brine solution or by reacting weak acids with medium salts:

\(\ \mathrm(AICl) 3+2 \mathrm(NaOH)=\mathrm(Al)(\mathrm(OH)) 2 \mathrm(Cl)+2 \mathrm(NaCl) \);

\(\ 2 \mathrm(MgCl) 2+2 \mathrm(Na) 2 \mathrm(CO) 3+\mathrm(H) 2 \mathrm(O)=[\mathrm(Mg)(\mathrm(OH)) ] 2 \mathrm(CO) 3 \downarrow+\mathrm(CO) 2+2 \mathrm(NaCl) \).

c) medium salt

The main methods for obtaining salts of the medium are the reaction of acids with metals, basic or amphoteric oxides and bases, as well as the reaction of bases with acidic or amphoteric oxides and acids, the reaction of acids and basic oxides and the exchange reaction:

\(\ \mathrm(Mg)+\mathrm(H) 2 \mathrm(SO) 4=\mathrm(MgSO) 4+\mathrm(H) 2 \);

\(\ \mathrm(Ag) 2 \mathrm(O)+2 \mathrm(HNO) \mathbf(3)=2 \mathrm(AgNO) \mathbf(3)+\mathrm(H) 2 \mathrm(O) \);

\(\ \mathrm(Cu)(\mathrm(OH)) 2+2 \mathrm(HCl)=\mathrm(CuCl) 2+2 \mathrm(H) 20 \);

\(\ 2 \mathrm(KOH)+\mathrm(SO) 2=\mathrm(K) 2 \mathrm(SO) 3+\mathrm(H) 20 \);

\(\ \mathrm(CaO)+\mathrm(SO) 3=\mathrm(CaSO) 4 \);

\(\ \mathrm(BaCl) 2+\mathrm(MgSO) 4=\mathrm(MgCl) 2+\mathrm(BaSO) 4\downarrow \).

Examples of problem solving

Salts are complex substances whose molecules consist of metal atoms and acidic residues (sometimes they may contain hydrogen). For example, NaCl is sodium chloride, CaSO 4 is calcium sulfate, etc.

Practically all salts are ionic compounds, Therefore, in salts, ions of acidic residues and metal ions are bound together:

Na + Cl – – sodium chloride

Ca 2+ SO 4 2– – calcium sulfate, etc.

A salt is the product of partial or complete substitution of a metal for the hydrogen atoms of an acid. Hence, the following types of salts are distinguished:

1. Medium salts– all hydrogen atoms in the acid are replaced by a metal: Na 2 CO 3, KNO 3, etc.

2. Acid salts– not all hydrogen atoms in the acid are replaced by a metal. Of course, acid salts can only form di- or polybasic acids. Monobasic acids cannot produce acidic salts: NaHCO 3, NaH 2 PO 4, etc. d.

3. Double salts– the hydrogen atoms of a di- or polybasic acid are replaced not by one metal, but by two different ones: NaKCO 3, KAl(SO 4) 2, etc.

4. Basic salts can be considered as products of incomplete, or partial, substitution of hydroxyl groups of bases with acidic residues: Al(OH)SO 4, Zn(OH)Cl, etc.

According to international nomenclature, the name of the salt of each acid comes from the Latin name of the element. For example, salts of sulfuric acid are called sulfates: CaSO 4 - calcium sulfate, Mg SO 4 - magnesium sulfate, etc.; salts of hydrochloric acid are called chlorides: NaCl - sodium chloride, ZnCI 2 - zinc chloride, etc.

The particle “bi” or “hydro” is added to the name of salts of dibasic acids: Mg(HCl 3) 2 – magnesium bicarbonate or bicarbonate.

Provided that in a tribasic acid only one hydrogen atom is replaced by a metal, then the prefix “dihydro” is added: NaH 2 PO 4 - sodium dihydrogen phosphate.

Salts are solid substances with very different solubility in water.

Chemical properties of salts

The chemical properties of salts are determined by the properties of the cations and anions that are part of them.

1. Some salts decompose when heated:

CaCO 3 = CaO + CO 2

2. Interact with acids with the formation of a new salt and a new acid. To carry out this reaction, the acid must be stronger than the salt affected by the acid:

2NaCl + H 2 SO 4 → Na 2 SO 4 + 2HCl.

3. Interact with bases, forming a new salt and a new base:

Ba(OH) 2 + MgSO 4 → BaSO 4 ↓ + Mg(OH) 2.

4. Interact with each other with the formation of new salts:

NaCl + AgNO 3 → AgCl + NaNO 3 .

5. Interact with metals, which are in the range of activity to the metal that is part of the salt:

Fe + CuSO 4 → FeSO 4 + Cu↓.

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