11 acids in chemistry. Acids presentation for a lesson in chemistry (grade 11) on the topic

Sour taste, action on indicators, electrical conductivity, interaction with metals, basic and amphoteric oxides, bases and salts, formation of esters with alcohols - these properties are common to inorganic and organic acids.

1. In water, acids dissociate into hydrogen cations and anions of acid residues, for example:

Acid solutions change the color of indicators: litmus - into red, methyl orange - into pink, the color of phenolphthalein does not change.

2. Solutions of acids react with metals standing in the electrochemical series of voltages to the left of hydrogen, subject to a number of conditions, the most important of which is the formation of a soluble salt as a result of the reaction. Considering this property of inorganic and organic acids, we emphasize that the interaction of HNO 3 and H 2 SO 4 (conc.) With metals (Table 19) proceeds differently, but these features of these acids will be explained somewhat later.

Table 19
Interaction products
simple substances with nitric and sulfuric acids

3. Inorganic and organic acids interact with basic and amphoteric oxides, provided that a soluble salt is formed:

4. Both those and other acids react with bases. Polybasic acids can form both medium and acidic salts (these are neutralization reactions):

5. The reaction between acids and salts takes place only if a gas or precipitate is formed:

The interaction of phosphoric acid Н 2 РО 4 with limestone will cease due to the formation on the surface of the last insoluble calcium phosphate Ca 3 (РO 4) 2 precipitate.

6. Esters form not only organic acids according to the general equation:

but also inorganic acids, such as nitric and sulfuric:

A similar reaction involving two and three hydroxo groups of cellulose during its nitration leads to the production of esters: di- and trinitrocellulose - the necessary substances for the production of smokeless gunpowder.

At the same time, some representatives of mineral and organic acids also have special properties.

The peculiarities of the properties of nitric HNO 3 and concentrated sulfuric H 2 SO 4 (conc.) Acids are due to the fact that when they interact with simple substances (metals and non-metals), nitrate and sulfate ions, rather than H + cations, will act as oxidants. It is logical to expect that as a result of such reactions, not hydrogen H2 is formed, but other substances are obtained: necessarily salt and water, as well as one of the reduction products of nitrate or sulfate ions, depending on the concentration of acids, the position of the metal in a series of voltages and reaction conditions (temperature, degree of fineness of metal, etc.).

It should be noted that the third product of the reaction of metals with these acids is often formed in a "bouquet" - a mixture with other products, but in Table 19 we have indicated the predominant products.

These features of the chemical behavior of HNO 3 and H 2 SO 4 (conc.) Clearly illustrate the thesis of the theory chemical structure about the mutual influence of atoms in molecules of substances. It can also be traced by the example of the properties of organic acids, for example, acetic and formic.

Acetic acid CH 3 COOH, like other carboxylic acids, contains a hydrocarbon radical in the molecule. In it, reactions of substitution of hydrogen atoms by halogen atoms are possible:

Under the influence of halogen atoms in the acid molecule, its degree of dissociation is greatly increased. For example, chloroacetic acid is almost 100 times stronger than acetic acid (why?).

Formic acid HCOOH, unlike acetic acid, does not have a hydrocarbon radical in the molecule. Instead, it contains a hydrogen atom, and therefore is a substance with a dual function - aldehyde acid and, unlike others carboxylic acids, gives the "silver mirror" reaction:

The resulting carbonic acid H 2 CO 3 decomposes into water and carbon dioxide, which in excess of ammonia is converted into ammonium bicarbonate.

Bases, amphoteric hydroxides

Foundations are complex substances consisting of metal atoms and one or more hydroxyl groups (-OH). General formula Me + y (OH) y, where y is the number of hydroxo groups equal to the oxidation state of the metal Me. The table shows the classification of the bases.

Properties of alkali hydroxides of alkali and alkaline earth metals

1. Aqueous solutions of alkalis are soapy to the touch, change the color of indicators: litmus - in blue, phenolphthalein - in raspberry.

2. Aqueous solutions dissociate:

3. Interact with acids, entering into an exchange reaction:

Multi-acid bases can give medium and basic salts:

4. React with acidic oxides, forming medium and acidic salts, depending on the basicity of the acid corresponding to this oxide:

5. Interact with amphoteric oxides and hydroxides:

a) fusion:

b) in solutions:

6. Interact with water-soluble salts if sediment or gas forms:

Insoluble bases (Cr (OH) 2, Mn (OH) 2, etc.) interact with acids and decompose when heated:

Amphoteric hydroxides

Amphoteric compounds are called compounds that, depending on the conditions, can be both donors of hydrogen cations and exhibit acidic properties, as well as their acceptors, i.e., exhibit basic properties.

Chemical properties of amphoteric compounds

1. Interacting with strong acids, they exhibit basic properties:

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

2. Interacting with alkalis - strong bases, they exhibit acidic properties:

Zn (OH) 2 + 2NaOH = Na 2 ( complex salt)

Al (OH) 3 + NaOH = Na ( complex salt)

Compounds are called complex in which at least one covalent bond is formed by the donor-acceptor mechanism.

The general method for obtaining bases is based on exchange reactions, with the help of which both insoluble and soluble bases can be obtained.

CuSO 4 + 2KON = Cu (OH) 2 ↓ + K 2 SO 4

K 2 CO 3 + Ba (OH) 2 = 2 KOH + BaCO 3 ↓

When soluble bases are obtained by this method, an insoluble salt precipitates.

When obtaining water-insoluble bases with amphoteric properties, an excess of alkali should be avoided, since dissolution of the amphoteric base may occur, for example:

АlСl 3 + 4КОН = К [Аl (ОН) 4] + 3КСl

In such cases, ammonium hydroxide is used to obtain hydroxides, in which amphoteric hydroxides do not dissolve:

АlСl 3 + 3NH 3 + ЗН 2 О = Аl (ОН) 3 ↓ + 3NH 4 Cl

Silver and mercury hydroxides decompose so easily that when you try to obtain them by an exchange reaction, oxides precipitate instead of hydroxides:

2AgNO 3 + 2KON = Ag 2 O ↓ + H 2 O + 2KNO 3

In industry, alkalis are usually obtained by electrolysis of aqueous solutions of chlorides.

2NaCl + 2Н 2 О → ϟ → 2NaOH + H 2 + Cl 2

Alkalis can also be obtained by reacting alkali and alkaline earth metals or their oxides with water.

2Li + 2H 2 O = 2LiOH + H 2

SrO + H 2 O = Sr (OH) 2

Acids

Acids are called complex substances, the molecules of which consist of hydrogen atoms that can be replaced by metal atoms, and acid residues. Under normal conditions, acids can be solid (phosphoric H 3 PO 4; silicon H 2 SiO 3) and liquid (pure liquid will be sulphuric acid H 2 SO 4).

Gases such as hydrogen chloride HCl, hydrogen bromide HBr, hydrogen sulfide H 2 S, in aqueous solutions form the corresponding acids. The number of hydrogen ions formed by each acid molecule during dissociation determines the charge of the acid residue (anion) and the basicity of the acid.

According to protolytic theory of acids and bases, proposed simultaneously by the Danish chemist Brønsted and the English chemist Lowry, an acid is called a substance splitting off with this reaction protons, a basis- a substance capable of take protons.

acid → base + H +

Based on such ideas, it is clear basic properties of ammonia, which, due to the presence of a lone electron pair at the nitrogen atom, effectively accepts a proton when interacting with acids, forming an ammonium ion through a donor-acceptor bond.

HNO 3 + NH 3 ⇆ NH 4 + + NO 3 -

acid base acid base

More general definition acids and bases suggested by the American chemist G. Lewis. He suggested that acid-base interactions are completely do not necessarily occur with proton transfer. In the determination of acids and bases according to Lewis, the main role in chemical reactions is assigned to electronic pairs.

Cations, anions or neutral molecules capable of accepting one or more pairs of electrons are called Lewis acids.

For example, aluminum fluoride AlF 3 is an acid, since it is capable of accepting an electron pair when interacting with ammonia.

AlF 3 +: NH 3 ⇆:

Cations, anions or neutral molecules capable of donating electron pairs are called Lewis bases (ammonia is a base).

Lewis's definition covers all acid-base processes that have been considered by previously proposed theories. The table compares the definitions of acids and bases currently used.

Nomenclature of acids

Since there are different definitions of acids, their classification and nomenclature are rather arbitrary.

According to the number of hydrogen atoms capable of elimination in an aqueous solution, acids are divided into monobasic(for example, HF, HNO 2), dibasic(H 2 CO 3, H 2 SO 4) and tribasic(H 3 PO 4).

By composition, the acid is divided into anoxic(HCl, H 2 S) and oxygenated(HClO 4, HNO 3).

Usually oxygenated acid names are made from the name of a non-metal with the addition of the endings -ka, -th, if the oxidation state of the non-metal is equal to the group number. As the oxidation state decreases, the suffixes change (in order of decreasing metal oxidation state): -some, true, -sweet:

If we consider the polarity of the hydrogen-non-metal bond within the period, one can easily relate the polarity of this bond with the position of the element in the Periodic Table. From metal atoms, which easily lose valence electrons, hydrogen atoms accept these electrons, forming a stable two-electron shell like the shell of a helium atom, and give ionic metal hydrides.

V hydrogen compounds elements of III-IV groups of the Periodic table boron, aluminum, carbon, silicon form covalent, weakly polar bonds with hydrogen atoms, not prone to dissociation. For elements of V-VII groups Periodic table within the period, the polarity of the non-metal-hydrogen bond increases with the charge of the atom, but the distribution of charges in the resulting dipole is different than in the hydrogen compounds of elements that tend to donate electrons. The atoms of non-metals, in which several electrons are needed to complete the electron shell, attract (polarize) a pair of bond electrons the stronger, the greater the charge of the nucleus. Therefore, in the series CH 4 - NH 3 - H 2 O - HF or SiH 4 - PH 3 - H 2 S - HCl bonds with hydrogen atoms, while remaining covalent, acquire a more polar character, and the hydrogen atom in the dipole of the element-hydrogen bond becomes more electropositive. If polar molecules end up in a polar solvent, electrolytic dissociation can occur.

Let us discuss the behavior of oxygen-containing acids in aqueous solutions. These acids have communication N-O-E and, naturally, the polarity of the Н-О bond is influenced by O-E communication... Therefore, these acids dissociate, as a rule, more easily than water.

H 2 SO 3 + H 2 O ⇆ H s O + + HSO 3

HNO 3 + H 2 O ⇆ H s O + + NO 3

Let's look at a few examples. properties of oxygen-containing acids, formed by elements that are capable of exhibiting different oxidation states. It is known that hypochlorous acidНСlO very weak hydrochloric acid HClO 2 also weak but stronger hypochlorous, hydrochloric acid HClO 3 strong. Perchloric acid НСlO 4 - one of the the strongest inorganic acids.

For dissociation by the acid type (with the elimination of the H ion), a rupture is required communication O-N... How can we explain the decrease in the strength of this bond in the series НСlO - НСlO 2 - НСlO 3 - НСClO 4? In this series, the number of oxygen atoms bound to the central chlorine atom increases. Each time a new bond of oxygen with chlorine is formed, the electron density is pulled from the chlorine atom, and therefore from the single O-Cl bond. As a result, the electron density partly leaves the O – H bond, which is weakened because of this.

Such a pattern - enhancement of acidic properties with an increase in the oxidation state of the central atom - characteristic not only for chlorine, but also for other elements. For example, nitric acid HNO 3, in which the oxidation state of nitrogen is +5, is stronger than nitrous acid HNO 2 (nitrogen oxidation state +3); sulfuric acid H 2 SO 4 (S +6) is stronger than sulfurous acid H 2 SO 3 (S +4).

Getting acids

1. Anoxic acids can be obtained with direct connection of non-metals with hydrogen.

H 2 + Cl 2 → 2HCl,

H 2 + S ⇆ H 2 S

2. Some oxygenated acids can be obtained the interaction of acidic oxides with water.

3. Both anoxic and oxygen-containing acids can be obtained on exchange reactions between salts and other acids.

BaBr 2 + H 2 SO 4 = BaSO 4 ↓ + 2HBr

CuSO 4 + H 2 S = H 2 SO 4 + CuS ↓

FeS + H 2 SO 4 (pa sb) = H 2 S + FeSO 4

NaCl (T) + H 2 SO 4 (conc) = HCl + NaHSO 4

AgNO 3 + HCl = AgCl ↓ + HNO 3

CaCO 3 + 2HBr = CaBr 2 + CO 2 + H 2 O

4. Some acids can be obtained using redox reactions.

H 2 O 2 + SO 2 = H 2 SO 4

3Р + 5HNO 3 + 2Н 2 O = ЗН 3 РО 4 + 5NO 2

can be divided into two types of reactions:

1) general for acids the reactions are associated with the formation of the hydronium ion H 3 O + in aqueous solutions;

2) specific(i.e. characteristic) reactions specific acids.

The hydrogen ion can enter into redox reactions, reducing to hydrogen, and in the compound reaction with negatively charged or neutral particles having lone pairs of electrons, i.e., in acid-base reactions.

The general properties of acids include the reactions of acids with metals in the range of voltages up to hydrogen, for example:

Zn + 2H + = Zn 2+ + H 2

Acid-base reactions include reactions with basic oxides and bases, as well as with medium, basic, and sometimes acidic salts.

2 CO 3 + 4HBr = 2CuBr 2 + CO 2 + 3H 2 O

Mg (HCO 3) 2 + 2HCl = MgCl 2 + 2CO 2 + 2H 2 O

2KHSO 3 + H 2 SO 4 = K 2 SO 4 + 2SO 2 + 2H 2 O

Note that polybasic acids dissociate stepwise, and at each subsequent step, dissociation is more difficult, therefore, with an excess of acid, acidic salts are most often formed, rather than average ones.

Ca 3 (PO 4) 2 + 4H 3 PO 4 = 3Ca (H 2 PO 4) 2

Na 2 S + H 3 PO 4 = Na 2 HPO 4 + H 2 S

NaOH + H 3 PO 4 = NaH 2 PO 4 + H 2 O

KOH + H 2 S = KHS + H 2 O

At first glance, the formation of acidic salts may seem surprising monobasic hydrofluoric (hydrofluoric) acid. However, this fact can be explained. Unlike all other hydrohalic acids, hydrofluoric acid in solutions is partially polymerized (due to the formation hydrogen bonds) and it may contain different particles (HF) X, namely H 2 F 2, H 3 F 3, etc.

A special case of acid-base balance - reactions of acids and bases with indicators, which change their color depending on the acidity of the solution. Indicators are used in qualitative analysis for the detection of acids and bases in solutions.

The most commonly used indicators are - litmus(v neutral environment purple, v sour - Red, v alkaline - blue), methyl orange(v sour environment Red, v neutral - orange, v alkaline - yellow), phenolphthalein(v strongly alkaline environment crimson red v neutral and acidic - colorless).

Specific properties different acids can be of two types: first, the reactions leading to the formation insoluble salts and secondly, redox transformations. If the reactions associated with the presence of the H + ion in them are common to all acids (qualitative reactions for the detection of acids), specific reactions are used as qualitative for individual acids:

Ag + + Cl - = AgCl (white precipitate)

Ba 2+ + SO 4 2- = BaSO 4 (white precipitate)

3Ag + + PO 4 3 - = Ag 3 PO 4 (yellow precipitate)

Some specific reactions of acids are due to their redox properties.

Anoxic acids in aqueous solution can only be oxidized.

2КМnO 4 + 16HСl = 5Сl 2 + 2КСl + 2МnСl 2 + 8Н 2 O

H 2 S + Br 2 = S + 2HBg

Oxygen-containing acids can be oxidized only if the central atom in them is in a lower or intermediate oxidation state, as, for example, in sulfurous acid:

H 2 SO 3 + Cl 2 + H 2 O = H 2 SO 4 + 2HCl

Many oxygen-containing acids, in which the central atom has the maximum oxidation state (S +6, N +5, Cr +6), exhibit the properties of strong oxidizing agents. Concentrated H 2 SO 4 is a strong oxidizing agent.

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

Pb + 4HNO 3 = Pb (NO 3) 2 + 2NO 2 + 2H 2 O

C + 2H 2 SO 4 (conc) = CO 2 + 2SO 2 + 2H 2 O

It should be remembered that:

Acid solutions react with metals in the electrochemical series of voltages to the left of hydrogen, subject to a number of conditions, the most important of which is the formation of a soluble salt as a result of the reaction. The interaction of HNO 3 and H 2 SO 4 (conc.) With metals proceeds differently.

Concentrated sulfuric acid passivates aluminum, iron, chromium in the cold.

In water, acids dissociate into hydrogen cations and anions of acid residues, for example:

Inorganic and organic acids interact with basic and amphoteric oxides, provided that a soluble salt is formed:

Both those and other acids react with bases. Polybasic acids can form both medium and acidic salts (these are neutralization reactions):

The reaction between acids and salts takes place only if a precipitate or gas is formed:

The interaction of H 3 PO 4 with limestone will cease due to the formation of the last insoluble precipitate Ca 3 (PO 4) 2 on the surface.

The peculiarities of the properties of nitric HNO 3 and concentrated sulfuric H 2 SO 4 (conc.) Acids are due to the fact that when they interact with simple substances (metals and non-metals), nitrate and sulfate ions, rather than H + cations, will act as oxidants. It is logical to expect that as a result of such reactions, not hydrogen H 2 is formed, but other substances are obtained: necessarily salt and water, as well as one of the reduction products of nitrate or sulfate ions, depending on the concentration of acids, the position of the metal in a series of voltages and reaction conditions (temperature, degree of fineness of metal, etc.).

These features of the chemical behavior of HNO 3 and H 2 SO 4 (conc.) Clearly illustrate the thesis of the theory of chemical structure on the mutual influence of atoms in molecules of substances.

The concepts of volatility and stability (stability) are often confused. Volatile acids are called acids, the molecules of which easily pass into a gaseous state, that is, they evaporate. For example, hydrochloric acid is a volatile but persistent, stable acid. The volatility of unstable acids cannot be judged. For example, non-volatile, insoluble silicic acid decomposes into water and SiO 2. Aqueous solutions of hydrochloric, nitric, sulfuric, phosphoric and a number of other acids have no color. An aqueous solution of chromic acid H 2 CrO 4 has a yellow color, manganic acid HMnO 4 - raspberry.

Reference material for passing the test:

Mendeleev table

Solubility table

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Slide captions:

Teacher: Grudinina Tatyana Viktorovna Lesson topic: Acids

Lesson objectives: To generalize and consolidate knowledge about the classification, nomenclature, properties of organic and inorganic acids Teach to explain the generality of the chemical properties of inorganic and organic acids Teach to correctly draw up the equations of reactions in molecular and ionic form

Determination of acids Acids in nature Classification of acids Chemical properties of acids Obtaining acids Using acids Lesson plan:

Acids are electrolytes, the dissociation of which produces only hydrated hydrogen ions (H 3 O +) as cations. 1. Determination of acids

In 1923. a protolithic theory was proposed by Bernsted-Lauri. Acids are molecules or ions that donate hydrogen cations H +. The H + cation is called a proton, so the theory is called protolytic. According to electronic theory acids and bases of the American chemist G.N. Lewis acids are reagents that are electron acceptors.

2. Acids in nature Acid rain (nitric, sulfuric acids) Acids in food (malic, oxalic, citric, lactic, butyric, coffee and others) "Chemical weapons" of animals and plants. When bitten, the ant injects poison containing formic acid. Nettles also use it.

The pedipalpid spider shoots a trickle of acetic acid at its enemies. Flat millipedes use a more terrible poison - hydrocyanic acid vapor. Amanita muscaria use ibotenic acid and its complex compound, muscimol. Destruction rocks and soil formation. Lichens can release acids that can turn granite into dust.

Vitamins: ascorbic, folic, orotic, pangamic, nicotine and others. Hyaluronic acid is the main ingredient in joint lubrication. Amino acids form proteins. Hydrochloric acid in the stomach activates the enzyme pepsinogen, which decomposes food proteins, and also destroys putrefactive microflora. Acids in the human body.

By composition: Oxygen-containing: H NO 3, H 2 SO 3; Oxygen-free: HCl, H 2 S. By basicity: (the basicity of an acid is determined by the number of cations that are formed during dissociation). Monobasic: HBr, HNO 2; Dibasic: H 2 S, H 2 SO 4; Polybasic: H 3 PO 4. Exercise. Name the acids and give them a classification: HClO 3, H 2 S, H 3 PO 4, HBr. 3. Classification of acids:

Interaction with metals located in the electrochemical range of metal voltages to hydrogen. 4. Chemical properties of acids: oxidizing agent, reducing agent, oxidizing magnesium acetate

Interaction with basic and amphoteric oxides. On one's own:

Interaction with soluble and insoluble bases. They can form medium and acidic salts. These are neutralization reactions. On its own: 1 mol (excess) 1 mol sodium hydrogen sulfate (acidic salt) 1 mol 2 mol sodium sulfate (medium salt)

Interaction with salts Strong acid is able to displace weak acid even from insoluble salt. On one's own:

Hydrochloric acid For dissolving scale and rust during nickel plating, chrome plating, zinc plating, etc. steel and cast iron products For descaling in steam boilers Hydrofluoric acid HF. The wood is impregnated to protect it from termites and other insects. Application of acids

Sulfuric acid For the production of phosphoric and nitrogen fertilizers In the production of explosives Artificial fibers Dyes Plastics Filling in batteries

Nitric acid Production of nitrogen fertilizers Explosives Medicinal substances Dyes Plastics Artificial fibers

Task 1. Write formulas and characterize acids based on their classification: silicic acid, hydrofluoric acid. Task 2. What substances will phosphoric acid react with: K, SO 2, Na 2 SO 4, Na 2 CO 3, MgO, Ag, Ba (OH) 2. Anchoring

Task 1. H 2 SiO 3 - oxygen-containing, dibasic, insoluble, weak HF - anoxic, monobasic, soluble, weak Task 2. Answers

Thank you for the lesson!!!

Acids complex substances are called, the molecules of which include hydrogen atoms that can be replaced or exchanged for metal atoms and an acid residue.

According to the presence or absence of oxygen in the molecule, acids are divided into oxygen-containing(H 2 SO 4 sulfuric acid, H 2 SO 3 sulfurous acid, HNO 3 nitric acid, H 3 PO 4 phosphoric acid, H 2 CO 3 carbonic acid, H 2 SiO 3 silicic acid) and anoxic(HF hydrofluoric acid, HCl hydrochloric acid (hydrochloric acid), HBr hydrobromic acid, HI hydroiodic acid, H 2 S hydrosulfuric acid).

Depending on the number of hydrogen atoms in the acid molecule, there are monobasic (with 1 H atom), dibasic (with 2 H atoms) and tribasic (with 3 H atoms). For example, nitric acid HNO 3 is monobasic, since its molecule contains one hydrogen atom, sulfuric acid H 2 SO 4 – dibasic, etc.

There are very few inorganic compounds containing four hydrogen atoms that can be replaced by a metal.

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 be from a group of atoms (-SO 3, -PO 4, -SiO 3) - these are complex residues.

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

H 2 SO 4 + CuCl 2 → CuSO 4 + 2 HCl

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

H 2 SO 4 - H 2 O → SO 3. Anoxic acids have no anhydrides.

The name of the acid is derived from the name of the acid-forming element (acid-forming agent) with the addition of the endings "naya" and less often "vay": H 2 SO 4 - sulfuric; H 2 SO 3 - coal; H 2 SiO 3 - silicon, etc.

The element can form several oxygen acids. In this case, the indicated endings in the name of acids will be when the element exhibits the highest valence (in the acid molecule there is a large content of oxygen atoms). If the element exhibits the lowest valence, the ending in the name of the acid will be "true": HNO 3 - nitric, HNO 2 - nitrogenous.

Acids can be obtained by dissolving anhydrides in water. In case 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 anoxic acids. Anoxic acids are also obtained by direct synthesis from hydrogen and non-metal, followed by dissolution of the resulting compound in water:

H 2 + Cl 2 → 2 HCl;

H 2 + S → H 2 S.

Solutions of the obtained gaseous substances HCl and H 2 S are acids.

Under normal conditions, acids are either liquid or solid.

Chemical properties of acids

A solution of acids affects the indicators. All acids (except for silicic acid) are readily soluble in water. Special substances - indicators allow you to determine the presence of acid.

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

Interact with bases with the formation of water and salt, which contains an unchanged acidic residue (neutralization reaction):

H 2 SO 4 + Ca (OH) 2 → CaSO 4 + 2 H 2 O.

Interact with based oxides with the formation of water and salt (neutralization reaction). The salt contains an acidic residue of the acid that was used in the neutralization reaction:

H 3 PO 4 + Fe 2 O 3 → 2 FePO 4 + 3 H 2 O.

Interact with metals. For the interaction of acids with metals, certain conditions must be met:

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

2. the acid must be strong enough (that is, capable of giving off hydrogen ions H +).

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

Zn + 2HCl → ZnCl 2 + H 2;

Cu + 4HNO 3 → CuNO 3 + 2 NO 2 + 2 H 2 O.

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