What are acids? Acids: classification and chemical properties

Acids- complex substances consisting of one or more hydrogen atoms that can be replaced by metal atoms and acidic residues.

Classification of acids

1. By the number of hydrogen atoms: number of hydrogen atoms ( n ) determines the basicity of acids:

n= 1 monobase

n= 2 dibase

n= 3 tribase

2. By composition:

a) Table of oxygen-containing acids, acid residues and corresponding acid oxides:

b) Table of oxygen-free acids

Physical properties of acids

Many acids, such as sulfuric, nitric, and hydrochloric, are colorless liquids. solid acids are also known: orthophosphoric, metaphosphoric HPO 3, boric H 3 BO 3 . Almost all acids are soluble in water. An example of an insoluble acid is silicic acid H2SiO3 . Acid solutions have a sour taste. For example, many fruits are given a sour taste by the acids they contain. Hence the names of acids: citric, malic, etc.

Methods for producing acids

Chemical properties of acids

1. Change the color of the indicators

2. React with metals in the activity series up to H 2

(excl. HNO 3 -Nitric acid)

Video "Interaction of acids with metals"

Me + ACID = SALT + H 2 (r. substitution)

Zn + 2 HCl = ZnCl 2 + H 2

3. With basic (amphoteric) oxides – metal oxides

Video "Interaction of metal oxides with acids"

Fur x O y + ACID = SALT + H 2 O (exchange ruble)

4. React with bases – neutralization reaction

ACID + BASE= SALT+ H 2 O (exchange ruble)

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

5. React with salts of weak, volatile acids - if acid forms, precipitates or gas evolves:

2 NaCl (tv.) + H 2 SO 4 (conc.) = Na 2 SO 4 + 2HCl ( R . exchange )

Video "Interaction of acids with salts"

6. Decomposition of oxygen-containing acids when heated

(excl. H 2 SO 4 ; H 3 P.O. 4 )

ACID = ACID OXIDE + WATER (r. expansion)

Remember!Unstable acids (carbonic and sulfurous acids) - decompose into gas and water:

H 2 CO 3 ↔ H 2 O + CO 2

H 2 SO 3 ↔ H 2 O + SO 2

Hydrogen sulfide acid in products released as gas:

CaS + 2HCl = H 2 S+CaCl2

ASSIGNMENT TASKS

No. 1. Distribute the chemical formulas of acids in a table. Give them names:

LiOH, Mn 2 O 7, CaO, Na 3 PO 4, H 2 S, MnO, Fe (OH) 3, Cr 2 O 3, HI, HClO 4, HBr, CaCl 2, Na 2 O, HCl, H 2 SO 4, HNO 3, HMnO 4, Ca (OH) 2, SiO 2, Acids

Bes-sour-

native

Oxygen-containing

soluble

insoluble

one-

basic

two-basic

three-basic

No. 2. Write down the reaction equations:

Ca + HCl

Na+H2SO4

Al+H2S

Ca+H3PO4
Name the reaction products.

No. 3. Write down reaction equations and name the products:

Na 2 O + H 2 CO 3

ZnO + HCl

CaO + HNO3

Fe 2 O 3 + H 2 SO 4

No. 4. Write down equations for the reactions of acids with bases and salts:

KOH + HNO3

NaOH + H2SO3

Ca(OH) 2 + H 2 S

Al(OH) 3 + HF

HCl + Na 2 SiO 3

H2SO4 + K2CO3

HNO3 + CaCO3

Name the reaction products.

EXERCISES

Trainer No. 1. "Formula and names of acids"

Trainer No. 2. "Establishing correspondence: acid formula - oxide formula"

Safety precautions - First aid in case of acid contact with skin

Safety precautions -

Acids 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(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 oxygen-free(HF hydrofluoric acid, HCl hydrochloric acid (hydrochloric acid), HBr hydrobromic acid, HI hydroiodic acid, H 2 S 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). 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.

Acidic residues may consist of one atom (-Cl, -Br, -I) - these are simple acidic residues, or they may consist of a group of atoms (-SO 3, -PO 4, -SiO 3) - these are complex residues.

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

H 2 SO 4 + CuCl 2 → CuSO 4 + 2 HCl

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

H 2 SO 4 – H 2 O → SO 3. Anoxic acids do not have anhydrides.

Acids get their name from the name of the acid-forming element (acid-forming agent) with the addition of the endings “naya” and less often “vaya”: 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 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”: HNO 3 - nitric, HNO 2 - nitrogenous.

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:

H 2 + Cl 2 → 2 HCl;

H 2 + S → H 2 S.

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

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

Chemical properties of acids

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.

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

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

Interact with base oxides with the formation of water and salt (neutralization reaction). The salt contains the acid 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 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;

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 → ZnCl 2 + H 2 ;

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

Still have questions? Want to know more about acids?
To get help from a tutor -.
The first lesson is free!

blog.site, when copying material in full or in part, a link to the original source is required.

Acids are complex chemical compounds that contain one or more hydrogen atoms and an acid residue. The word “acid” is related in meaning to the word “sour”, since they have a common root. It follows that solutions of all acids have a sour taste. Despite this, not all acid solutions can be tasted, since some of them are caustic and poisonous solutions. Acids, due to their properties, are widely used in everyday life, medicine, industry and other areas.

History of the study of acids

Acids have been known to mankind since ancient times. Obviously, the first acid obtained by man as a result of fermentation (oxidation in air) of wine was acetic acid. Even then, some properties of acids were known, which were used to dissolve metals and obtain mineral pigments, for example: lead carbonate. During the Middle Ages, alchemists “discovered” new acids of mineral origin. The first attempt to unite all acids with a common property was made by the physical chemist Svante Arrhenius (Stockholm, 1887). Currently, science adheres to the Brønsted-Lowry and Lewis theory of acids and bases, founded in 1923.

Oxalic acid (ethanedioic acid) is a strong organic acid and has all the properties of carboxylic acids. It is colorless crystals that are readily soluble in water, incompletely soluble in ethyl alcohol and insoluble in benzene. In nature, oxalic acid is found in plants such as sorrel, carom, rhubarb, etc.

Application:

In the chemical industry (for the production of ink, plastics);

In metallurgy (for cleaning rust, scale);

In the textile industry (for dyeing furs and fabrics);

In cosmetology (whitening agent);

To purify and reduce water hardness;

In medicine;

In pharmacology.

Oxalic acid is poisonous and toxic; if it comes into contact with the skin, mucous membranes and respiratory organs, it causes irritation.

In our online store you can buy oxalic acid for only 258 rubles.

Salicylic acid is a crystalline powder that dissolves well in alcohol but poorly in water. It was first obtained from willow bark (where it got its name) by chemist Raphael Piria in 1838 in Italy.

Widely used:

In pharmacology;

In medicine (anti-inflammatory, wound healing, antiseptic for the treatment of burns, warts, acne, eczema, hair loss, profuse sweating, ichthyosis, calluses, pityriasis versicolor, etc.);

In cosmetology (as an exfoliant, antiseptic);

In the food industry (when canning products).

In case of an overdose, this acid kills beneficial bacteria and dries out the skin, which can cause acne. It is not recommended to use it as a cosmetic product more than once a day.

Salicylic acid price for only 308 rubles.

Boric acid (orthoboric acid) has the appearance of a shiny crystalline powder, greasy to the touch. It is a weak acid and is better soluble in hot water and salt solutions, less soluble in cold water and mineral acids. It is found in nature in the form of the mineral sassolina, in mineral waters, natural brines and hot springs.

Applicable:

In industry (in the production of enamel, cement, detergents);

In cosmetology;

In agriculture (as a fertilizer);

In laboratories;

In pharmacology and medicine (antiseptic);

In everyday life (to combat insects);

In cooking (for canning and as a food additive).

Buy boric acid in Moscow for only 114 rubles.

Citric acid is a food additive (E330/E333) in the form of a white crystalline substance. It dissolves well in both water and ethyl alcohol. In nature, it is found in many citrus fruits, berries, pine needles, etc. Citric acid was first obtained from the juice of unripe lemons by pharmacist Karl Scheele (Sweden, 1784).

Citric acid has found its application:

In the food industry (as an ingredient in seasonings, sauces, semi-finished products);

In the oil and gas industry (during well drilling);

In cosmetology (in creams, shampoos, lotions, bath products);

In pharmacology;

In everyday life (in the manufacture of detergents).

However, if a concentrated solution of citric acid comes into contact with the skin, mucous membrane of the eyes or tooth enamel, it can cause harm.

Buy citric acid on our website from 138 rubles.

Lactic acid is a clear liquid with a slight odor, which is classified as a food additive (E270). For the first time, lactic acid, as well as citric acid, was obtained by the chemist Karl Scheele. Currently, it is obtained by fermenting milk, wine or beer.

Application:

In industry (for making cheese, mayonnaise, yogurt, kefir, confectionery);

In agriculture (for preparing feed);

In veterinary medicine (antiseptic);

In cosmetology (whitening agent).

When working with lactic acid, you must take precautions, as it can cause dry skin, necrosis of the mucous membrane of the eyes, etc.

Buy lactic acid right now for 129 rubles.

The retail chemical reagents store in Moscow "Prime Chemicals Group" is an excellent selection of laboratory equipment and chemical reagents at affordable prices.

Let me briefly remind you, using specific examples, of how salts should be called correctly.

Example 1. The salt K 2 SO 4 is formed by a sulfuric acid residue (SO 4) and metal K. Salts of sulfuric acid are called sulfates. K 2 SO 4 - potassium sulfate.

Example 2. FeCl 3 - the salt contains iron and a hydrochloric acid residue (Cl). Name of salt: iron (III) chloride. Please note: in this case we must not only name the metal, but also indicate its valence (III). In the previous example, this was not necessary, since the valence of sodium is constant.

Important: the name of the salt should indicate the valence of the metal only if the metal has a variable valency!

Example 3. Ba(ClO) 2 - the salt contains barium and the remainder of hypochlorous acid (ClO). Salt name: barium hypochlorite. The valency of the metal Ba in all its compounds is two; it does not need to be indicated.

Example 4. (NH 4) 2 Cr 2 O 7. The NH 4 group is called ammonium, the valence of this group is constant. Name of salt: ammonium dichromate (dichromate).

In the above examples we only encountered the so-called. medium or normal salts. Acidic, basic, double and complex salts, salts of organic acids will not be discussed here.

If you are interested not only in the nomenclature of salts, but also in the methods of their preparation and chemical properties, I recommend that you refer to the relevant sections of the chemistry reference book: "

These are substances that dissociate in solutions to form hydrogen ions.

Acids are classified by their strength, by their basicity, and by the presence or absence of oxygen in the acid.

By strengthacids are divided into strong and weak. The most important strong acids are nitric HNO 3, sulfuric H2SO4, and hydrochloric HCl.

According to the presence of oxygen distinguish between oxygen-containing acids ( HNO3, H3PO4 etc.) and oxygen-free acids ( HCl, H 2 S, HCN, etc.).

By basicity, i.e. According to the number of hydrogen atoms in an acid molecule that can be replaced by metal atoms to form a salt, acids are divided into monobasic (for example, HNO 3, HCl), dibasic (H 2 S, H 2 SO 4), tribasic (H 3 PO 4), etc.

The names of oxygen-free acids are derived from the name of the non-metal with the addition of the ending -hydrogen: HCl - hydrochloric acid, H2S e - hydroselenic acid, HCN - hydrocyanic acid.

The names of oxygen-containing acids are also formed from the Russian name of the corresponding element with the addition of the word “acid”. In this case, the name of the acid in which the element is in the highest oxidation state ends in “naya” or “ova”, for example, H2SO4 - sulfuric acid, HClO4 - perchloric acid, H3AsO4 - arsenic acid. With a decrease in the oxidation degree of the acid-forming element, the endings change in the following sequence: “ovate” ( HClO3 - perchloric acid), “solid” ( HClO2 - chlorous acid), “ovate” ( H O Cl - hypochlorous acid). If an element forms acids while being in only two oxidation states, then the name of the acid corresponding to the lowest oxidation state of the element receives the ending “iste” ( HNO3 - Nitric acid, HNO2 - nitrous acid).

Table - The most important acids and their salts

Obtaining acids

1. Oxygen-free acids can be obtained by direct combination of non-metals with hydrogen:

H 2 + Cl 2 → 2HCl,

H 2 + S H 2 S.

2. Oxygen-containing acids can often be obtained by directly combining acid oxides with water:

SO 3 + H 2 O = H 2 SO 4,

CO 2 + H 2 O = H 2 CO 3,

P 2 O 5 + H 2 O = 2 HPO 3.

3. Both oxygen-free and oxygen-containing acids can be obtained by 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,

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

4. In some cases, redox reactions can be used to produce acids:

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

3P + 5HNO3 + 2H2O = 3H3PO4 + 5NO.

Chemical properties of acids

1. The most characteristic chemical property of acids is their ability to react with bases (as well as basic and amphoteric oxides) to form salts, for example:

H 2 SO 4 + 2NaOH = Na 2 SO 4 + 2H 2 O,

2HNO 3 + FeO = Fe(NO 3) 2 + H 2 O,

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

2. The ability to interact with some metals in the voltage series up to hydrogen, with the release of hydrogen:

Zn + 2HCl = ZnCl 2 + H 2,

2Al + 6HCl = 2AlCl3 + 3H2.

3. With salts, if a slightly soluble salt or volatile substance is formed:

H 2 SO 4 + BaCl 2 = BaSO 4 ↓ + 2HCl,

2HCl + Na 2 CO 3 = 2NaCl + H 2 O + CO 2,

2KHCO 3 + H 2 SO 4 = K 2 SO 4 +2SO 2+ 2H 2 O.

Note that polybasic acids dissociate stepwise, and the ease of dissociation at each step decreases; therefore, for polybasic acids, instead of medium salts, acidic salts are often formed (in the case of an excess of the reacting acid):

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.

4. A special case of acid-base interaction is the reaction of acids with indicators, leading to a change in color, which has long been used for the qualitative detection of acids in solutions. So, litmus changes color in an acidic environment to red.

5. When heated, oxygen-containing acids decompose into oxide and water (preferably in the presence of a water-removing agent P2O5):

H 2 SO 4 = H 2 O + SO 3,

H 2 SiO 3 = H 2 O + SiO 2.

M.V. Andryukhova, L.N. Borodina