Hydrochloric acid (hydrochloric acid, an aqueous solution of hydrogen chloride), known as HCl, is a caustic chemical compound. Since ancient times, people have been using this colorless liquid for various purposes, which emits a light smoke in the open air.

Properties of a chemical compound

HCl is used in various areas of human activity. It dissolves metals and their oxides, is absorbed in benzene, ether and water, and does not destroy fluoroplastic, glass, ceramics and graphite. Its safe use is possible when stored and operated in the correct conditions, in compliance with all safety standards.

Chemically pure (CP) hydrochloric acid is formed during gaseous synthesis from chlorine and hydrogen, giving hydrogen chloride. It is absorbed in water, resulting in a solution containing 38-39% HCl at +18 C. An aqueous solution of hydrogen chloride is used in various areas of human activity. The price of chemically pure hydrochloric acid is variable and depends on many components.

Areas of application of aqueous hydrogen chloride solution

Usage of hydrochloric acid has become widespread due to its chemical and physical properties:

• in metallurgy, in the production of manganese, iron and zinc, technological processes, metal purification;
• in galvanoplasty - during etching and pickling;
• in the production of soda water to regulate acidity, in the manufacture alcoholic drinks and syrups in the food industry;
• for leather processing in light industry;
• when purifying non-drinking water;
• for optimization of oil wells in the oil industry;
• in radio engineering and electronics.

Hydrochloric acid (HCl) in medicine

The most famous property of hydrochloric acid solution is the equalization of the acid-base balance in the human body. Low stomach acidity is treated with a weak solution or drugs. This optimizes the digestion of food and helps fight germs and bacteria that penetrate from the outside. HCl hydrochloric acid helps normalize low levels of gastric acidity and optimizes protein digestion.

Oncology uses HCl to treat tumors and slow down their progression. Hydrochloric acid preparations are prescribed for the prevention of stomach cancer, rheumatoid arthritis, diabetes mellitus, asthma, urticaria, cholelithiasis and others. IN folk medicine Hemorrhoids are treated with a weak acid solution.

You can find out more about the properties and types of hydrochloric acid.

GOST 3118-77
(ST SEV 4276-83)

Group L51

STATE STANDARD OF THE USSR UNION

Reagents

HORRIATIC ACID

Specifications

Reagents. Hydrochloric acid.
Specifications

OKP 26 1234 0010 07

Date of introduction 1979-01-01

ENTERED INTO EFFECT by resolution State Committee standards of the Council of Ministers of the USSR dated December 22, 1977 N 2994

INSTEAD GOST 3118-67

REISSUE (January 1997) with Amendment No. 1, approved in November 1984 (IUS 2-85)

The validity period was lifted by decision of the Interstate Council for Standardization, Metrology and Certification (IUS 4-94)


This standard applies to the reagent - hydrochloric acid (aqueous solution of hydrogen chloride), which is a colorless liquid with a pungent odor, fuming in air; miscible with water, benzene and ether. The acid density is 1.15-1.19 g/cm.

The technical level indicators established by this standard are provided for the first quality category.

Formula: HCl.

Molecular mass (according to international atomic masses 1971) - 36.46.

The standard fully complies with ST SEV 4276-83.

1. TECHNICAL REQUIREMENTS

1. TECHNICAL REQUIREMENTS

1.1. Hydrochloric acid must be manufactured in accordance with the requirements of this standard according to technological regulations approved in the prescribed manner.

1.2. In terms of chemical indicators, hydrochloric acid must meet the requirements and standards specified in the table.

Note. Hydrochloric acid with the standards indicated in brackets may be produced until 01/01/95.

2a. SAFETY REQUIREMENTS

2a.1. Hydrochloric acid belongs to substances of hazard class III (GOST 12.1.007-76). The maximum permissible concentration of hydrogen chloride in the air of the working area is 5 mg/m. The acid has a cauterizing effect on the mucous membranes and skin, and severely irritates the respiratory tract.

2a.2. When working with the drug, you should use individual means protection, as well as observe the rules of personal hygiene and prevent the drug from getting on the mucous membranes, skin, and inside the body.

2a.3. The premises in which work with the drug is carried out must be equipped with general supply and exhaust mechanical ventilation; drug analysis should be carried out in a laboratory fume hood.

2a.4. Hydrochloric acid is a non-flammable and non-flammable liquid.

Section 2a.

2. ACCEPTANCE RULES

2.1. Acceptance rules - according to GOST 3885-73.

2.2. The manufacturer determines the mass fraction of ammonium salts, arsenic and sulfites periodically in every tenth batch.

3. METHODS OF ANALYSIS

3.1a. General instructions for conducting analysis - according to the technical documentation.

(Introduced additionally, Amendment No. 1).

3.1. Samples are taken according to GOST 3885-73. The mass of the average sample must be at least 4500 g (3900 cm).

For analysis, hydrochloric acid is taken with a safe pipette or graduated cylinder in accordance with the density with an error of no more than 1% (by volume).

3.2. Defining Appearance

25 cm of the drug is placed in a cylinder (with a ground stopper) with a capacity of 25 cm and compared in transmitted light along the diameter of the cylinder with the same volume of distilled water (GOST 6709-72) placed in the same cylinder.

The drug must be chemically pure and pure for analysis, colorless, transparent and free of suspended particles.

For a pure preparation, a yellowish color is allowed.

(Changed edition, Amendment No. 1).

3.3. Determination of the mass fraction of hydrochloric acid

3.3.1. Reagents and solutions

Distilled water according to GOST 6709-72.

Mixed indicator, solution of methyl red and methylene blue; prepared according to GOST 4919.1-77.

Sodium hydroxide according to GOST 4328-77, solution concentration (NaOH) = 1 mol/dm (1 N); prepared according to GOST 25794.1-83.

3.3.2. Carrying out analysis

In a conical flask with a capacity of 200-250 cm3, containing 50 cm3 of water, place from 1.2000 to 1.4000 g of the drug, weighed using a Lunge pipette, and mix thoroughly. Add 0.2 cm of mixed indicator solution and titrate with sodium hydroxide solution until the violet-red color changes to green.

3.3.3. Processing the results

The mass fraction of hydrochloric acid () in percent is calculated using the formula

where is the volume of sodium hydroxide solution with a concentration of exactly 1 mol/dm3, used for titration, cm;

0.03646 - mass of hydrogen chloride corresponding to 1 cm of sodium hydroxide solution with a concentration of exactly 1 mol/dm, g;

- weight of the drug sample, g.

The result of the analysis is taken as the arithmetic mean of two parallel determinations, the permissible differences between which are confidence probability= 0.95 should not exceed 0.2%.

It is allowed to determine the mass fraction of hydrochloric acid with methyl orange or methyl red.

In case of disagreement in the assessment of the mass fraction of hydrochloric acid, the analysis is carried out with a mixed indicator.

(Changed edition, Amendment No. 1)

3.4. Determination of the mass fraction of the residue after calcination (in the form of sulfates) is carried out according to ST SEV 434-77*. In this case, 200 g (170 cm) of the drug for the norm of 0.0005% and 100 g (85 cm) of the drug for the norm of 0.001; 0.002 and 0.005% are placed in a platinum or quartz cup, pre-calcined to constant mass and weighed with an error of no more than 0.0002 g, evaporated in a water bath in portions of up to 1-2 cm, then 0.1-0.5 cm of sulfuric acid is added ( GOST 4204-77). Next, the determination is carried out according to ST SEV 434-77*.

(Changed edition, Amendment No. 1).
_______________
* GOST 27184-86 is valid. - Note "CODE".

3.5. Determination of the mass fraction of sulfites

3.5.1. Reagents and solutions

Distilled water, not containing oxygen; prepared according to GOST 4517-87.

Iodine according to GOST 4159-79, solution concentration (1/2 J) = 0.01 mol/dm (0.01 N), freshly prepared; prepared according to GOST 25794.2-83.

Potassium iodide according to GOST 4232-74, 10% solution; prepared according to GOST 4517-87.

Hydrochloric acid according to this standard.

Soluble starch according to GOST 10163-76, 0.5% solution, freshly prepared.

3.5.2. Carrying out analysis

Place 400 cm of water in a conical flask with a capacity of 500 cm, add 1 cm of potassium iodide solution, 5 cm of hydrochloric acid and 2 cm of starch solution.

The solution is stirred and iodine solution is added dropwise until a bluish color appears. Half of the resulting solution is placed in another conical flask with a capacity of 500 cm3.

100 g (85 cm) of the analyzed drug is placed in one of the flasks in portions with stirring and cooling in an ice water bath, and the same amount of water is added to the other (reference solution).

The color of solutions is compared in transmitted light against the background of milk glass.

If the analyzed solution turns out to be colorless or its color is weaker than the color of the reference solution, then the drug contains an admixture of a reducing agent. In this case, the solution is immediately titrated from a microburette with an iodine solution until the initial bluish color

3.5.1, 3.5.2. (Changed edition, Amendment No. 1).

3.5.3. Processing the results

The mass fraction of sulfites () in percent is calculated using the formula

where is the volume of iodine solution with a concentration of exactly 0.01 mol/dm3 used for titration, cm;

0.00040 - mass of sulfites corresponding to 1 cm of iodine solution with a concentration of exactly 0.01 mol/dm, g.

The result of the analysis is taken as the arithmetic mean of two parallel determinations, the permissible differences between which, at a confidence probability = 0.95, should not exceed 20% relative to the calculated concentration.

(Introduced additionally, Amendment No. 1).

3.6. Determination of the mass fraction of sulfates

The determination is carried out according to GOST 10671.5-74. In this case, 10 g (8.5 cm) of the drug is placed in a porcelain or platinum cup, 2 cm of a 1% solution of sodium carbonate (GOST 83-79) is added, carefully mixed and evaporated to dryness in a water bath, the dry residue is dissolved in water and transfer the solution to a conical flask with a capacity of 50 cm (with a 25 cm mark), bring the volume of the solution to the mark with water and mix. If the solution is cloudy, filter it through a dense ashless filter, thoroughly washed hot water. Next, the determination is carried out using the phototurbidimetric or visual nephelometric method (method 1).

The drug is considered to comply with the requirements of this standard if the mass of sulfates does not exceed:

for the drug chemically pure - 0.020 mg;

for the drug pure for analysis - 0.020 (0.050) mg;

for the drug pure - 0.050 mg (0.100 mg).

The mass of sulfates indicated in brackets is established for standards in force before 01/01/95.

In case of disagreement in the assessment of the mass fraction of sulfates, the determination is carried out using the phototurbidimetric method; in this case, the mass of a sample of the chemically pure preparation is should be 30 g (25.5 cm).

(Changed edition, Amendment No. 1).

3.7. Determination of the mass fraction of free chlorine with -tolidine (carried out only in the absence of sulfites)

3.7.1. Equipment, reagents and solutions

Photoelectric colorimeter.

Hydrochloric acid according to this standard, not containing free chlorine (prepared by boiling for 5 minutes), concentrated and 3% solution.

-tolidine, 0.1% solution in 3% solution of hydrochloric acid, not containing chlorine.

A solution containing chlorine; prepared according to GOST 4212-76. By appropriate dilution, prepare a solution containing 0.01 mg of chlorine per 1 cm3.

3.7.2. Construction of a calibration graph

Prepare 5 reference solutions. To do this, solutions containing 0.01 in 50 cm, respectively, are placed in volumetric flasks with a capacity of 100 cm each; 0.02; 0.03; 0.04 and 0.05 mg Cl.

At the same time, prepare a control solution that does not contain free chlorine.

To each solution add 1 ml of α-tolidine solution, 10 ml of concentrated hydrochloric acid, adjust the volume of the solution to the mark with water and mix. After 5 minutes, the optical densities of the reference solutions are measured relative to the control solution in cuvettes with a light-absorbing layer thickness of 30 mm at a wavelength of 413 nm. Measurement of the optical density of reference solutions and analyzed solutions must be carried out within 20 minutes.

Based on the data obtained, a calibration graph is constructed.

3.7.3. Carrying out analysis

20 g (17 ml) of the drug is placed in a 100 ml volumetric flask containing 50 ml of water and 1 ml of -tolidine solution. The volume of the solution is adjusted to the mark with water and mixed. After 5 minutes, measure the optical density of the analyzed solution relative to the control solution in the same way as when constructing a calibration graph. The measurement should be carried out no more than 20 minutes. Based on the obtained optical density value, using the calibration graph, the content of free chlorine in the analyzed drug solution is determined.

The preparation is considered to comply with the requirements of this standard if the mass of free chlorine does not exceed:







If the mass fraction of iron in the preparation is less than 0.0001%, it is allowed to carry out the determination with potassium iodide and extraction with chloroform according to clause 3.8.

3.7.1-3.7.3. (Changed edition, Amendment No. 1).

3.8. Determination of the mass fraction of free chlorine by extraction method (carried out only in the absence of sulfites)

3.8.1. Reagents and solutions

Distilled water according to GOST 6709-72.

Iodine according to GOST 4159-79, 0.01 n. solution, freshly prepared.

Potassium iodide according to GOST 4232-74, chemical grade, 10% solution.

Sodium phosphate disubstituted 12-water according to GOST 4172-76, chemical grade, saturated solution.

Chloroform.

3.8.2. Carrying out analysis

70 g (60 cm) of the drug is placed in a separating funnel with a capacity of 200 cm, 20 cm of water, 2 cm of disubstituted sodium phosphate solution, 2 cm of potassium iodide solution are added, mixed and after 5 minutes, 5.5 cm of chloroform is added. The solution is shaken vigorously for 30 s. After separation, the chloroform layer of the analyzed solution is poured into a 10 cm test tube (with a ground-in stopper).

The drug is considered to comply with the requirements of this standard if the pink color of the chloroform layer of the analyzed solution is not more intense than the pink color of the chloroform layer of the solution prepared simultaneously with the analyzed solution and containing:

for the drug, chemically pure - 0.05 cm of iodine solution;

for the drug, pure for analysis - 0.05 cm of iodine solution;

for the preparation pure - 0.1 cm of iodine solution;

35 g (30 ml) of the drug, 10 ml of water, 1 ml of sodium phosphate solution, 1 ml of potassium iodide solution and 5 ml of chloroform.

1 cm is exactly 0.01 N., iodine solution corresponds to 0.00035 g Cl.

In case of disagreement in the assessment of the mass fraction of chlorine, the analysis is carried out with

Tolidin.

3.9. Determination of the mass fraction of ammonium salts

3.9.1. Reagents and solutions

Litmus paper.

Distilled water according to GOST 6709-72.

Sodium hydroxide, 20% solution without NH; prepared according to GOST 4517-87.

Nessler's reagent; prepared according to GOST 4517-87.

A solution containing NH; prepared according to GOST 4212-76.

3.9.2. Carrying out analysis

1.6 g (1.3 cm) of the drug containing 20 cm of water is placed in a conical flask with a capacity of 100 cm (with a mark at 50 cm), carefully neutralized using litmus paper with a solution of sodium hydroxide; bring the volume of the solution to the mark with water, mix and transfer the solution into a cylinder with a ground stopper. 2 cm of Nessler's reagent is added to the solution and mixed again.

The drug is considered to comply with the requirements of this standard if the observed color of the analyzed solution after 5 minutes is not more intense than the color of the reference solution prepared simultaneously with the analyzed solution and containing in the same volume:

for the drug chemically pure - 0.005 mg NH;

for the drug pure for analysis - 0.005 mg NH;

for the drug pure - 0.005 mg NH;

the amount of sodium hydroxide solution used to neutralize the analyzed solution, and 2 cm of Nessle’s reagent

3.10. The determination of the mass fraction of iron is carried out according to GOST 10555-75 using the 2.2"-dipyridyl or sulfosalicylic method.

(Changed edition, Amendment No. 1).

3.10.1. 2.2"-dipyridyl method

20 g (17 cm) of a chemically pure drug, 10 g (8.5 cm) of a pure drug for analysis and 2 g (1.7 cm) of a pure drug are placed in a platinum cup and evaporated to dryness in a water bath. The residue after evaporation is dissolved in 0.5 cm of hydrochloric acid, transferred to a volumetric flask with a capacity of 100 cm and the volume of the solution is adjusted to 40 cm with water. Next, the determination is carried out according to GOST 10555-75.



for the drug chemically pure - 0.01 mg;

for the drug pure for analysis - 0.01 mg;

for the drug pure - 0.006 (0.01) mg.

3.10.2. Sulfosalicylic method

10 g (8.5 cm) of the drug is placed in a conical flask with a capacity of 100 cm (with a 50 cm mark) and, while cooling, carefully neutralized dropwise with a 10% ammonia solution on litmus paper, then the determination is carried out according to GOST 10555-75.

The drug is considered to comply with the requirements of this standard if the mass of iron does not exceed:

for the drug chemically pure - 0.005 mg;

for the drug pure for analysis - 0.010 mg;

for the drug pure - 0.030 (0.050) mg.

The mass of iron indicated in brackets is established for the norm valid until 01/01/95.

At the same time, a control experiment is carried out under the same conditions and with the same amounts of reagents. If an iron impurity is detected, an amendment is made to the analysis result.

In case of disagreement in the assessment of the mass fraction of iron, the determination is carried out using the 2,2"-dipyridyl method.

3.10.1-3.10.2. (Introduced additionally, Amendment No. 1).

3.11. Determination of the mass fraction of arsenic is carried out according to GOST 10485-75 using the method using silver diethyldithiocarbamate or the method using bromine mercury paper.

(Changed edition, Amendment No. 1).

3.11.1. Silver diethyldithiocarbamate method

50 g (42.5 cm) of the drug is placed in a porcelain cup, 0.25 cm of concentrated nitric acid is added and evaporated in a water bath to a volume of 10 cm. After cooling, the residue is carefully transferred to a conical flask with a capacity of 100 cm, diluted with water and then determined using silver diethyldithiocarbamate.

The drug is considered to comply with the requirements of this standard if the mass of arsenic does not exceed:

for the drug chemically pure - 0.0025 mg;

for the drug pure for analysis - 0.0025 (0.0050) mg;

for the drug pure - 0.005 (0.010) mg.

3.11.2. Bromomercury paper method

20 g (17 cm) of the drug is placed in the flask of a device for determining arsenic, 6.5 cm of hydrochloric acid is added, the volume of the solution is adjusted to 150 cm with water, mixed and the determination is carried out using the arsine method in a volume of 150 cm (method 2), without adding a sulfuric solution acids.

The drug is considered to comply with the requirements of this standard if the color of brominated mercury paper from the analyzed solution is not more intense than the color of brominated mercury paper from the reference solution prepared simultaneously with the analyzed solution and containing 41.5 cm of solution;

for the drug chemically pure - 0.001 mg As;

for the drug pure for analysis - 0.001 (0.002) mg As;

for the drug pure - 0.002 (0.004) mg As,

6.5 cm of hydrochloric acid, 0.5 cm of stannous chloride solution and 5 g of zinc.

The mass of arsenic indicated in brackets is established for standards in force before 01/01/95.

In case of disagreement in the assessment of the mass fraction of arsenic, the determination is carried out using silver diethyldithiocarbamate

3.11.1-3.11.2. (Introduced additionally, Amendment No. 1).

3.12. Determination of the mass fraction of heavy metals

The determination is carried out according to GOST 17319-76. In this case, 10 g (8.5 cm) of the drug is placed in a porcelain cup and evaporated to dryness in a water bath. The dry residue is cooled, dissolved in 0.5 cm of hydrochloric acid solution, the contents of a 10 cm cup of water are washed off into a 50 cm flask, neutralized with a 25% ammonia solution to a slightly alkaline reaction, the volume of the solution is adjusted to 20 cm with water and the determination is carried out using the thioacetamide method. , photometrically or visually.

The drug is considered to comply with the requirements of this standard if the mass of heavy metals does not exceed:

for the drug chemically pure - 0.005 (0.01) mg;

for the drug pure for analysis - 0.01 mg;

for the drug pure - 0.02 mg.

The mass of heavy metals indicated in brackets is established for the norm valid until 01/01/95.

Determination using the hydrogen sulfide method is allowed.

In case of disagreement in the assessment of the mass fraction of heavy metals, the determination is carried out photometrically, using the thioacetamide method; in this case, the mass of a sample of the chemically pure preparation is and ch.d.a. should be 30 g (25.5 cm).

(Changed edition, Amendment No. 1).

4. PACKAGING, LABELING, TRANSPORTATION AND STORAGE

4.1. The drug is packaged and labeled in accordance with GOST 3885-73.

Type and type of container: 3-1, 3-2, 3-5, 3-8, 8-1, 8-2, 8-5, 9-1, 10-1.

Packing group: V, VI, VII.

Danger signs are applied to the container in accordance with GOST 19433-88 (class 8, subclass 8.1, drawing 8, classification code 8172) serial number UN 1789.

(Changed edition, Amendment No. 1).

4.2. The drug is transported by all modes of transport in accordance with the rules for the carriage of goods in force for this type of transport.

4.3. The drug is stored in the manufacturer's packaging in covered warehouses.

5. MANUFACTURER WARRANTY

5.1. The manufacturer guarantees that hydrochloric acid meets the requirements of this standard subject to storage and transportation conditions.

5.2. The guaranteed shelf life of the drug is one year from the date of manufacture.

Section 5. (Changed edition, Amendment No. 1).

Section 6. (Deleted, Amendment No. 1).



The text of the document is verified according to:
official publication
M.: IPK Standards Publishing House, 1997

Hydrochloric acid - inorganic substance, a monoprotic acid, one of the most strong acids. Other names are also used: hydrogen chloride, hydrochloric acid, hydrochloric acid.

Properties

Acid in its pure form is a colorless and odorless liquid. Industrial acid usually contains impurities that give it a slightly yellowish tint. Hydrochloric acid is often called “fuming” because it emits hydrogen chloride vapors, which react with moisture in the air and form acid fog.

Very soluble in water. At room temperature The maximum possible hydrogen chloride content by weight is 38%. An acid concentration greater than 24% is considered concentrated.

Hydrochloric acid actively reacts with metals, oxides, hydroxides, forming salts - chlorides. HCl reacts with salts of weaker acids; with strong oxidizing agents and ammonia.

To determine hydrochloric acid or chlorides, a reaction with silver nitrate AgNO3 is used, which results in the formation of a white cheesy precipitate.

Safety precautions

The substance is very caustic, corrodes skin, organic materials, metals and their oxides. When exposed to air, it releases hydrogen chloride vapors, which cause suffocation, burns to the skin, mucous membranes of the eyes and nose, damage the respiratory system, and destroy teeth. Hydrochloric acid belongs to substances of the 2nd degree of danger (highly dangerous), the maximum permissible concentration of the reagent in the air is 0.005 mg/l. You can work with hydrogen chloride only in filter gas masks and protective clothing, including rubber gloves, an apron, and safety shoes.

When acid spills, wash it off with plenty of water or neutralize it with alkaline solutions. Those affected by acid should be taken out of the danger area, rinse their skin and eyes with water or soda solution, and call a doctor.

The chemical reagent can be transported and stored in glass, plastic containers, as well as in metal containers coated on the inside with a rubber layer. The container must be hermetically sealed.

Receipt

On an industrial scale, hydrochloric acid is produced from hydrogen chloride (HCl) gas. Hydrogen chloride itself is produced in two main ways:
- exothermic reaction of chlorine and hydrogen - thus obtaining a high-purity reagent, for example, for the food industry and pharmaceuticals;
- from related industrial gases— an acid based on such HCl is called abgasic.

This is interesting

It was hydrochloric acid that nature “entrusted” with the process of breaking down food in the body. The concentration of acid in the stomach is only 0.4%, but this is enough to digest a razor blade in a week!

Acid is produced by the cells of the stomach itself, which is protected from this aggressive substance by the mucous membrane. However, its surface is renewed daily to restore damaged areas. In addition to participating in the process of digesting food, acid also performs a protective function, killing pathogens that enter the body through the stomach.

Application

- In medicine and pharmaceuticals - to restore the acidity of gastric juice in case of insufficiency; for anemia to improve the absorption of iron-containing drugs.
— In the food industry it is a food additive, acidity regulator E507, and also an ingredient in seltzer (soda) water. Used in the production of fructose, gelatin, citric acid.
- In the chemical industry - the basis for the production of chlorine, soda, monosodium glutamate, metal chlorides, for example zinc chloride, manganese chloride, ferric chloride; synthesis of organochlorine substances; catalyst in organic syntheses.
— Most of the hydrochloric acid produced in the world is consumed in metallurgy for cleaning workpieces from oxides. For these purposes, an inhibited industrial acid is used, which contains special reaction inhibitors (moderators), due to which the reagent dissolves oxides, but not the metal itself. Metals are also etched with hydrochloric acid; clean them before tinning, soldering, galvanizing.
— Treat the leather before tanning.
— In the mining industry it is in demand for cleaning boreholes from sediments, for processing ores and rock formations.
— In laboratory practice, hydrochloric acid is used as a popular reagent for analytical research and for cleaning vessels from difficult-to-remove contaminants.
— Used in the rubber, pulp and paper industries, and in ferrous metallurgy; for cleaning boilers, pipes, equipment from complex deposits, scale, rust; for cleaning ceramic and metal products.

Hydrochloric acid is a solution of hydrogen chloride in water. Hydrogen chloride (HCl) under normal conditions is a colorless gas with a specific pungent odor. However, we are dealing with its aqueous solutions, so we will focus only on them.

Hydrochloric acid is a colorless transparent solution with a pungent odor of hydrogen chloride. In the presence of impurities of iron, chlorine or other substances, the acid has a yellowish-green color. The density of a hydrochloric acid solution depends on the concentration of hydrogen chloride in it; some data is given in table 6.9.

Table 6.9. Density of hydrochloric acid solutions of various concentrations at 20°C.

From this table it can be seen that the dependence of the density of a hydrochloric acid solution on its concentration can be described with an accuracy satisfactory for technical calculations by the formula:

d = 1 + 0.5*(%) / 100

When dilute solutions boil, the HCl content in vapor is less than in solution, and when concentrated solutions boil, it is greater than in solution, which is reflected in the figure below. rice. 6.12 equilibrium diagram. Constantly boiling mixture (azeotrope) at atmospheric pressure has a composition of 20.22% wt. HCl, boiling point 108.6°C.

Finally, another important advantage of hydrochloric acid is the almost complete independence of the time of its acquisition from the time of year. As can be seen from rice. No. 6.13, acid of industrial concentration (32-36%) freezes at temperatures that are practically unattainable for the European part of Russia (from -35 to -45 ° C), unlike sulfuric acid, which freezes at positive temperatures, which requires the introduction of a tank heating operation.

Hydrochloric acid does not have the disadvantages of sulfuric acid.

Firstly, ferric chloride has increased solubility in hydrochloric acid solution (Fig. 6.14), which allows you to increase the concentration of ferric chloride in the solution to 140 g/l and even more; the danger of sediment formation on the surface disappears.

Working with hydrochloric acid can be carried out at any temperature inside the building (even at 10°C), and this does not cause noticeable changes in the composition of the solution.

Rice. 6.12. Liquid – vapor equilibrium diagram for the HCl – H 2 O system.

Rice. 6.13. State diagram (fusibility) of the HCl–H 2 O system.

Rice. 6.14. Equilibrium in the HCl – FeCl 2 system.

Finally, another very important advantage of hydrochloric acid is full compatibility with a flux that uses chlorides.

Some disadvantage of hydrochloric acid as a reagent is its high volatility. The standards allow a concentration of 5 mg/m 3 of air volume in the workshop. The dependence of vapor pressure in an equilibrium state over an acid of various percentage concentrations is given in table 6.10. In general, when the acid concentration in the bath is less than 15% by weight, this condition is satisfied. However, as temperatures in the workshop increase (i.e. summer time) this indicator may be exceeded. Certain information about what acid concentration is permissible at a specific workshop temperature can be determined from rice. 6.15.

The dependence of the etching rate on concentration and temperature is shown in rice. 6.16.

Etching defects are usually caused by the following:

• using an acid with a higher or lower concentration compared to the optimal one;
• short etching duration (the expected etching duration at different acid and iron concentrations can be estimated from rice. 6.17;
• reduced temperature compared to optimal;
• lack of mixing;
• laminar movement of the etching solution.

These problems are usually solved using specific technological techniques.

Table 6.10. Dependence of the equilibrium concentration of hydrogen chloride on the acid concentration in the bath.

Hydrochloric acid (hydrochloric acid) - an aqueous solution of hydrogen chloride HCl, is a clear, colorless liquid with a pungent odor of hydrogen chloride. Technical acid has a yellowish-green color due to impurities of chlorine and iron salts. The maximum concentration of hydrochloric acid is about 36% HCl; such a solution has a density of 1.18 g/cm3. Concentrated acid “smoke” in air, since the released gaseous HCl forms tiny droplets of hydrochloric acid with water vapor.

Hydrochloric acid is not flammable or explosive. It is one of the strongest acids; it dissolves (with the release of hydrogen and the formation of salts - chlorides) all metals in the voltage series up to hydrogen. Chlorides are also formed when hydrochloric acid reacts with metal oxides and hydroxides. It behaves as a reducing agent with strong oxidizing agents.

Salts of hydrochloric acid - chlorides, with the exception of AgCl, Hg2Cl2, are highly soluble in water. Glass, ceramics, porcelain, graphite, and fluoroplastic are resistant to it.

Hydrochloric acid is obtained by dissolving hydrogen chloride in water, which is synthesized either directly from hydrogen and chlorine or obtained by the action of sulfuric acid on sodium chloride.

The produced technical hydrochloric acid has a strength of at least 31% HCl (synthetic) and 27.5% HCl (from NaCI). A commercial acid is called concentrated if it contains 24% or more HCl; if the HCl content is less, then the acid is called dilute.

Hydrochloric acid is used to produce chlorides of various metals, organic intermediates and synthetic dyes, acetic acid, activated carbon, various adhesives, hydrolytic alcohol, and in electroplating. It is used for etching metals, for cleaning various vessels, casing pipes of boreholes from carbonates, oxides and other sediments and contaminants. In metallurgy, ores are treated with acid; in the leather industry, leather is treated with acid before tanning and dyeing. Hydrochloric acid is used in the textile, food industries, medicine, etc.

Hydrochloric acid plays an important role in the digestive process; it is an integral part of gastric juice. Diluted hydrochloric acid is prescribed orally mainly for diseases associated with insufficient acidity of gastric juice.

Hydrochloric acid is transported in glass bottles or rubberized (rubber-coated) metal vessels, as well as in plastic containers.

Hydrochloric acid very dangerous to human health. Causes severe burns upon contact with skin. Contact with eyes is especially dangerous.

If hydrochloric acid gets on the skin, it must be washed off immediately with plenty of water.

Fog and hydrogen chloride vapors formed when concentrated acid interacts with air are very dangerous. They irritate the mucous membranes and respiratory tract. Prolonged work in an HCl atmosphere causes catarrh of the respiratory tract, tooth decay, clouding of the cornea of ​​the eyes, ulceration of the nasal mucosa, gastrointestinal disorders.
Acute poisoning is accompanied by hoarseness, suffocation, runny nose, and cough.

In the event of a leak or spill, hydrochloric acid can cause significant damage environment . Firstly, this leads to the release of vapors of the substance into the atmospheric air in quantities exceeding sanitary and hygienic standards, which can lead to poisoning of all living things, as well as the appearance of acid precipitation, which can lead to changes in chemical properties soil and water.

Secondly, it can leak into groundwater, resulting in contamination. inland waters.
Where the water in rivers and lakes has become quite acidic (pH less than 5), fish disappear. When trophic chains are disrupted, the number of species of aquatic animals, algae and bacteria decreases.

In cities, acid precipitation accelerates the destruction of marble and concrete structures, monuments and sculptures. When it comes into contact with metals, hydrochloric acid causes corrosion, and when it reacts with substances such as bleach, manganese dioxide, or potassium permanganate, it forms toxic chlorine gas.

In the event of a spill, wash hydrochloric acid off surfaces with plenty of water or an alkaline solution that neutralizes the acid.

The material was prepared based on information from open sources