How to mix hydrochloric acid with water. acid solutions. Indications for use

Receipt. Hydrochloric acid is produced by dissolving hydrogen chloride in water.

Pay attention to the device shown in the figure on the left. It is used to produce hydrochloric acid. During the process of obtaining hydrochloric acid, monitor the gas outlet tube, it should be near the water level, and not be immersed in it. If this is not followed, then due to the high solubility of hydrogen chloride, water will enter the test tube with sulfuric acid and an explosion may occur.

In industry, hydrochloric acid is usually produced by burning hydrogen in chlorine and dissolving the reaction product in water.

physical properties. By dissolving hydrogen chloride in water, even a 40% hydrochloric acid solution with a density of 1.19 g/cm 3 can be obtained. However, commercially available concentrated hydrochloric acid contains about 0.37 mass fractions, or about 37% hydrogen chloride. The density of this solution is approximately 1.19 g/cm 3 . When an acid is diluted, the density of its solution decreases.

Concentrated hydrochloric acid is an invaluable solution, highly fuming in moist air, with a pungent odor due to the release of hydrogen chloride.

Chemical properties. Hydrochloric acid has a number of common properties that are characteristic of most acids. In addition, it has some specific properties.

Properties of HCL in common with other acids: 1) Color change of indicators 2) interaction with metals 2HCL + Zn → ZnCL 2 + H 2 3) Interaction with basic and amphoteric oxides: 2HCL + CaO → CaCl 2 + H 2 O; 2HCL + ZnO → ZnHCL 2 + H 2 O 4) Interaction with bases: 2HCL + Cu (OH) 2 → CuCl 2 + 2H 2 O 5) Interaction with salts: 2HCL + CaCO 3 → H 2 O + CO 2 + CaCL 2

Specific properties of HCL: 1) Interaction with silver nitrate (silver nitrate is a reagent for hydrochloric acid and its salts); precipitate will fall white color, which does not dissolve in water or acids: HCL + AgNO3 → AgCL ↓ + HNO 3 2

Application. A huge amount of hydrochloric acid is consumed to remove iron oxides before coating products from this metal with other metals (tin, chromium, nickel). In order for hydrochloric acid to react only with oxides, but not with metal, special substances called inhibitors are added to it. Inhibitors- Substances that slow down reactions.

Hydrochloric acid is used to obtain various chlorides. It is used to produce chlorine. Very often, a solution of hydrochloric acid is prescribed to patients with low acidity of gastric juice. Hydrochloric acid is found in everyone in the body, it is part of the gastric juice, which is necessary for digestion.

IN Food Industry hydrochloric acid is used only in the form of a solution. It is used to control acidity in the production citric acid, gelatin or fructose (E 507).

Do not forget that hydrochloric acid is dangerous for the skin. It poses an even greater danger to the eyes. Influencing a person, it can cause tooth decay, irritation of mucous membranes, and suffocation.

In addition, hydrochloric acid is actively used in electroplating and hydrometallurgy (scale removal, rust removal, leather treatment, chemical reagents, as a rock solvent in oil production, in the production of rubbers, sodium glutamate, soda, Cl 2). Hydrochloric acid is used for the regeneration of Cl 2 in organic synthesis (to obtain vinyl chloride, alkyl chlorides, etc.) It can be used as a catalyst in the production of diphenylolpropane, benzene alkylation.

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

Properties of a chemical compound

HCl is used in various fields of human activity. It dissolves metals and their oxides, is absorbed in benzene, ether and water, does not destroy fluoroplastic, glass, ceramics and graphite. Its safe use is possible when storing and working in right conditions with all safety precautions.

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

Scope of application of an aqueous solution of hydrogen chloride

The use 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 cleaning;
• in galvanoplasty - during etching and pickling;
• in the production of soda water for acidity control, in the manufacture alcoholic beverages and syrups in the food industry;
• for leather processing in light industry;
• when treating non-potable 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 a hydrochloric acid solution is the alignment of the acid-base balance in the human body. A weak solution, or drugs, is treated low acidity stomach. This optimizes the digestion of food, helps fight germs and bacteria that enter from the outside. Chemically pure hydrochloric acid helps to normalize the low level of gastric acidity and optimizes the digestion of proteins.

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

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

Hydrochloric acid is a solution of hydrogen chloride in water. Hydrogen chloride (HCl) at normal conditions 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 with an accuracy satisfactory for technical calculations can be described by the formula:

d = 1 + 0.5*(%) / 100

When dilute solutions boil, the HCl content in vapors is less than in solution, and when concentrated solutions boil, it is higher than in solution, which is reflected in the figure. rice. 6.12 equilibrium diagram. A 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 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.

First, ferric chloride has an increased solubility in hydrochloric acid solution. (Fig. 6.14), which allows you to raise the concentration of ferric chloride in the solution to a value of 140 g/l and even more; the risk of sediment formation on the surface disappears.

Work 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. Equilibrium diagram liquid - vapor for the system HCl - H 2 O.

Rice. 6.13. Diagram of the state (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 its full compatibility with flux, which uses chlorides.

Some disadvantage of hydrochloric acid as a reagent is its high volatility. The standards allow the concentration of 5 mg / m 3 of air volume in the workshop. The dependence of vapor pressure in the equilibrium state over acid of various percentage concentrations is given in table 6.10. In general, when the acid concentration in the bath is less than 15 wt %, this condition is satisfied. However, when temperatures rise in the workshop (that is, in summer time) it is possible to exceed this indicator. Certain information about what acid concentration at a particular shop temperature is acceptable can be determined from rice. 6.15.

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

Pickling deficiencies are usually caused by the following:

• using an acid with a greater or lesser concentration, compared to the optimal;
• short etching duration (the expected etching duration at different concentrations of acid and iron can be estimated from rice. 6.17;
• lower temperature compared to the optimum;
• lack of mixing;
• laminar motion of the pickling solution.

These problems are usually solved with the help of specific technological methods.

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

Hydrochloric acid - inorganic matter, a monobasic acid, one of the strongest acids. Other names are also used: hydrogen chloride, hydrochloric acid, hydrochloric acid.

Properties

Acid in its pure form is a colorless and odorless liquid. Technical acid usually contains impurities that give it a slightly yellowish tint. Hydrochloric acid is often referred to as "fuming" because it releases hydrogen chloride vapor, which reacts with atmospheric moisture to form an acid mist.

It dissolves very well in water. At room temperature, the maximum possible mass content of hydrogen chloride is -38%. An acid concentration greater than 24% is considered concentrated.

Hydrochloric acid actively reacts with metals, oxides, hydroxides, forming salts - chlorides. HCl interacts 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, as a result of which a white cheesy precipitate precipitates.

Safety

The substance is very caustic, corrosive to skin, organic materials, metals and their oxides. In the air, it emits 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 the substances of the 2nd degree of danger (highly dangerous), the MPC of the reagent in the air is 0.005 mg/l. It is possible to work with hydrogen chloride only in filter gas masks and protective clothing, including rubber gloves, an apron, safety shoes.

If acid is spilled, it is washed off with large amounts of water or neutralized with alkaline solutions. Victims of acid should be taken out of the danger zone, rinse the skin and eyes with water or soda solution, call a doctor.

It is allowed to transport and store a chemical reagent in a glass, plastic container, as well as in a metal container, covered from the inside with a rubber layer. The container must be hermetically sealed.

Receipt

Commercially, hydrochloric acid is produced from hydrogen chloride (HCl) gas. Hydrogen chloride itself is produced in two main ways:
- exothermic reaction of chlorine and hydrogen - in this way a high purity reagent is obtained, for example, for the food industry and pharmaceuticals;
- from accompanying industrial gases - an acid based on such HCl is called off-gas.

It's curious

It is to hydrochloric acid that nature "entrusted" the process of splitting 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!

The 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 updated daily to repair damaged areas. In addition to participating in the process of digestion of 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 its insufficiency; with anemia to improve the absorption of iron-containing drugs.
- In the food industry food supplement, acidity regulator E507, as well as an ingredient in seltzer (soda) water. Used in the manufacture of fructose, gelatin, citric acid.
- IN chemical industry- the basis for the production of chlorine, soda, sodium glutamate, metal chlorides, for example zinc chloride, manganese chloride, iron chloride; synthesis of organochlorine substances; catalyst in organic synthesis.
- Most of the hydrochloric acid produced in the world is used in metallurgy to clean workpieces from oxides. For these purposes, an inhibited technical acid is used, which contains special inhibitors (retarders) of the reaction, due to which the reagent dissolves oxides, but not the metal itself. Metals are also poisoned with hydrochloric acid; clean them before tinning, soldering, galvanizing.
- Process the skin before tanning.
- In the mining industry, it is in demand for cleaning boreholes from deposits, for processing ores and rock formations.
- In laboratory practice, hydrochloric acid is used as a popular reagent for analytical studies, for cleaning vessels from hard-to-remove contaminants.
- It is used in the rubber, pulp and paper industry, in ferrous metallurgy; for cleaning boilers, pipes, equipment from complex deposits, scale, rust; for cleaning ceramic and metal products.

approximate solutions. In most cases, the laboratory has to use hydrochloric, sulfuric and nitric acids. Acids are commercially available in the form of concentrated solutions, the percentage of which is determined by their density.

The acids used in the laboratory are technical and pure. Technical acids contain impurities, and therefore are not used in analytical work.

Concentrated hydrochloric acid smokes in air, so you need to work with it in a fume hood. The most concentrated hydrochloric acid has a density of 1.2 g/cm3 and contains 39.11% hydrogen chloride.

Dilution of the acid is carried out according to the calculation described above.

Example. It is necessary to prepare 1 liter of a 5% solution of hydrochloric acid, using its solution with a density of 1.19 g / cm3. According to the reference book, we learn that a 5% solution has a density of 1.024 g / cm3; therefore, 1 liter of it will weigh 1.024 * 1000 \u003d 1024 g. This amount should contain pure hydrogen chloride:

Acid with a density of 1.19 g/cm3 contains 37.23% HCl (we also find it in the reference book). To find out how much this acid should be taken, make up the proportion:

or 137.5 / 1.19 \u003d 115.5 acids with a density of 1.19 g / cm3. Having measured 116 ml of an acid solution, bring its volume to 1 liter.

Sulfuric acid is also diluted. When diluting it, remember that you need to add acid to water ~, and not vice versa. When diluted, strong heating occurs, and if water is added to the acid, it may splash, which is dangerous, since sulfuric acid causes severe burns. If acid gets on clothes or shoes, quickly wash the spilled area with plenty of water, and then neutralize the acid with sodium carbonate or ammonia solution. In case of contact with the skin of the hands or face, immediately wash the area with plenty of water.

Special care must be taken when handling oleum, which is sulfuric acid monohydrate saturated with sulfuric anhydride SO3. According to the content of the latter, oleum comes in several concentrations.

It should be remembered that with a slight cooling, the oleum crystallizes and is in a liquid state only at room temperature. In air, it smokes with the release of SO3, which forms sulfuric acid vapors when interacting with air moisture.

Great difficulties are caused by the transfusion of oleum from a large container into a small one. This operation should be carried out either under draft or in air, but where the resulting sulfuric acid and SO3 cannot have any harmful effect on people and surrounding objects.

If the oleum has hardened, it should first be heated by placing the container with it in a warm room. When the oleum melts and turns into an oily liquid, it must be taken out into the air and poured into smaller dishes, using the method of squeezing with the help of air (dry) or an inert gas (nitrogen).

When mixed with water, nitric acid also heats up (although not as strong as in the case of sulfuric acid), and therefore precautions must be taken when working with it.

In laboratory practice, solid organic acids are used. Handling them is much easier and more convenient than liquid ones. In this case, care should only be taken to ensure that the acids are not contaminated by anything foreign. If necessary, solid organic acids are purified by recrystallization (see Ch. 15 "Crystallization"),

precise solutions. Accurate acid solutions they are prepared in the same way as the approximate ones, with the only difference that at first they strive to obtain a solution of a slightly higher concentration, so that after that it can be diluted accurately, according to calculation. For precise solutions, only chemically pure preparations are taken.

The required amount of concentrated acids is usually taken by volume, calculated from the density.

Example. It is necessary to prepare 0.1 and. H2SO4 solution. This means that 1 liter of solution should contain:

Acid with a density of 1.84 g / cmg contains 95.6% H2SO4 n for the preparation of 1 l of 0.1 n. solution, you need to take the following amount (x) of it (in g):

The corresponding volume of acid will be:

Having measured exactly 2.8 ml of acid from a burette, dilute it to 1 liter in a volumetric flask and then titrate with an alkali solution and establish the normality of the resulting solution. If the solution turns out to be more concentrated), the calculated amount of water is added to it from the burette. For example, during titration, it was found that 1 ml of 6.1 N. H2SO4 solution contains not 0.0049 g H2SO4, but 0.0051 g. To calculate the amount of water that is needed to prepare exactly 0.1 N. solution, make up the proportion:

The calculation shows that this volume is equal to 1041 ml. the solution must be added 1041 - 1000 = 41 ml of water. It should also take into account the amount of solution that is taken for titration. Let 20 ml be taken, which is 20/1000 = 0.02 of the available volume. Therefore, water should be added not 41 ml, but less: 41 - (41 * 0.02) \u003d \u003d 41 -0.8 \u003d 40.2 ml.

* To measure acid, use a carefully dried burette with a ground stopcock. .

The corrected solution should be checked again for the content of the substance taken for dissolution. Accurate solutions of hydrochloric acid are also prepared by the ion-exchange method, based on the exact calculated sample of sodium chloride. The sample calculated and weighed on an analytical balance is dissolved in distilled or demineralized water, the resulting solution is passed through a chromatographic column filled with a cation exchanger in the H-form. The solution flowing from the column will contain an equivalent amount of HCl.

As a rule, exact (or titrated) solutions should be stored in tightly closed flasks. It is imperative to insert a calcium chloride tube into the cork of the vessel, filled in the case of an alkali solution with soda lime or ascarite, and in the case of an acid, with calcium chloride or simply cotton wool.

To check the normality of acids, calcined sodium carbonate Na2COs is often used. However, it is hygroscopic and therefore does not fully meet the requirements of analysts. It is much more convenient to use for these purposes acidic potassium carbonate KHCO3, dried in a desiccator over CaCl2.

When titrating, it is useful to use a “witness”, for the preparation of which one drop of acid (if titrating alkali) or alkali (if titrating acid) and as many drops of an indicator solution as added to the titrated solution are added to distilled or demineralized water.

The preparation of empirical, according to the substance being determined, and standard solutions, acids is carried out according to the calculation using the formulas given for these and the cases described above.