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 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, with an increase in temperatures in the workshop (that is, in the summer), this indicator may be exceeded. 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.

Acid concentration, %		Acid concentration, %	The concentration of HCl in the air, mg / m 3
	4500 (20°C)

Hydrochloric acid tank

One of the strong monobasic acids and is formed when a gas is dissolved hydrogen chloride(HCl) in water, is a clear, colorless liquid with a characteristic odor of chlorine. dilute hydrochloric acid(as well as phosphoric) is often used to remove oxides when soldering metals.

Sometimes the gaseous compound HCl is erroneously called hydrochloric acid. HCl is a gas that, when dissolved in water, forms hydrochloric acid.

Hydrogen chloride It is a colorless gas with a pungent, suffocating odor of chlorine. It goes into a liquid state at -84 0 C, and at -112 0 C it goes into a solid state.

Hydrogen chloride very soluble in water. So at 0 0 C, 500 liters of hydrogen chloride dissolve in 1 liter of water.
In the dry state, hydrogen chloride gas is quite inert, but it can already interact with some organic substances, such as acetylene (the gas that is released when carbide is lowered into water).

Chemical properties of hydrochloric acid

Chemical reaction with metals:
2HCl + Zn \u003d ZnCl 2 + H 2 - a salt is formed (in this case, a clear solution of zinc chloride) and hydrogen
- chemical reaction with metal oxides:
2HCl + CuO \u003d CuCl 2 + H 2 O - a salt is formed (in this case, a green copper chloride salt solution) and water
- chemical reaction with bases and alkalis (or neutralization reaction)
HCl + NaOH \u003d NaCl + H 2 O - neutralization reaction, - a salt is formed (in this case, a clear solution of sodium chloride) and water.
- chemical reaction with salts (for example, with CaCO 3 chalk):
HCl + СaCO 3 \u003d CaCl 2 + CO 2 + H 2 O - carbon dioxide, water and a clear solution of calcium chloride CaCl 2 are formed.

Getting hydrochloric acid

hydrochloric acid obtained by a chemical reaction of the compound:

H 2 + Cl 2 \u003d HCl - the reaction occurs at an elevated temperature

And also in the interaction of table salt and concentrated sulfuric acid:

H 2 SO 4 (conc.) + NaCl \u003d NaHSO 4 + HCl

In this reaction, if NaCl is a solid, then HCl is a gas hydrogen chloride which, when dissolved in water, forms hydrochloric acid

There are complex chemicals that are similar in chemical structure to hydrochloric acid, but at the same time contain from one to four oxygen atoms in the molecule. These substances can be called oxygenated acids. With an increase in the number of oxygen atoms, the stability of the acid and its oxidizing ability increase.

To oxygenated acids following:

• hypochlorous (HClO),
• chloride (HClO 2),
• chloric (HClO 3),
• chloride (HClO 4).

Each of these chemical complex substances has all properties of acids and is capable of forming salts. Hypochlorous acid(HClO) forms hypochlorites, for example, the compound NaClO is sodium hypochlorite. Hypochlorous acid itself is formed when chlorine is dissolved in cold water by a chemical reaction:

H 2 O + Cl 2 \u003d HCl + HClO,

As you can see, in this reaction two acids are formed at once - hydrochloric HCl and hypochlorous HClO. But the latter is an unstable chemical compound and gradually turns into hydrochloric acid;

Chloride HClO 2 forms chlorites, salt NaClO 2 - sodium chlorite;
chlorine(HClO 3) - chlorates, KClO 3 compound, - potassium chlorate (or Berthollet salt) - by the way, this substance is widely used in the manufacture of matches.

And finally, the strongest of the known monobasic acids - chloride(HClO 4) - colorless, fuming in air, highly hygroscopic liquid, - forms perchlorates, for example, KClO 4 - potassium perchlorate.

Salts formed hypochlorous HClO and chloride HClO 2 acids are not stable in the free state and are strong oxidizing agents in aqueous solutions. But the salts formed chlorine HClO 3 and chloride HClO 4 acids based on alkali metals (for example, Bertolet's salt KClO 3) are quite stable and do not exhibit oxidizing properties.

Description of the substance

Hydrochloric acid is an aqueous solution of hydrogen chloride. The chemical formula of this substance is HCl. In water, the mass of hydrogen chloride at the highest concentration cannot exceed 38%. At room temperature, hydrogen chloride is in a gaseous state. To pass it into a liquid state, it must be cooled to minus 84 degrees Celsius, in solid - to minus 112 degrees. The density of concentrated acid at room temperature is 1.19 g/cm 3 . This liquid is part of the gastric juice, which ensures the digestion of food. In this state, its concentration does not exceed 0.3%.

Properties of hydrochloric acid

A solution of hydrogen chloride is chemically harmful, its hazard class is the second.

Hydrochloric liquid is a strong monobasic acid that can react with many metals, their salts, oxides and hydroxides, it can react with silver nitrate, ammonia, calcium hypochlorite and strong oxidizing agents:

Physical properties and effects on the body

At high concentrations, it is a caustic substance that can cause burns not only to the mucous membranes, but also to the skin. You can neutralize it with a solution of baking soda. When containers with a concentrated brine solution are opened, its vapors, in contact with moisture in the air, form a condensate of toxic vapors in the form of tiny droplets (aerosol), which irritates the respiratory tract and eyes.

The concentrated substance has a characteristic pungent odor. Technical grades of hydrogen chloride solution are divided into:

red unrefined, its color is mainly due to impurities of ferric chloride;

purified, colorless liquid, in which the concentration of HCl is about 25%;

fuming, concentrated, liquid with HCl concentration of 35-38%.

Chemical properties

How to receive

The process of production of saline liquid consists of the stages of obtaining hydrogen chloride and absorption (absorption) of it with water.

Exist three industrial ways production of hydrogen chloride:

synthetic

sulfate

from side gases (off-gases) of a number of technological processes. The last method is the most common. By-product HCl is usually formed during the dehychlorination and chlorination of organic compounds, the manufacture of potash fertilizers, the pyrolysis of metal chlorides or organic waste containing chlorine.

Storage and transportation

Industrial hydrochloric acid is stored and transported in specialized polymer-coated tanks and containers, polyethylene barrels, glass bottles packed in boxes. Hatches of containers and tanks, corks of barrels and bottles must ensure the tightness of the container. The acid solution should not come into contact with metals that are in the voltage line to the left of hydrogen, as this can cause explosive mixtures.

Application

in metallurgy for the extraction of ores, removal of rust, scale, dirt and oxides, soldering and tinning;

in the manufacture of synthetic rubbers and resins;

in electroplating;

as an acidity regulator in the food industry;

to obtain metal chlorides;

to obtain chlorine;

in medicine for the treatment of insufficient acidity of gastric juice;

as a cleaner and disinfectant.

Structural formula

True, empirical, or gross formula: HCl

Chemical composition of hydrochloric acid

Molecular weight: 36.461

Hydrochloric acid(also hydrochloric, hydrochloric acid, hydrogen chloride) - a solution of hydrogen chloride (HCl) in water, a strong monobasic acid. Colorless, transparent, caustic liquid, "fuming" in air (technical hydrochloric acid is yellowish due to impurities of iron, chlorine, etc.). At a concentration of about 0.5%, it is present in the human stomach. The maximum concentration at 20 °C is 38% by weight, the density of such a solution is 1.19 g/cm³. Molar mass 36.46 g/mol. Salts of hydrochloric acid are called chlorides.

Physical properties

The physical properties of hydrochloric acid are highly dependent on the concentration of dissolved hydrogen chloride. When solidified, it gives crystalline hydrates of the compositions HCl H 2 O, HCl 2H 2 O, HCl 3H 2 O, HCl 6H 2 O.

Chemical properties

• Interaction with metals standing in a series of electrochemical potentials up to hydrogen, with the formation of a salt and the release of gaseous hydrogen.
• Interaction with metal oxides to form a soluble salt and water.
• Interaction with metal hydroxides to form a soluble salt and water (neutralization reaction).
• Interaction with metal salts formed by weaker acids, such as carbonic.
• Interaction with strong oxidizing agents (potassium permanganate, manganese dioxide) with the release of gaseous chlorine.
• Interaction with ammonia with the formation of thick white smoke, consisting of the smallest crystals of ammonium chloride.
• A qualitative reaction to hydrochloric acid and its salts is its interaction with silver nitrate, which forms a curd precipitate of silver chloride, insoluble in nitric acid.

Receipt

Hydrochloric acid is produced by dissolving hydrogen chloride gas in water. Hydrogen chloride is obtained by burning hydrogen in chlorine, the acid obtained in this way is called synthetic. Hydrochloric acid is also obtained from off-gases - by-product gases generated during various processes, for example, during the chlorination of hydrocarbons. The hydrogen chloride contained in these gases is called off-gas, and the acid thus obtained is called off-gas. In recent decades, the share of waste hydrochloric acid in the production volume has been gradually increasing, displacing the acid obtained by burning hydrogen in chlorine. But hydrochloric acid obtained by burning hydrogen in chlorine contains fewer impurities and is used when high purity is required. In laboratory conditions, a method developed by alchemists is used, which consists in the action of concentrated sulfuric acid on table salt. At temperatures above 550 °C and an excess of table salt, interaction is possible. It is possible to obtain by hydrolysis of chlorides of magnesium, aluminum (hydrated salt is heated). These reactions may not go to completion with the formation of basic chlorides (oxychlorides) of variable composition, for example. Hydrogen chloride is highly soluble in water. So, at 0 °C, 1 volume of water can absorb 507 volumes of HCl, which corresponds to an acid concentration of 45%. However, at room temperature, the solubility of HCl is lower, so 36% hydrochloric acid is usually used in practice.

Application

Industry

• It is used in hydrometallurgy and electroforming (etching, pickling), for cleaning the surface of metals during soldering and tinning, for obtaining chlorides of zinc, manganese, iron, and other metals. In a mixture with surfactants, it is used to clean ceramic and metal products (inhibited acid is needed here) from contamination and disinfection.
• It is registered in the food industry as an acidity regulator (food additive E507). It is used to make seltzer (soda) water.

The medicine

• A natural component of human gastric juice. At a concentration of 0.3-0.5%, usually mixed with the enzyme pepsin, it is administered orally with insufficient acidity.

Features of circulation

Highly concentrated hydrochloric acid is a corrosive substance that causes severe chemical burns if it comes into contact with the skin. Eye contact is especially dangerous. To neutralize burns, a weak alkali solution, usually baking soda, is used. When opening vessels with concentrated hydrochloric acid, hydrogen chloride vapor, attracting moisture from the air, forms a fog that irritates the eyes and respiratory tract of a person. Reacts with strong oxidizing agents (chlorine, manganese dioxide, potassium permanganate) to form toxic chlorine gas. In the Russian Federation, the circulation of hydrochloric acid with a concentration of 15% or more is limited.

What is hydrochloric acid solution? It is a compound of water (H2O) and hydrogen chloride (HCl), which is a colorless thermal gas with a characteristic odor. Chlorides are highly soluble and decompose into ions. Hydrochloric acid is the most well-known compound that forms HCl, so we can talk about it and its features in detail.

Description

Hydrochloric acid solution belongs to the class of strong. It is colorless, transparent and caustic. Although technical hydrochloric acid has a yellowish color due to the presence of impurities and other elements. It "smokes" in the air.

It is worth noting that this substance is also present in the body of every person. In the stomach, to be more precise, at a concentration of 0.5%. Interestingly, this amount is enough to completely destroy the razor blade. The substance will corrode it in just a week.

Unlike the same sulfuric acid, by the way, the mass of hydrochloric acid in solution does not exceed 38%. We can say that this indicator is a “critical” point. If you start to increase the concentration, then the substance will simply evaporate, as a result of which hydrogen chloride will simply evaporate with water. Plus, this concentration is maintained only at 20 ° C. The higher the temperature, the faster the evaporation.

Interaction with metals

Hydrochloric acid solution can enter into many reactions. First of all, with metals that stand before hydrogen in a series of electrochemical potentials. This is the sequence in which the elements go as their characteristic measure, the electrochemical potential (φ 0), increases. This indicator is extremely important in the cation reduction half-reactions. In addition, it is this series that demonstrates the activity of metals, which they exhibit in redox reactions.

So, interaction with them occurs with the release of hydrogen in the form of gas and with the formation of salt. Here is an example of a reaction with sodium, a soft alkali metal: 2Na + 2HCl → 2NaCl + H 2 .

With other substances, the interaction proceeds according to similar formulas. This is how the reaction with aluminum, a light metal, looks like: 2Al + 6HCl → 2AlCl 3 + 3H 2.

Reactions with oxides

Hydrochloric acid solution also interacts well with these substances. Oxides are binary compounds of an element with oxygen, having an oxidation state of -2. All known examples are sand, water, rust, dyes, carbon dioxide.

Hydrochloric acid does not interact with all compounds, but only with metal oxides. The reaction also produces a soluble salt and water. An example is the process that occurs between acid and magnesium oxide, an alkaline earth metal: MgO + 2HCl → MgCl 2 + H 2 O.

Reactions with hydroxides

This is the name of inorganic compounds in the compositions of which there is a hydroxyl group -OH, in which the hydrogen and oxygen atoms are connected by a covalent bond. And, since the hydrochloric acid solution only interacts with metal hydroxides, it is worth mentioning that some of them are called alkalis.

So the resulting reaction is called neutralization. Its result is the formation of a weakly dissociating substance (i.e. water) and salt.

An example is the reaction of a small volume of hydrochloric acid solution and barium hydroxide, a soft alkaline earth malleable metal: Ba(OH) 2 + 2HCl = BaCl 2 + 2H 2 O.

Interaction with other substances

In addition to the above, hydrochloric acid can also react with other types of compounds. In particular with:

• Metal salts, which are formed by other, weaker acids. Here is an example of one of these reactions: Na 2 Co 3 + 2HCl → 2NaCl + H 2 O + CO 2. Shown here is the interaction with a salt formed by carbonic acid (H 2 CO 3).
• Strong oxidizers. With manganese dioxide, for example. Or with potassium permanganate. These reactions are accompanied by the release of chlorine. Here is one example: 2KMnO 4 + 16HCl → 5Cl 2 + 2MnCl 2 + 2KCl + 8H 2 O.
• ammonia. It is hydrogen nitride with the formula NH 3 , which is a colorless but pungent gas. The consequence of its reaction with a solution of hydrochloric acid is a mass of thick white smoke, consisting of small crystals of ammonium chloride. Which, by the way, is known to everyone as ammonia (NH 4 Cl). The interaction formula is as follows: NH 3 + HCl → NH 4 CL.
• Silver nitrate - an inorganic compound (AgNO 3), which is a salt of nitric acid and silver metal. Due to the contact of a solution of hydrochloric acid with it, a qualitative reaction occurs - the formation of a cheesy precipitate of silver chloride. which does not dissolve in nitric acid. It looks like this: HCL + AgNO 3 → AgCl ↓ + HNO 3.

Getting a substance

Now we can talk about what they do to form hydrochloric acid.

First, by burning hydrogen in chlorine, the main component, gaseous hydrogen chloride, is obtained. which is then dissolved in water. The result of this simple reaction is the formation of a synthetic acid.

This substance can also be obtained from off-gases. These are chemical waste (side) gases. They are formed by a variety of processes. For example, when chlorinating hydrocarbons. The hydrogen chloride in their composition is called off-gas. And the acid thus obtained, respectively.

It should be noted that in recent years the share of the off-gas substance in the total volume of its production has been increasing. And the acid formed as a result of burning hydrogen in chlorine is displaced. However, in fairness, it should be noted that it contains fewer impurities.

Application in everyday life

Many cleaning products that householders use regularly contain a certain amount of hydrochloric acid solution. 2-3 percent, and sometimes less, but it's there. That is why, putting plumbing in order (washing tiles, for example), you need to wear gloves. Highly acid products can harm the skin.

Another solution is used as a stain remover. It helps to get rid of ink or rust on clothes. But in order for the effect to be noticeable, it is necessary to use a more concentrated substance. A 10% hydrochloric acid solution will do. He, by the way, perfectly removes scale.

It is important to store the substance correctly. Keep acid in glass containers and in places where animals and children cannot reach. Even a weak solution that gets on the skin or mucous membranes can cause a chemical burn. If this happens, immediately rinse the areas with water.

In the field of construction

The use of hydrochloric acid and its solutions is a popular way to improve many building processes. For example, it is often added to concrete mix to increase frost resistance. In addition, this way it hardens faster, and the resistance of the masonry to moisture increases.

Hydrochloric acid is also used as a limestone cleaner. Its 10% solution is the best way to deal with dirt and marks on red brick. It is not recommended to use it for cleaning others. The structure of other bricks is more sensitive to the action of this substance.

In medicine

In this area, the substance under consideration is also actively used. Dilute hydrochloric acid has the following effects:

• Digests proteins in the stomach.
• Stops the development of malignant tumors.
• Helps in the treatment of cancer.
• Normalizes acid-base balance.
• Serves as an effective tool in the prevention of hepatitis, diabetes, psoriasis, eczema, rheumatoid arthritis, cholelithiasis, rosacea, asthma, urticaria and many other ailments.

Did you come up with the idea to dilute the acid and use it inside in this form, and not as part of medicines? This is practiced, but it is strictly forbidden to do this without medical advice and instructions. Having calculated the proportions incorrectly, you can swallow an excess of hydrochloric acid solution, and simply burn your stomach.

By the way, you can still take medications that stimulate the production of this substance. And not just chemicals. The same calamus, peppermint and wormwood contribute to this. You can make decoctions based on them yourself, and drink them for prevention.

Burns and poisoning

As effective as this remedy is, it is dangerous. Hydrochloric acid, depending on the concentration, can cause chemical burns of four degrees:

1. There is only redness and pain.
2. There are blisters with a clear liquid and swelling.
3. Formed necrosis of the upper layers of the skin. Blisters fill with blood or cloudy contents.
4. The lesion reaches the tendons and muscles.

If the substance somehow got into the eyes, it is necessary to rinse them with water, and then with a soda solution. But in any case, the first thing to do is to call an ambulance.

The ingestion of acid inside is fraught with acute pains in the chest and abdomen, swelling of the larynx, vomiting bloody masses. As a result, severe pathologies of the liver and kidneys.

And the first signs of poisoning in pairs include a dry frequent cough, choking, damage to the teeth, burning in the mucous membranes and abdominal pain. The first emergency aid is washing and rinsing the mouth with water, as well as access to fresh air. Only a toxicologist can provide real help.