Hydrogen chloride is formed by reaction. Hydrogen chloride: formula, preparation, physical and chemical properties, safety precautions

Tank with hydrochloric acid

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

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

Hydrogen chloride- a colorless gas with a sharp suffocating odor of chlorine. It turns into a liquid state at -84 0 C, and at -112 0 C it turns 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 a dry state, hydrogen chloride gas is quite inert, but can already interact with some organic substances, for example with acetylene (a gas that is released when carbide is lowered into water).

Chemical properties of hydrochloric acid

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

Obtaining hydrochloric acid

Hydrochloric acid are obtained using a chemical reaction of the compound:

H 2 + Cl 2 = HCl - the reaction occurs at elevated temperatures

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

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

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

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

TO oxygen-containing acids the following:

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

Each of these chemical complexes 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 dissolves in cold water By chemical reaction:

H 2 O + Cl 2 = HCl + HClO,

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

Chloride HClO2 forms chlorites, salt NaClO 2 - sodium chlorite;
hypochlorous(HClO3) - chlorates, compound KClO 3, - potassium chlorate (or Berthollet's salt) - by the way, this substance is widely used in the manufacture of matches.

And finally, the strongest known monobasic acid - chlorine(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 unstable in the free state and are strong oxidizing agents in aqueous solutions. But the salts formed hypochlorous HClO 3 and chlorine HClO 4 with acids based on alkali metals (for example, Berthollet salt KClO 3) are quite stable and do not exhibit oxidizing properties.

Hydrogen chloride - what is it? Hydrogen chloride is a colorless gas with a pungent odor. It dissolves easily in water, forming hydrochloric acid. Chemical formula hydrogen chloride - HCl. It consists of a hydrogen and chlorine atom joined by a polar covalent bond. Hydrogen chloride easily dissociates in polar solvents, which provides good acidic properties of this compound. The bond length is 127.4 nm.

Physical properties

As stated above, in in good condition Hydrogen chloride is a gas. It is somewhat heavier than air, and also has hygroscopicity, that is, it attracts water vapor directly from the air, thereby forming a thick cloud of vapor. For this reason, hydrogen chloride is said to “smoke” in air. If this gas is cooled, at around -85 °C it liquefies, and at -114 °C it becomes a solid. At a temperature of 1500 °C it decomposes into simple substances (based on the formula of hydrogen chloride, into chlorine and hydrogen).

A solution of HCl in water is called hydrochloric acid. It is a colorless, caustic liquid. Sometimes it has a yellowish tint due to impurities of chlorine or iron. Due to hygroscopicity, the maximum concentration at 20 °C is 37-38% by weight. Others also depend on her. physical properties: density, viscosity, melting and boiling points.

Chemical properties

Hydrogen chloride itself usually does not react. Only when high temperature(more than 650 °C) it reacts with sulfides, carbides, nitrides and borides, as well as transition metal oxides. In the presence of Lewis acids, it can react with boron, silicon and germanium hydrides. But its aqueous solution is much more chemically active. According to its formula, hydrogen chloride is an acid, so it has some properties of acids:

• Interaction with metals (which are in the electrochemical voltage range up to hydrogen):

Fe + 2HCl = FeCl 2 + H 2

• Interaction with amphoteric and basic oxides:

BaO + 2HCl = BaCl 2 + H 2 O

• Interaction with alkalis:

NaOH + HCl = NaCl + H2O

Interaction with some salts:

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

• When reacting with ammonia, ammonium chloride salt is formed:

NH 3 + HCl = NH 4 Cl

But hydrochloric acid does not react with lead due to passivation. This is due to the formation of a layer of lead chloride on the surface of the metal, which is insoluble in water. Thus, this layer protects the metal from further interaction with hydrochloric acid.

In organic reactions, it can join through multiple bonds (hydrohalogenation reaction). It can also react with proteins or amines, forming organic salts - hydrochlorides. Man-made fibers, such as paper, are destroyed when interacting with hydrochloric acid. In redox reactions with strong oxidizing agents, hydrogen chloride is reduced to chlorine.

A mixture of concentrated hydrochloric and nitric acid (3 to 1 by volume) is called “aqua regia.” It is an extremely strong oxidizing agent. Due to the formation of free chlorine and nitrosyl in this mixture, aqua regia can even dissolve gold and platinum.

Receipt

Previously, in industry, hydrochloric acid was obtained by reacting sodium chloride with acids, usually sulfuric acid:

2NaCl + H 2 SO 4 = 2HCl + Na 2 SO 4

But this method is not effective enough, and the purity of the resulting product is low. Now another method is used to obtain (from simple substances) hydrogen chloride according to the formula:

H2 + Cl2 = 2HCl

To implement this method, there are special installations where both gases are supplied in a continuous flow to the flame in which the interaction occurs. Hydrogen is supplied in a slight excess so that all the chlorine reacts and does not contaminate the resulting product. Next, hydrogen chloride is dissolved in water to form hydrochloric acid.

In the laboratory, more diverse methods of preparation are possible, for example hydrolysis of phosphorus halides:

PCl 5 + H 2 O = POCl 3 + 2HCl

Hydrochloric acid can also be obtained by hydrolysis of crystalline hydrates of certain metal chlorides at elevated temperatures:

AlCl 3 6H 2 O = Al(OH) 3 + 3HCl + 3H 2 O

Hydrogen chloride is also a by-product of the chlorination reactions of many organic compounds.

Application

Hydrogen chloride itself is not used in practice, since it very quickly absorbs water from the air. Almost all of the hydrogen chloride produced goes into the production of hydrochloric acid.

It is used in metallurgy to clean the surface of metals, as well as to obtain pure metals from their ores. This occurs by converting them into chlorides, which are easily reduced. For example, titanium and zirconium are obtained. The acid is widely used in organic synthesis (hydrohalogenation reactions). Pure chlorine is also sometimes obtained from hydrochloric acid.

It is also used in medicine as a medicine mixed with pepsin. It is taken when the stomach acidity is insufficient. Hydrochloric acid is used in Food Industry as an additive E507 (acidity regulator).

Safety precautions

At high concentrations, hydrochloric acid is a caustic substance. When it comes into contact with the skin, it causes chemical burns. Inhaling hydrogen chloride gas causes coughing, suffocation, and in severe cases even pulmonary edema, which can lead to death.

According to GOST, it has a second hazard class. Hydrogen chloride is classified as a hazard category three out of four according to NFPA 704. Short-term exposure may result in serious temporary or moderate residual effects.

First aid

If hydrochloric acid gets on the skin, the wound should be washed generously with water and a weak solution of alkali or its salt (for example, soda).

If hydrogen chloride vapor gets into the respiratory tract, the victim must be taken out to Fresh air and inhale oxygen. After this, gargle, wash your eyes and nose with a 2% sodium bicarbonate solution. If hydrochloric acid gets into your eyes, then you should drip them with a solution of novocaine and dicaine with adrenaline.

DEFINITION

Hydrogen chloride(hydrochloric acid, hydrochloric acid) is a complex substance of inorganic nature that can exist in both liquid and gaseous states.

In the second case, it is a colorless gas, highly soluble in water, and in the first, it is a solution of a strong acid (35-36%). The structure of the hydrogen chloride molecule, as well as its structural formula, is shown in Fig. 1. Density - 1.6391 g/l (n.s.). The melting point is - (-114.0 o C), boiling point - (-85.05 o C).

Rice. 1. Structural formula and spatial structure of the hydrogen chloride molecule.

The gross formula of hydrogen chloride is HCl. As is known, the molecular mass of a molecule is equal to the sum of the relative atomic masses of the atoms that make up the molecule (we round off the values ​​of the relative atomic masses taken from D.I. Mendeleev’s Periodic Table to whole numbers).

Mr(HCl) = Ar(H) + Ar(Cl);

Mr(HCl) = 1 + 35.5 = 36.5.

Molar mass (M) is the mass of 1 mole of a substance. It is easy to show that the numerical values ​​of the molar mass M and the relative molecular mass M r are equal, however, the first quantity has the dimension [M] = g/mol, and the second is dimensionless:

M = N A × m (1 molecule) = N A × M r × 1 amu = (N A ×1 amu) × M r = × M r .

It means that molar mass hydrogen chloride is 36.5 g/mol.

The molar mass of a substance in the gaseous state can be determined using the concept of its molar volume. To do this, find the volume occupied under normal conditions by a certain mass of a given substance, and then calculate the mass of 22.4 liters of this substance under the same conditions.

To achieve this goal (calculation of molar mass), it is possible to use the equation of state of an ideal gas (Mendeleev-Clapeyron equation):

where p is the gas pressure (Pa), V is the gas volume (m 3), m is the mass of the substance (g), M is the molar mass of the substance (g/mol), T is the absolute temperature (K), R is the universal gas constant equal to 8.314 J/(mol×K).

Examples of problem solving

EXAMPLE 1

EXAMPLE 2

Hydrogen chloride (HC I )hazard class 3

A colorless gas with a pungent odor, heavier than air, liquefies at a temperature of –85.1 0 C, and solidifies at a temperature of –114.2 0 C. In air it smokes due to the formation of fog droplets with water vapor. Non-flammable, explosive when containers are heated. It dissolves well in water, less so in organic liquids. Under normal conditions, 450-500 volumes of gas are dissolved in one volume of water. A 27.5-38% solution of hydrogen chloride in water forms hydrochloric acid, and a 36% solution of hydrogen chloride in water forms concentrated hydrochloric acid.

Hydrogen chloride is used for the production of hydrochloric acid, vinyl chloride, alkyl chlorides, for the oxidative chlorination of organic compounds, the production of metal chlorides, hydrolytic alcohol, glucose, sugar, gelatin and glue, for dyeing fabrics, etching metals, in hydrometallurgical processes and electroplating. Hydrogen chloride is obtained as by-product during chlorination and dehydrochlorination organic compounds, as well as in the interaction of sodium chloride with sulfuric acid. Currently, it is produced synthetically by burning hydrogen in a stream of chlorine.

Hydrogen chloride is transported in railway and road tanks, containers and cylinders, which are temporary stored. Usually hydrogen chloride is stored in a liquefied state at ambient temperature under a pressure of its own vapors of 6-18 kgf/cm 2 in above-ground cylindrical horizontal tanks. Maximum storage volumes are 1.98 tons.

Maximum permissible concentration (MPC) hydrogen chloride in the air of populated areas: average daily - 0.02 mg/m 3, maximum single - 0.05 mg/m 3, in the air working area production premises - 5 mg/m3.Hydrogen chloride has a strong irritant effect on the respiratory system. Long-term exposure to low concentrations causes catarrh of the upper respiratory tract and rapid destruction of tooth enamel. Concentrations of 50-75 mg/m3 are difficult to tolerate; acute poisoning is accompanied by hoarseness, choking, and coughing. Concentrations of 75-150 mg/m 3 are intolerable, causing irritation of mucous membranes, conjunctivitis, a feeling of suffocation, and loss of consciousness.

When eliminating accidents associated with a leak (emission) of hydrogen chloride, it is necessary to isolate the dangerous area, remove people from it, stay to the windward side, avoid low places, enter the accident zone only in full protective clothing. Directly at the scene of the accident and at a distance of up to 50 meters from the source of contamination, work is carried out in insulating gas masks IP-4M, IP-5, IP-6 (using chemically bound oxygen), breathing apparatus ASV-2, DASV (using compressed air) KIP-8, KIP-9 (on compressed oxygen) and skin protection products (L-1, OZK, KIH-4, KIH-5, etc.). At a distance of more than 50 meters from the source, where the concentration of hydrogen chloride sharply decreases, skin protective equipment need not be used, and filtering ones are used to protect the respiratory system: large-sized industrial gas masks with boxes of grade B and BKF, small-sized with a box of grade B, civilian gas masks GP-5, GP-7, PDF-2D, PDF-2Sh complete with DPG-3 or respirators RPG-67, RU-60M with a box of brand V.

The presence of hydrogen chloride is determined:

In the air of an industrial zone with an OKA-T-N gas analyzer Cl , gas detector IGS-98-N Cl , universal gas analyzer UG-2 with a measurement range of 0-100 mg/m 3 , gas detector of industrial chemical emissions GPHV-2 in the range of 5-500 mg/m 3 .

In open space – with SIP “CORSAR-X” devices.

Indoors - with SIP devices "VEGA-M"

Neutralize hydrogen chloride the following alkaline solutions

5% aqueous solution of caustic soda (for example, 50 kg of caustic soda per 950 liters of water);

5% aqueous solution of soda powder (for example, 50 kg of soda some powder for 950 liters of water);

5% aqueous solution of slaked lime (for example, 50 kg of slaked lime per 950 liters of water);

5% water solution of caustic soda (for example, 50 kg of caustic soda per 950 liters of water);

When neutralizing hydrogen chloride, its vapors are precipitated by placing a water curtain (water consumption is not standardized); when neutralizing precipitated vapors, water or 5% aqueous solutions of caustic soda, soda powder, slaked lime, and caustic soda are used. To spray water or solutions, watering and fire trucks, auto-filling stations (ATs, PM-130, ARS-14, ARS-15), as well as hydrants and special systems available at chemically hazardous facilities, are used.

To dispose of contaminated soil at the spill site when hydrogen chloride is neutralized, the surface layer of soil is cut to the depth of contamination, collected and transported for disposal using earthmoving vehicles (bulldozers, scrapers, motor graders, dump trucks). The cut areas are covered with a fresh layer of soil and washed with water for control purposes.

Leader actions: isolate the danger zone within a radius of at least 50 meters, remove people from it, stay to the windward side, avoid low places. Enter the accident area only in full protective clothing.

Providing first aid:

In the contaminated area: rinse eyes and face generously with water, put on anti-vogaza, urgent withdrawal (removal) from the outbreak.

After evacuating a contaminated area: warming, rest, washing off the acid formed by the interaction of hydrogen chloride with water from open areas of the skin and clothing with water, abundantly washing the eyes with water, if breathing is difficult, apply heat to the neck area, subcutaneously - 1 ml. 0.1% atropine sulfate solution. Immediate evacuation to a medical facility.

Hydrogen chloride is a colorless gas heavier than air with a pungent odor, which consists of equal volumes of chlorine and hydrogen, formula: HCl

A mixture of chlorine and hydrogen gives a violent reaction and explodes even when sunlight, forming hydrogen chloride.

Hydrogen chloride itself is not a flammable gas.

In the laboratory you can obtain hydrogen chloride using concentrated sulfuric acid + table salt and heating this mixture.

Hydrogen chloride gas dissolves well in water, the solution itself is called.

At high concentrations, hydrochloric acid seems to smoke in the air, as hydrogen chloride is gradually released from the solution into the external moisture of the air. When heated, the release of hydrogen chloride becomes more intense.

Hydrochloric acid is widely used to remove rust from surfaces. However, this can only be done with the use of inhibitors (additives that slow down the reaction of the metal with the acid) so that the acid does not spoil the metal itself. Salts are also obtained from acid, used in medicine, etc. This acid is even secreted by our stomach to digest food, but the concentration there is very low (0.2-0.5%).

Salts of this acid are called chlorides. Chlorides are also generally soluble in water.

If you add silver nitrate (AgNO 3) to hydrochloric acid or its salt, a white cheesy precipitate forms. This precipitate is insoluble in acids, which always makes it possible to establish the presence of chloride ions.