Hydrogen chloride - what is it? Hydrogen chloride is a colorless gas with a pungent odor. It readily dissolves in water, forming hydrochloric acid. The chemical formula of hydrogen chloride is HCl. It consists of a hydrogen atom and chlorine connected by a covalent polar 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 mentioned above, in the normal state, 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, forming thick vapor clouds. For this reason, hydrogen chloride is said to "smoke" in air. If this gas is cooled, then at -85 ° C it liquefies, and by -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).
HCl solution in water is called hydrochloric acid. She isis 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. Other physical properties also depend on it: density, viscosity, melting and boiling points.
Chemical properties
Hydrogen chloride itself usually does not react. Only at high temperatures (over 650 °C) does it react with sulfides, carbides, nitrides and borides, as well as transition metal oxides. In the presence of Lewis acids, it can interact with boron, silicon, and germanium hydrides. But its aqueous solution is much more chemically active. By its formula, hydrogen chloride is an acid, so it has some of the properties of acids:
Interaction with metals (which are in the electrochemical series of voltages up to hydrogen):
Fe + 2HCl=FeCl2 + H2
Interaction with amphoteric and basic oxides:
BaO + 2HCl=BaCl2 + H2O
Interaction with alkalis:
NaOH + HCl=NaCl + H2O
Interaction with some s alts:
Na2CO3 + 2HCl=2NaCl + H2O + CO 2
When interacting with ammonia, an ammonium chloride s alt is formed:
NH3 + HCl=NH4Cl
But hydrochloric acid does not interact with lead due to passivation. This is due to the formation of a layer of lead chloride on the metal surface, which is insolublein water. Thus, this layer protects the metal from further interaction with hydrochloric acid.
In organic reactions, it can add on multiple bonds (hydrohalogenation reaction). It can also react with proteins or amines, forming organic s alts - hydrochlorides. Artificial 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.
Receive
Earlier in industry, hydrochloric acid was produced by reacting sodium chloride with acids, usually sulfuric:
2NaCl + H2SO4=2HCl + Na2SO 4
But this method is not efficient 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 stream to the flame in which the interaction takes place. Hydrogen is supplied in a slight excess so that all the chlorine reacts and does not contaminate the resulting product. Hydrogen chloride is then dissolved in water to form hydrochloric acid.acid.
In the laboratory, more diverse methods of preparation are possible, for example, the hydrolysis of phosphorus halides:
PCl5 + H2O=POCl3 + 2HCl
Hydrochloric acid can also be obtained by hydrolysis of crystalline hydrates of certain metal chlorides at elevated temperatures:
AlCl3 6H2O=Al(OH)3 + 3HCl + 3H2O
Also, hydrogen chloride is a by-product of the chlorination reactions of many organic compounds.
Application
Hydrogen chloride itself is not used in practice, as it very quickly absorbs water from the air. Almost all of the hydrogen chloride produced is used to produce hydrochloric acid.
It is used in metallurgy to clean the surface of metals, as well as to obtain pure metals from their ores. This happens by converting them into chlorides, which are easily restored. For example, titanium and zirconium are obtained. The acid has been widely used in organic synthesis (hydrohalogenation reactions). Also, pure chlorine is sometimes obtained from hydrochloric acid.
It is also used in medicine as a medicine mixed with pepsin. It is taken with insufficient acidity of the stomach. Hydrochloric acid is used in the food industry as an additive E507 (acidity regulator).
Safety
At high concentrations, hydrochloric acid is corrosive. Contact with skin causes chemical burns. Inhalation of hydrogen chloride gas causescoughing, choking, 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 under NFPA 704 as a third of four hazard categories. Short-term exposure may result in severe temporary or moderate residual effects.
First Aid
If hydrochloric acid gets on the skin, the wound should be washed with plenty of water and a weak solution of alkali or its s alt (for example, soda).
If hydrogen chloride vapor enters the respiratory tract, the victim must be taken out to fresh air and inhaled with oxygen. After that, rinse your throat, rinse your eyes and nose with 2% sodium bicarbonate solution. If hydrochloric acid gets into the eyes, then after that it is worth dripping them with a solution of novocaine and dicaine with adrenaline.
