Description
Molar mass: 36.46/mol
Solution pH: concentrated HCl, 32-37% in water: pH < 0
Hydrochloric acid (HCl) is an inorganic chemical compound known for its strength and corrosive properties. Although it is colorless in itself, it can sometimes have a yellow tint resulting from the presence of iron ion impurities. Sometimes, the term ‘hydrochloric acid’ is also used to refer to the solution of hydrogen chloride in polar solvents other than water, such as acetone. In diluted form, it occurs in the stomachs of mammals. It is classified as a dangerous material with the number UN 1789 according to the ADR regulations.
Typically, hydrochloric acid is obtained through the absorption of hydrogen chloride gas in water. Since this is a highly exothermic process, it is carried out in a surface absorber in so-called turyls, above the water surface. Hydrogen chloride itself can be obtained by the reaction of sulfuric acid with sodium chloride, i.e. rock salt. In addition, it can be formed from the combustion of hydrogen in chlorine, as well as be a by-product of various industrial processes (e.g. chlorination of organic compounds). In industry, hydrochloric acid is formed as a by-product of the production of polyvinyl chloride (PVC). This process requires the production of vinyl chloride (VCM), the basic monomer for the production of PVC. To achieve this, chlorination of ethylene is used, which then reacts with chlorine to form 1,2-dichloroethane (EDC). This occurs in the presence of a catalyst. EDC is then pyrolyzed, as a result of which vinyl chloride and gaseous hydrogen chloride are obtained. The gaseous hydrogen chloride is then absorbed in water, forming hydrochloric acid.
Because hydrogen chloride undergoes almost complete dissociation, hydrochloric acid is one of the strongest inorganic acids. However, it has no oxidizing properties and is volatile, so it is less corrosive than strong oxygen acids (nitric, sulfuric). Hydrochloric acid is often referred to as “fuming” because hydrogen chloride gas escapes from concentrated acid, which reacts with moisture in the air to form fog. Below a concentration of 30%, hydrochloric acid does not exhibit this property. In addition, hydrochloric acid reacts with metals located above hydrogen in the reactivity series, forming metal chlorides and releasing hydrogen. It is able to dissolve most metals, except noble metals. It also reacts with metal oxides, forming salts and water, as well as with salts of weaker acids. As an acid, it neutralizes bases, forming water and metal chloride. HCl reacts with ammonia, forming ammonium chloride. In a mixture with nitric acid, it forms aqua regia, capable of dissolving gold and platinum. It is also often used as an acid catalyst in reactions such as esterification and hydrolysis.
