HCL

What is HCL?

Hydrochloric acid is an aqueous solution of hydrogen chloride (HCl). At room temperature hydrogen chloride is a light yellow, corrosive, non-flammable gas, heavier than air, with a strongly irritating smell. When exposed to air hydrogen chloride forms dense white-coloured corrosive vapours. Hydrogen chloride has numerous uses. It is used, for example, to clean, treat and galvanise metals, tan leathers and in the refining and manufacture of a wide range of products. Hydrogen chloride can be formed during the burning of many plastics. When it comes into contact with water it forms hydrochloric acid. Both hydrogen chloride and hydrochloric acid are corrosive.

The physical properties of hydrochloric acid, such as melting and boiling points, density and pH depend on the concentration and molar concentration of HCL in the acid solution.

Hydrochloric acid (HCl) is obtained in the laboratory through the addition of sulphuric acid (H₂SO₄) to salt (NaCl) heating it to 150 °C.

In the chemical industry large amounts of hydrochloric acid are formed in organic reactions of chlorination of organic substances with basic chlorine.

Hydrochloric acid is used above all as a cheap, strong and volatile acid. The most well-known use is the desincrustation of limestone waste (calcium carbonate: CaCO₃).^[4] In this application the calcium carbonate is transformed into the more soluble calcium chlorate and carbon dioxide (CO₂) and water are released.

In organic chemistry hydrochloric acid is sometimes used in the synthesis of organic chlorines – either by replacement of a hydroxyl group by an alcohol or by adding hydrochloric acid to an alkene although these reactions often do not occur in a very selective way.

How can HCL affect us?

Hydrogen chloride is an irritant and corrosive to any material with which it comes into contact. Brief exposure at low levels causes throat irritation. Exposure at higher levels can cause wheezing when breathing, narrowing of the bronchioles, blue colour skin, liquid accumulating in the lungs and even death.

The mixture of acids with commonly used oxidising agents, such as bleach, produces the toxic gas chlorine. Depending on the concentration hydrogen chloride can cause from slight irritation to serious burns on the eyes and skin.

Despite these characteristics the human stomach contains approximately 3 % of hydrochloric acid. There it helps to denature the proteins and performs an important role as a co-enzyme to pepsin in digestion. It also helps in hydrolysis of the polysaccharides present in food. It is secreted by the parietal cells. These contain an extensive secretion network where HCL is secreted towards the stomach lumen.