Hydrochloric acid is a clear, colorless to slightly yellow, highly pungent solution of hydrogen chloride (HCl) in water. It is a highly corrosive acid with many industrial uses. It is a monoprotic acid and is least likely to undergo an interfering oxidation-reduction reaction compared to other industrial acids. It is one of the least hazardous strong acids to handle despite its acidity as it consists the non-reactive and non-toxic chloride ion. Intermediate-strength hydrochloric acid solutions are quite stable upon storage, and their concentrations are maintained overtime. These attributes, together with the fact that it is available as a pure reagent, make hydrochloric acid an excellent acidifying reagent.
The simplest method for producing hydrogen chloride is direct synthesis from the elements, hydrogen (H) and chlorine (Cl), which yields a very pure product. Industrial production involves the use of a burner. Chlorine and hydrogen are fed by separate concentric tubes into the combustion chamber. After ignition, the chlorine burns in the hydrogen at more than 2000∘C. A cooling section is connected to the combustion chamber to collect the hydrogen chloride formed.
Hydrochloric acid is used to acidify cornstarch. It is also used in other food processing applications including the production of hydrolyzed vegetable protein and soy sauce. It is used in acidulating crushed bones for the manufacture of gelatin and as an acidifier for products such as sauces, vegetable juices and canned goods. Hydrochloric acid is used in the production of artificial sweeteners.
Hydrochloric acid is used in the production of chlorides, in hydrochlorination process, polymerization process, and isomerization process. It is also used for refining ore in the production of tin and tantalum, for pickling and cleaning of metal products, in electroplating, in removing scale from boilers and for the neutralization of basic systems.
HCl is used to adjust the pH of intermediates, final product and wastewater. It is also used in the oil industry in the acidification (activation) of petroleum wells. It is used in the production of lysine, choline chloride (both used primarily as animal feed additives) and citric acid.