Hydrochloric acid is a strong mineral acid with a long history, which is used for many different industrial applications. It is a monoprotic acid, which means that it only gives one hydrogen ion (proton) when it is ionised in solution. It is a solution of hydrogen chloride, which is a gas at room temperature and pressure, but is very soluble in water.The History of Hydrochloric Acid
Hydrochloric acid was used by alchemists in the Middle Ages, when it was a constituent of Aqua Regia, with phosphoric acid. When it was first isolated, in the 16th Century, it was known as muriatic Acid, which has the meaning of 'pertaining to salt or brine', because it was produced by adding vitriol ( sulfuric acid) to salt ( sodium chloride). Its industrial production began during the Industrial Revolution, initially as a bi-product in the manufacture of sodium carbonate.
Manufacture of Hydrochloric Acid
Annually, global industry manufactures more than 20 million tonnes of hydrochloric acid. Many of the current methods of manufacture of the acid produce a bi-product of another process. For example, when brine or sodium chloride solution is electrolysed, sodium hydroxide is one product, and hydrogen and chlorine gases are evolved, which are reacted to form hydrogen chloride gas, which is dissolved in water to make hydrochloric acid.
Another example is in the chlorination of organic compounds. Chlorine gas is used, which displaces a hydrogen atom in the organic compound, with the bi-product being hydrogen chloride gas. A further source of hydrogen chloride is in the incineration of chlorinated waste.
Uses of Hydrochloric Acid
Hydrochloric acid is used in the steel industry in a process known as pickling, which effectively cleans up rusty metal. The acid is also used in the production of organic compounds such as vinyl chloride and dichloroethane which are used in the manufacture of PVC, bisphenol A, used in the manufacture of polycarbonate, and many pharmaceutical products.
It is also used in a range of inorganic processes, including the production of iron(III) chloride and polyaluminium chloride, which are used as flocculation and coagulation agents in water treatment. It is also used in the production of nickel (II) chloride for electroplating and zinc chloride for galvanising and battery manufacture. The acid is also used to clean bricks and etch concrete in the building industry, and in many household cleaning products.
Safe Use of Hydrochloric Acid
Hydrochloric acid is commonly produced and transported at a concentration of 38 percent any higher and there is too much evaporation. However, at this concentration the acid is extremely corrosive and must be handled with great care and personal protective equipment must be worn, including gloves, protective clothing and eye protection.
Hydrochloric Acid, Information, on hydrochloric-acid.co.uk , accessed 4th January 2011