Hydrochloric acid is a corrosive substance produced when hydrogen chloride gas dissolves in water up to concentrations of 39 percent HCl by weight. Also called muriatic acid, it easily dissolves non-precious metals. Its industrial applications include the treatment of metals, food processing, and the production of fertilizers, plastics and detergents.
Alkali metals potassium, sodium, and lithium belong to Group 1 of the Periodic Table and have one electron in their outer shells. They are highly reactive, silver-coloured metals that are soft enough to cut with a knife. These metals float on water and react violently with it to produce hydrogen gas and an alkaline solution. They also react violently with hydrochloric acid to produce a salt – potassium, sodium, or lithium chloride – and hydrogen gas. The hydrogen gas may ignite during the reaction.
Alkaline earth metals
A part of Group 2 of the Periodic Table, alkaline earth metals calcium, magnesium and strontium have two electrons in their outer shells and are more stable than Group 1 elements. They react with hydrochloric acid to produce a chloride salt and hydrogen gas. But they do so less violently than Group 1 metals and can therefore be used safely for school chemistry demonstrations.
Iron oxides haematite, wustite, and magnetite form a crust on steel – called scale – during the hot rolling process. Hydrochloric acid is used for pickling the steel, a process that dissolves the oxide scale. When pure iron is added to the pickling solution it speeds up the process and reacts with the acid to create a solution of ferrous chloride and water.
Tantalum is a non-reactive metal used widely in surgical implants and electronic circuitry as a substitute for platinum. Chemists regard it as the most corrosion resistant metal that is commercially available. According to experiments conducted by Danish metals producer Tantaline, this metal will eventually react with hydrochloric acid. But the reaction occurs at temperatures of 200ºC or higher, and using a hydrochloric acid concentration of 35 percent by weight.
Precious metals such as gold and platinum don't react with hydrochloric acid alone. But when hydrochloric acid is combined with nitric acid in the ratio 3 to 1, it creates nitrosol chloride, commonly called aqua regia. This solution dissolves gold and other precious metals from ores, alloys or electronic circuit boards.