Chemical Properties of Chromium

Chemical Properties of Chromium are related with chromium activity. Chromium is oxidised only to a very slight extent by moist air at ordinary temperatures, but when heated to 2000° C. in oxygen it burns with scintillations of extreme brilliance, forming the sesquioxide, Cr₂O₃. In sulphur vapour at 700° C. and in hydrogen sulphide at 1200° C., the sulphide is formed; at the latter temperature the metal is attacked superficially by carbon dioxide, whilst on heating with carbon, crystalline carbides are obtained. With silicon and boron, the silicide and boride are respectively formed; anhydrous hydrogen chloride reacts at a red heat with the formation of crystalline chromous chloride, CrCl₂, chlorine similarly yielding chromic chloride, CrCl₃.

By hydrochloric acid the metal is attacked slowly in the cold, though more quickly on warming. Boiling concentrated sulphuric acid yields sulphur dioxide with the formation of a dark coloured solution; somewhat diluted acid yields hydrogen and chromous sulphate; fuming nitric acid has no action on chromium, neither has aqua regia. The metal is obtained in a passive state by exposure to air, concentrated nitric acid, or to other oxidising agents. The passivity has been ascribed to the formation of a superficial layer of an oxide, or possibly of gas, since, when rendered passive by means of nitric acid, the metal contains occluded oxygen and nitric oxide.

Chemical Properties of Chromium im powdered state are almost the same. Powdered chromium is slowly attacked by mercuric chloride in solution, with the formation of chromic chloride. Though unattacked by fused sodium carbonate, fused potassium nitrate and chlorate oxidise it vigorously. Pyrophoric chromium combines with nitrogen on heating.