Chemical Properties of Cadmium

Cadmium burns, when heated in air, to a brown oxide. It was said to retain its brilliancy at ordinary temperatures, but it tarnishes in ordinary air.

Cadmium volatilises before it acts on water, but it can be converted into oxide by heating a mixture of cadmium vapour and steam. The reaction

Cd+H₂O ⇔ CdO+H₂

is, however, reversible. If the metal is immersed in water a layer of hydrated oxide forms upon it.

Cadmium behaves towards acids very similarly to zinc. The heat of solution in aqueous hydrochloric acid has been determined thus -

Cd+2HCl.200H₂O = CdCl₂.400H₂O+H₂ + 17.230 Cal.

at 20° C. if the hydrogen is dry. The corresponding figure for moist hydrogen is 16.980 Cal.

Heated cadmium reacts more readily than zinc with sulphur dioxide, and is converted into a mixture of cadmium sulphate and sulphide.

Cadmium sulphide is produced when sulphurous acid acts on the metal. Sulphur is precipitated in the presence of hydrochloric or sulphuric acid, and the complete action may be complex. According to Fordos and Gelis, cadmium sulphite and hydrogen are first produced. The nascent hydrogen reduces the excess of sulphurous acid to hydrogen sulphide. The latter then precipitates some of the cadmium sulphite as sulphide. They obtained cadmium sulphite and sulphide by treating cadmium with sulphurous acid. Schutzenberger obtained the same products. Cadmium sulphide is also produced when cadmium is heated with sulphurous acid at 200° C. in closed vessels.