Page 40 - Curriculum Visions Dynamic Book

Cadmium
Cadmium is a soft silvery-white metal,
much like zinc. The name cadmium
comes from the Latin name cadmia fornacum. This means “furnace zinc” because it was
first discovered as a part of zinc ore.
Cadmium is almost always found associated with zinc and is refined along with zinc from zinc ore. The ore sphalerite contains about one-fifth of one per cent of cadmium.
Cadmium finds widespread use as a catalyst, and its salts are used as colouring pigments in the ceramics industry: cadmium sulphides are yellow.
Cadmium reacts with acids to produce soluble cadmium salts.
Test for cadmium compounds
If hydrogen sulphide is bubbled through a solution of cadmium salts, bright yellow cadmium sulphide is precipitated. This is
used as a test for cadmium.
 Hydrogen sulphide solution is added to cadmium sulphate, resulting in a yellow precipitate of cadmium sulphide.
Cadmium-plating
Cadmium is a reactive metal that can be used in the same way as zinc to plate steel. A rare metal like cadmium is used in place of zinc because, unlike zinc, it will not be attacked by alkalis such as caustic soda. Also, cadmium
can be soldered; zinc cannot. Cadmium is much more
expensive than zinc, so the articles to be plated with cadmium are usually restricted to those that will be in corrosive environments, such as chemical works. Nuts and bolts that are very liable to seize up tight unless they are galvanised are often plated with cadmium.
Cadmium has a low coefficient of friction, so it is also used to coat some bearings.
EQUATION: Testing for cadmium with hydrogen sulphide
Hydrogen sulphide + cadmium sulphate ➪ cadmium sulphide + sulphuric acid
H2S(g) + CdSO4(aq)
➪ CdS(s) + H2SO4(l) 40
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