Chromium, Cr, is a transition metal element, found in
Group VIa of the
- Atomic Number : 24
- Relative Atomic Mass : 51.996
Chromium was discovered by L N Vauquelin in 1797AD.
Chromium does not occur in elemental form, but is found in Chrome
The principal ores are Chromite, Fe(CrO2)2, and
Crocoisite, PbCrO4, is also important as a source.
Chromium is a trace component in semiprecious stones, emerald,
jade, serpentine, etc..
Chromium is made commercially by the Thermite Process, where Chromic
Oxide is reduced by the stoichiometric amount of Silicon and
Quick Lime in an electric arc furnace.
2 Cr2O3 + 3 Si + 3 CaO ==> 4 Cr + 3 CaSiO3
- Chromium is a bluish-white metal, which can take a brilliant polish.
- Chromium is a soft metal.
- Chromium containing a small amount of Carbon is one of the
- Chromium is very stable in air, and is used as an electroplated
surface to protect more reactive metals from corrosion.
Chromium is attacked slowly by dilute hydrochloric acid to form blue
solutions of chromous salts.
Cr + HCl ==> CrCl2 + H2
The chromous salt turns green on standing due to its oxidation in air
to chromic salts.
4 Cr + 4 HCl + O2 ==> 4 CrCl3 + 2 H2O
Chromium, Cr, is an important component
- in steels, in particular Ferrochrome (i.e. an alloy containing 40%
to 80% Chromium, Cr with Iron, Fe),
- in Chrome Vanadium Steels, used for tools,
- in Nichrome (i.e. an alloy containing 10% to 25% Chromium and 50%
to 70% Nickel),
- in Stellite (i.e. an alloy of Chromium, Cobalt, and Tungsten) used
for surgical instruments,
- as a plating metal on account of its resistance to corrosion, and
- as its salts in the glass industry, in pottery and as a mordant
Detection and Analysis
Chromium is detected by the deep blue colouration imparted to
ethereal solution over an aqueous test solution containing
the substance under test with hydrogen peroxide which has been
acidified with sulphuric acid.
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