Chromium

Chromium, Cr, is a transition metal element, found in Group VIa of the periodic table.

Discovery

Chromium was discovered by L N Vauquelin in 1797AD.

Occurrence

Chromium does not occur in elemental form, but is found in Chrome Ochre, Cr2O3.

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..


Extraction

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


Properties


Reactions

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


Uses

Chromium, Cr, is an important component

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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