Chromium 24 Cr 51.9961(6)   Switch element to... actinium aluminium aluminum americium antimony argon arsenic astatine barium berkelium beryllium bismuth bohrium boron bromine cadmium caesium calcium californium carbon cerium cesium chlorine chromium cobalt copper curium darmstadtium dubnium dysprosium einsteinium erbium europium fermium fluorine francium gadolinium gallium germanium gold hafnium hassium helium holmium hydrogen indium iodine iridium iron krypton lanthanum lawrencium lead lithium lutetium magnesium manganese meitnerium mendelevium mercury molybdenum neodymium neon neptunium nickel niobium nitrogen nobelium osmium oxygen palladium phosphorus platinum plutonium polonium potassium praseodymium promethium protactinium radium radon rhenium rhodium roentgenium rubidium ruthenium rutherfordium samarium scandium seaborgium selenium silicon silver sodium strontium sulfur sulphur tantalum technetium tellurium terbium thallium thorium thulium tin titanium tungsten ununbium ununhexium ununoctium ununpentium ununquadium ununtrium uranium vanadium xenon ytterbium yttrium zinc zirconium Go adjacent...       V Cr Mn Nb Mo Tc

The essentials

Description 

Here is a brief description of chromium.

• Standard state: solid at 298 K
• Colour: silvery metallic
• Classification: Metallic
• Availability:

This sample is from The Elements Collection, an attractive and safely packaged collection of the 92 naturally occurring elements that is available for sale.

Chromium is steel-gray, lustrous, hard, metallic, and takes a high polish. Its compounds are toxic. It is found as chromite ore. Siberian red lead (crocoite, PrCrO₄) is a chromium ore prized as a red pigment for oil paints.

WebElements movies
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The picture above shows the result of burning ammonium dichromate, (NH4)2Cr2O7, containing pellets of mercuric thiocyanate (HgCNS). This is a large scale version of the indoor firework "Serpents in te grass". Do not attempt this reaction unless are a professionally qualified chemist and you have carried out a legally satisfactory hazard assessment. Improperly done, this reaction is dangerous! Select a movie icon to see the volcano and serpents (lighting not great - sorry).

Nearing Zero cartoon included by kind permission of Nick Kim.

Emerald is a form of beryl (a beryllium aluminium silicate) which is green because of the inclusion of a little chromium into the beryl crytal lattice in place of some of the aluminium ions. Similarly, traces of chromium incorporated into the crystal lattice of corundum (crystalline aluminium oxide, Al₂O₃) as a replacement for some of the Al³⁺ ions results in another highly coloured gem stone, in this case the red ruby.

Isolation

It is not normally necessary to make chromium in the laboratory as it is so readily available commercially. The most useful source of chromium commercially is the ore chromite, FeCr₂O₄. Oxidation of this ore by air in molten alkali gives sodium chromate, Na₂CrO₄ in which the chromium is in the +6 oxidation state. This is converted to the Cr(III) oxide Cr₂O₃ by extraction into water, precipitation, and reduction with carbon. The oxide is then further reduced with aluminium or silicon to form chromium metal.

Cr₂O₃ + 2Al → 2Cr + Al₂O₃

2Cr₂O₃ + 3Si → 4Cr + 3SiO₂

Another kind of isolation is by electroplating processes. This involves the dissolution of Cr₂O₃ in sulphuric acid to give an electrolyte used for chromium electroplating.

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