Chromium Alum – Chromium (III) Potassium Sulphate – 99 % – 100 g
Chemical formula: KCr(SO4)2.12H2O
Synonyms: chromium potassium sulphate dodecahydrate, chromium alum
Amount: 100 g
Appearance and odour: purple crystalline material without appreciable odour
Grade: 99 %
Packaging: professional wide necked, white HDPE bottle with blue conical seal cap and tamper ring. Labelled. Bottle and cap are UN approved and reusable.
Description and uses: a double salt of chromium (III) sulphate and potassium sulphate used as a dye mordant and tanning agent). It is a primary source of soluble chromium salt. Well soluble in water it is an ideal substance for crystal growing (above 50 C aqueous solutions go from dark violet to green, a non-crystallisable form). It forms regular octahedral crystals with flattened corners and can be grown into very large crystals with some patience. Mixed crystals with layered aluminium alum or ferric alum can also be grown.
With strong alkali chromium hydroxide (Cr(OH)3) is precipitated but due to chromium’s amphoterism this dissolves in excess alkali to blue-green chromite (Cr(OH)4(-)), showing strong similarity with aluminium in that respect. Chromite can be oxidised easily with hydrogen peroxide, to yellow chromate (CrO4(2-)), a Cr VI compound. On acidification the dichromate ion – Cr2O7(2-) is then formed.
Cr III compounds can be reduced by means of zinc powder (available from this seller) in acidic conditions, to form the poorly stable Cr2+ ion.
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