Chromium potassium sulphate extra pure

Chromium potassium sulphate extra pure, also known as chrome alum or chromium(III) potassium sulfate dodecahydrate, has the formula KCr(SO₄)₂·12H₂O. It appears as violet or red-violet crystalline powder or crystals, odorless, with a molecular weight of 499.40 g/mol, density of 1.83 g/cm³, and melting point around 89°C. The 'extra pure' grade meets high analytical standards (e.g., assay 99-102% by iodometry, low impurities like Cl ≤0.002%, heavy metals ≤0.01%) for laboratory use.​

It is highly soluble in water, efflorescent (loses water upon exposure to air), and forms octahedral [Cr(H₂O)₆]³⁺ complexes. Produced by reducing potassium dichromate with SO₂ in sulfuric acid or from ferrochromium, it exhibits low pH (around 3 in solution) and is stable under normal conditions but incompatible with strong reducers.​

Commonly used in leather tanning (chrome-tan liquors), as a mordant in textile dyeing, in photography fixing baths, and ceramics. It is irritant (skin/eye) and toxic by ingestion, requiring handling with gloves and eye protection