Physical Properties of Potassium Dichromate

Potassium dichromate is characteristically an orange-red crystalline solid, melting at 671 K. Its aqueous solubility behaviour is strongly temperature dependent: the compound is only moderately soluble in cold water, but its solubility rises considerably in hot water, a property that is directly exploited in its manufacturing purification (section 4.4.2.1), where the compound is deliberately crystallised out of a HOT saturated solution upon cooling.

On strong heating, potassium dichromate undergoes thermal decomposition, breaking down into potassium chromate (K₂CrO₄), chromium(III) oxide (Cr₂O₃) and molecular oxygen gas: 4K₂Cr₂O₇ →(Δ) 4K₂CrO₄ + 2Cr₂O₃ + 3O₂↑. Because this decomposition process releases toxic, chromium-containing fumes into the atmosphere -- a genuine occupational-health and environmental hazard associated with heating chromium(VI) compounds -- potassium dichromate has, in many industrial applications where high-temperature use would otherwise be required, been substantially replaced by sodium dichromate, which serves a broadly similar chemical purpose while offering some practical/ …