What Is Potassium Dichromate?
Potassium dichromate is an inorganic compound with the chemical formula K2Cr2O7. Naturally, potassium dichromate occurs as the rare mineral lopezite in nitrate deposits of the Atacama Desert in Chile and in the Bushveld igneous rock complex in South Africa. It is one of the most environmentally hazardous substances, being a hexavalent chromium with an oxidation number of +6 for chromium.
Potassium dichromate is produced using chromite as a raw material. First, the chrome ore is crushed by baking, then calcium oxide and potassium carbonate are added, heated strongly, and further air-oxidized. Then sulfuric acid is added to produce potassium dichromate as crystals.
Uses of Potassium Dichromate
Potassium dichromate has several uses including in photo printing, match igniters, and as a raw material for explosives. In chemistry, it serves as a raw material in the production of dichromates and chromates. Its strong oxidizing properties make it useful in organic synthesis and as an analytical reagent.
Although it has important applications, potassium dichromate is toxic and requires careful handling. It is designated as a deleterious substance under the Poisonous and Deleterious Substances Control Law.
Properties of Potassium Dichromate
Potassium dichromate appears as orange-red columnar crystals. It has a melting point of 398°C and decomposes at 500°C due to oxygen formation. It is insoluble in ethanol but soluble in water.
Adding alkali to an orange-red dichromate solution forms chromate ions and yields a yellow solution. Treatment with cold sulfuric acid produces red crystals of chromic anhydride (CrO3). Heating potassium dichromate with concentrated sulfuric acid generates oxygen.
Structure of Potassium Dichromate
Potassium dichromate, also known as potassium bichromate, has a triangular pyramidal crystal structure and a triclinic coordination structure. Its molecular weight is 294.19, and its density is 2.676 g/cm3. It ionizes when dissolved in water.
Typically, potassium dichromate is obtained by reacting potassium chloride with sodium dichromate or by synthesizing it from potassium chromate through roasting chromate ore with potassium hydroxide.
Other Information on Potassium Dichromate
1. Reaction of Potassium Dichromate
In organic chemistry, potassium dichromate is a milder oxidizer than potassium permanganate. It oxidizes primary alcohols to aldehydes and, under certain conditions, to carboxylic acids. Secondary alcohols are converted to ketones. The color change in aqueous solutions can distinguish between ketones and aldehydes.
2. Hazards of Potassium Dichromate
Potassium dichromate is a potent sensitizer and can cause chronic dermatitis. It is toxic to aquatic organisms and poses risks to human health, including carcinogenicity, corrosiveness, and reproductive harm.