Manganese oxide
Manganese oxide (MnO2) is a chemical compound also known as manganese dioxide. It has a blackish or brown color. It is the main source for extracing the metal manganese. It can also be used for production of manganates, both MnO42- and MnO4-.A green substance was obtained after melting manganese oxide with an alkaline salt and adding oxidizing agents like saltpeter (sodium nitrate NaNO3) or potassium perchlorate (KClO4). This substance dissolves in cold water, giving a dark green color. Potassium manganate (K2MnO4), a salt in dark green crystalized rombic prisms (dark green), was formed after vacuum distilling with a metal "finish". Potassium manganate is soulable in lye ONLY, otherwise it will disproportionate into potassium permanganate (KMnO4-) and manganese oxide (MnO2).
Potassium manganate is converted into potassium permaganate in aqueous acidic solution:
3MnO42- + 4H+ --> 2MnO4- + MnO2) + 2H2O
MnO4(-) has a purple color
MnO4(2-) has a green color
MnO2 is used as a catalyst in the laboratory preparation of oxygen from potassium chlorate, one of the classical experiments of elementary chemistry classes. The procedure consists of merely heating potassium chlorate and manganese dioxide together in a hard glass container and collecting the gas over water. See oxygen, manganese and potassium chlorate for precautions.
Eighteenth-century British chemists referred to MnO2 simply as manganese. Elemental manganese was known as reglus of manganese.
Ancient cave painters sometimes used MnO2 as black paint
