A class book of elementary chemistry / by W.W. Fisher.

  • Walter William Fisher
Date:
1897
Catalogue details

Licence: Public Domain Mark

Credit: A class book of elementary chemistry / by W.W. Fisher. Source: Wellcome Collection.

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    manner already described, is converted into perman- ganate by boiling, or by the action of an acid:— 3K2Mn0, + 3H,0 = 2KMn04 + Mn02 + 4HK0 + H20. The potassium manganate with water forms potassium permanganate, manganese dioxide, potash and water, and the manganese oxide precipitates as a dark brown powder. With an acid no precipitation takes place:— 5K2M11O4 + 4H2SO4 = 4KMn04 + MnS04 + 3K2S04 + 4H2 0. Potassium permanganate is formed, with manganous sulphate, and potassium sulphate. The pure salt is obtained by evaporation and crystallisation ; it forms needle-like crystals of bronzy lustre, and is in every way a more stable compound than the manganate. Crude solutions of manganate and permanganate are used for disinfecting purposes (Condy’s fluid). Since permanganates contain much oxygen, they are useful as oxidising agents ; and accordingly are de-oxidised by reducing agents, such as those capable of reducing chromates. For example, a solution of permanganate mixed with a feiTous salt loses its red colour, the reaction being, as follows :— 2 KMn O4 + 3 H2 SO4 = 2 Mn SO4 + K2 SO4 + [O5] + 3 H2 0. Two molecules of permanganate with sulphuric acid become changed into manganous sulphate, potassium ^ sulphate, and flve atoms of available oxygen, which is, of course, taken up by the ferrous salt in its conversion to a ferric salt:— 2FeS04 + H2S04+[0] = Fe2 (804)3+ H2O. Cuprous salts, mercurous salts, and stannous salts; sulphurous acid, hydrogen sulphide, potassium nitrite, and potassium iodide in a similar manner reduce and decolorise a solution of the permanganate.