Chemical elements
  Potassium
    Isotopes
    Energy
    Preparation
    Physical Properties
    Chemical Properties
      Potassium hydride
      Potassium fluoride
      Potassium hydrogen fluoride
      Potassium chloride
      Potassium bromide
      Potassium iodide
      Potassium hypochlorite
      Potassium chlorate
      Potassium perchlorate
      Potassium hypobromite
      Potassium bromate
      Potassium perbromate
      Potassium hypoiodite
      Potassium iodate
      Potassium periodate
      Potassium monoxide
      Potassium peroxides
      Potassium hydroxide
      Potassium monosulphide
      Potassium sulphide
      Potassium polysulphides
      Potassium hydrogen sulphide
      Potassium sulphite
      Potassium hydrogen sulphite
      Potassium pyrosulphite
      Potassium sulphate
      Potassium hydrogen sulphate
      Potassium pyrosulphate
      Potassium persulphate
      Potassium thiosulphate
      Potassium dithionate
      Potassium trithionate
      Potassium tetrathionate
      Potassium pentathionate
      Potassium hyposulphite
      Potassium selenides
      Potassium selenate
      Potassium tellurides
      Potassium tellurate
      Potassium nitride
      Potassium hydrazoate
      Potassamide
      Potassium hyponitrite
      Potassium nitrite
      Potassium nitrate
      Potassium phosphides
      Potassium hypophosphite
      Potassium orthophosphates
      Potassium pyrophosphate
      Potassium metaphosphate
      Potassium arsenite
      Potassium arsenates
      Potassium carbide
      Potassium carbonate
      Potassium sodium carbonate
      Potassium bicarbonate
      Potassium hydrogen carbonate
      Potassium percarbonate
      Potassium thiocarbonate
      Potassium cyanide
      Potassium thiocyanate
      Potassium silicates
      Potassium fluosilicate
      Potassium silicofluoride
      Potassium hypoborate
      Potassium borates
      Dipotassium tetraborate
      Potassium perborates
      Potassium oxalate
    PDB 1a3w-1dul
    PDB 1dz4-1j95
    PDB 1jbr-1lqp
    PDB 1lrt-1o07
    PDB 1o76-1qb9
    PDB 1qj5-1t86
    PDB 1t87-1vq9
    PDB 1vqk-1yj9
    PDB 1yjn-2aop
    PDB 2apo-2f4v
    PDB 2fbw-2hg9
    PDB 2hh1-2oij
    PDB 2oiy-2uxb
    PDB 2uxc-2x20
    PDB 2x21-3c0y
    PDB 3c0z-3dix
    PDB 3diy-3f5w
    PDB 3f7j-3hqo
    PDB 3hqp-3l01
    PDB 3l0u-3oi5
    PDB 3oia-3r9b
    PDB 3rde-4e6k
    PDB 4edj-8gep

Potassium sulphide, K2S






If a solution of caustic potash is saturated with sulphuretted hydrogen, so much of this is absorbed that the salt KHS, potassium hydrosulphide or the acid salt of sulphuretted hydrogen, is formed. By evaporation it can be obtained as a very deliquescent salt, containing ½H2O of crystallisation. If as much caustic potash is added as had been originally taken, and the solution evaporated, potassium sulphide, K2S, which is also very soluble, can be obtained with 5H2O of crystallisation. Anhydrous potassium sulphide is obtained by the reduction of potassium sulphate with pure charcoal: K2SO4 + 4C = K2S + 4CO. It is, however, very difficult to obtain a pure product, because the fused potassium sulphide attacks vessels of all kinds and becomes contaminated with the constituents of these.

The aqueous solution of potassium sulphide has a strongly alkaline reaction, and for the most part does not contain the ions K and S'. On the contrary, the latter react with the solvent water and form HS' and OH', so that the solution contains hydroxidion in large quantity. Here, as in all such cases, we are dealing with a chemical equilibrium in which all possible ions are present - sulphidion, S', therefore, as well; the amount of the latter is, however, very small.

The solutions of potassium sulphide rapidly oxidise in the air, the sulphide being converted into the potassium salts of the oxygen acids of sulphur. In the first instance, thiosulphanion is formed from the ion HS' by the absorption of oxygen: 2HS' + 2O2 = S2O3' + H2O.

In analytical chemistry, potassium sulphide is employed in order to obtain those sparingly soluble metallic sulphides which are decomposed by acids: e.g. K2S + FeCl2 = FeS + 2KCl. For this purpose, it is of no consequence that only a small amount of sulphidion is present in the solution, for when this is removed in the precipitate, a fresh quantity is immediately formed from HS' and OH'. For the above reaction, however, potassium sulphide is less used than the similarly acting ammonium sulphide, since the latter, or its products of transformation, can be much more readily removed from the analysis than can potassium sulphide.

If a solution of potassium sulphide is warmed with sulphur, large quantities of the latter are taken up, and the potassium salts of the ions S4' and S5' are formed, according to the amount of sulphur dissolved. They are all characterised by the fact that they give yellow-red solutions. If the liquids be poured into hydrochloric acid, the corresponding acids H2S4 and H2S5 separate out as oily liquids, which very readily decompose into sulphur and sulphuretted hydrogen, and are not known in the pure state. If, on the other hand, the hydrochloric acid is added to the sulphide solutions, sulphur and sulphuretted hydrogen are immediately obtained. The former is very finely divided, and constitutes milk of sulphur.

The peculiar difference of these two reactions is due to the fact that, in the first case, the acids formed, H2S2 to H2S5, are always in contact with the acid liquid; in the second case, with the liquid containing potassium sulphide. The latter, however, acts catalytically on the poly sulphides of hydrogen, and accelerates their decomposition into sulphuretted hydrogen and sulphur.


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