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 hydroxide, KOH






The Potassium hydroxide, KOH can be prepared by methods similar to those employed for the corresponding sodium derivative. The chief processes are the electrolysis of the chloride, and the interaction of the carbonate or sulphate in aqueous solution with slaked lime. In the sulphate process, evaporation of the mother-liquid yields the anhydrous hydroxide, the monohydrate, or the di-hydrate, the formation of each product depending on the concentration. For laboratory use, the substance can be prepared free from carbonate by a method described by Jorissen and Filippo.



Solubility of Potassium Hydroxide

The solubility of potassium hydroxide has been studied by Pickering, some of his results being given in the appended table:

Temperature, °C-40-30-20-100102030405060708090100110120140140
Grams of KOH per 100 grams of water61.282.487.992.399.2106.1112.7122.2136.9143.9150157.9163.4177.7187.3201.2214.4235.5281.6


The density of the solution saturated at 15° C. is 1.536.

Chemical Properties of Potassium Hydroxide

Potassium hydroxide or caustic potash is the type of a strong base. In aqueous solution it is very extensively dissociated into its ions, and the properties of hydroxidion are, therefore, very strongly developed. Even in very dilute solution it colours litmus blue and phenolphthalein red. Somewhat stronger solutions have a soapy feeling, because they dissolve the skin of the fingers and convert it into a slimy mass; they exhibit a similar solvent action on fats, horn, hair, and like animal substances. Acids of all kinds are neutralised, i.e. converted into potassium salts, and neutral salts containing other metals are mostly decomposed in such a way that potassium salts are formed and the metals are deposited as hydroxides.

Since the last reaction is largely made use of in analysis and for of caustic potash is added to the solution of a salt the metal of which forms a sparingly soluble hydroxide, this hydroxide will be precipitated, because so much hydroxidion is introduced into the solution by means of the potash that the solubility product of the hydroxide in question is greatly exceeded. Since, now, the hydroxides of almost all the metals except the alkali metals are less soluble than potassium hydroxide, their salts are all decomposed in the above manner by potash solution.

Thus, solutions of zinc salts give a white precipitate of zinc hydroxide with caustic potash; solutions of nickel salts, a green; and copper salts a blue precipitate of hydroxide. Ammonium salts on being heated after the addition of caustic potash, evolve ammonia gas, which can be detected by its smell and by the fumes which it gives with hydrochloric acid, because the ammonion undergoes transformation with the hydroxyl to form water and ammonia.

All these reactions are clue to hydroxidion and not to kalion, for the same reactions are given when the latter is replaced by natrion or the ion of any other alkali metal. What has just been said is, therefore, not a description of caustic potash in particular, but of the strongly dissociated hydroxides in general.

Chemical properties the potassium derivative

In chemical properties the potassium derivative resembles sodium hydroxide, the aqueous solution being a strong base, a solution containing 6.7 gram-molecules of the hydroxide per litre having the maximum OH'-concentration. The hydroxide readily absorbs ozone, the product being possibly the heptoxide, K2O7.

Three hydrates have been isolated, the monohydrate, dihydrate, and tetrahydrate, melting respectively at 143° C., 35.5° C., and -32.7° C., the transition-point of the first and second being 32.5° C., and of the second and third -33° C.

The action of aqueous solutions of potassium hydroxide on sulphur is similar to that of sodium hydroxide or of concentrated ammonium hydroxide.
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