Chemical elements
    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
      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 iodide, KI

The Potassium iodide, KI, is obtained by neutralizing the carbonate with hydriodic acid, and also by the interaction of potassium hydroxide and iodine, the iodate simultaneously produced being converted into iodide by heat or by the action of a reducer such as carbon:

6KOH + 3I2 = 5KI + KIO3 + 3H2O.

It is manufactured by the action of iron-filings on iodine in presence of water, the soluble iodide Fe3I8 formed being decomposed by potassium hydroxide, a process accompanied by precipitation of the oxide Fe3O4 and formation of a solution of potassium iodide. The salt crystallizes on concentration of the aqueous solution. It can also be prepared from the ashes of seaweed, and from the iodate present in Chile saltpetre.

Potassium iodide forms crystals belonging to the cubic system, melting at 677.3° C., 680° C., 684.1° C., 705° C., or 722.7° C. Its density is given by various investigators as 3.079, 3.043 at 24.3° C., and 3.115 at 25° C. The specific heat is given as 0.0766, and 0.0819 between 20° and 99° C. The heat of formation from the solid elements is 80.1 Cal.

The molecular electric conductivity of potassium iodide between 691.5° and 814° C. is given by the formula

μt = 85.41 + 0.1564(t - 700).

The salt dissolves in water to form a neutral solution, readily decomposed by atmospheric oxygen and carbon dioxide with separation of iodine.

Solubility of Potassium iodide in water

Temperature. °C.-100102030405060708090100110120
Solubility of KI in 100 gr of water115.1127.5136.0144152160168176184192200208215223

The boiling-point of a solution in contact with excess of the salt is 118.4° C., and the liquid contains 222.6 grams of dissolved salt per 100 grams of water.

At 25° C. 100 grams of ethyl alcohol dissolve 2.16 grams of potassium iodide.

Potassium iodide finds application in medicine. The chief impurities present in the " pure " commercial product are iodate, carbonate, and chloride of potassium.

On heating potassium iodide with ammonium bromide in a long narrow tube of hard glass, iodine is liberated. By the aid of this test one-tenth of a milligram of the iodide can be detected.

Various polyiodides of potassium have been mentioned as formed by addition of iodine to solutions of potassium iodide in water and in organic solvents. There seems to be much uncertainty as to whether they are true poly-derivatives or only mixtures of potassium iodide and iodine, but Foote and Chalker state that the compounds KI3 and KI7 have a definite existence.

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