Chemical elements
  Cadmium
    Isotopes
    Energy
    Production
    Application
    Physical Properties
    Chemical Properties
      Cadmium Fluoride
      Cadmium Chloride
      Cadmium Bromide
      Cadmium Iodide
      Cadmium Chlorate
      Cadmium Perchlorate
      Cadmium Bromate
      Cadmium Iodate
      Cadmium Periodate
      Cadmium Suboxide
      Cadmium Oxide
      Cadmium Hydroxide
      Cadmic Hydroxide
      Cadmium Peroxide
      Cadmium Sulphide
      Cadmium Sulphite
      Cadmium Sulphate
      Cadmium Thiosulphate
      Cadmium Dithionate
      Cadmium Selenide
      Cadmium Selenites
      Cadmium Selenate
      Cadmium Telluride
      Cadmium Tellurite
      Cadmium Tellurate
      Cadmium Chromite
      Cadmium Chromate
      Cadmium Dichromate
      Cadmium Molybdate
      Cadmium Tungstate
      Cadmium Nitride
      Cadmium Azide
      Cadmium Amide
      Cadmium Nitrite
      Cadmium Nitrate
      Cadmium Phosphide
      Cadmium Hypophosphite
      Cadmium Orthophosphate
      Cadmium Pyrophosphate
      Cadmium Thiophosphates
      Cadmium Arsenide
      Cadmium Arsenite
      Cadmium Arsenates
      Cadmium Metantimonate
      Cadmium Carbonate
      Cadmium Thiocarbonate
      Cadmium Cyanide
      Cadmium Silicate
      Cadmium Borates
    PDB 1a4k-1exq
    PDB 1f48-1ihu
    PDB 1ii0-1mhu
    PDB 1mms-1qvg
    PDB 1qy0-1wb6
    PDB 1wje-2avp
    PDB 2b3p-2j6e
    PDB 2jdz-2x05
    PDB 2x09-3ccj
    PDB 3ccl-3ggf
    PDB 3h1u-3p5v
    PDB 3p5w-8ice

Cadmium Iodide, CdI2






The anhydrous salt of Cadmium Iodide, CdI2, has been prepared by heating equivalent quantities of cadmium and iodine in an evacuated tube. It also crystallises, in transparent hexagonal crystals, from solutions obtained by (a) the action of iodine upon cadmium under water; (b) the action of aqueous hydriodic acid upon cadmium carbonate or metallic cadmium, or a mixture of these two, or cadmium oxide; (c) interaction between potassium iodide and cadmium sulphate.

It has been prepared pure by dissolving cadmium carbonate in hydriodic acid, evaporating to dryness with excess of the acid, and heating in a current of hydrogen iodide.

Determinations of its density have varied greatly and Clarke and Kebler inferred that the salt existed in both an α-form and a β-form of lower density that was brownish and gradually transformed into the α-variety at 50° C. According to Snell, the so-called β-cadmium iodide, of low density, obtained by crystallising the salt from its solution in hydriodic acid, contained hydrogen iodide and water, and he concluded that there is no valid evidence for a cadmium iodide of lower density than 5.6. Cohen and Moesveld affirm that between ordinary temperatures and its melting-point (about 400° C.) cadmium iodide exists in a stable α-form of density 5.670 at 30°/4° C, and an unstable β-form of considerably less density. If this is so, the properties of cadmium iodide, as usually described, refer to a mixture of the two forms in unknown proportions.

Cadmium iodide is said to melt at 385° C. and boil at 708°-719° C. It is readily oxidised by nitrogen peroxide at ordinary temperatures and by oxygen when heated. It dissociates slightly when heated in nitrogen, and is incompletely reduced by heating in a current of hydrogen. Its heat of formation is 48.5 Cal.

The salt is very soluble in water - a solution saturated at 18° C. contains 46.02 per cent, of cadmium iodide - and no hydrates have been crystallised from its solutions. Its heat of solution is –9.60 Cal.

Aqueous solutions of cadmium iodide are somewhat strongly ionised.

The experimental data indicate the presence of complex ions, and, according to McBain, dilute solutions contain the ions Cd•• and I', and concentrated solutions the ions Cd•• and CdI'3.

Solubility curves Cd-halides
Solubility curves of the cadmium halides.
Cadmium iodide dissolves in alcohol, ether, and amyl alcohol. Its heats of solution in methyl, ethyl, and propyl alcohols are respectively 6.65, 4.31, and 2.66 Cal. Neither methylene iodide nor arsenic tribromide has a solvent action on it. Conductivity and osmotic data indicate that complex ions exist in its solutions in the alcohols.

The boiling-points of its solutions in quinoline indicate the formula CdI2.

Cd12I23 is analogous to Cd4Cl7, and is prepared in a similar manner.


Compounds of Cadmium Iodide with Ammonia

Cadmium iodide absorbs ammonia gas, at a gentle heat, to form the hexammoniate CdI2.6NH4. It is a white powder, decomposed by water, that loses its ammonia when heated. When a solution of the anhydrous salt in warm ammonia solution is cooled, colourless crystals of the di-ammoniate CdI2.2NH4 separate. They melt, on heating, with the loss of their ammonia, and are decomposed by water. When ammonia solution is added to a solution of cadmium iodide, the product is usually a mixture of this ammoniacal and a basic salt. By using dilute solutions the basic salt only is precipitated. The diammoniate can then be crystallised from the mother-liquor. By severely limiting the quantity of ammonia any formation of the ammoniacal salt is prevented. Some oxyiodides of cadmium have been described.

Cadmium Hydrogen Iodides

Dry cadmium iodide absorbs hydrogen iodide. It is also readily soluble in concentrated hydriodic acid solution. This solution, on cooling to - 25° C., deposits a crystalline precipitate which is probably an unstable acid cadmium iodide. Cryoscopic data indicate the presence of CdI2.2HI in the solution. Colourless needles of CdI2.HI.3H2O have been obtained by saturating a pasty mass of cadmium iodide and its saturated solution with hydrogen iodide and cooling to -4.7° C. They are only stable in contact with the mother-liquor or in an atmosphere of hydrogen iodide.

Double Iodides of Cadmium

The following salts have been prepared: 2NaI.CdI2.6H2O, 2NaI.2CdI2.5H2O; 2KI.CdI2, KI.CdI2.H2O, 2KI.CdI2.2H2O; CsI.CdI2.H2O, 2CsI.CdI2, 3CsI.CdI2; NH4I.CdI2H2O, NH4I.CdI2.H2O, 2NH4I.CdI2.2H2O; SrI3.CdI2.8H2O; BaI2.CdI2.5H2O; CdI2.3HgI2.

Cadmium iodide forms double salts with many iodides of substituted ammonium bases.
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