Chemical elements
  Platinum
    Isotopes
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    Production
    Application
    Physical Properties
    Chemical Properties
      Platinum Difluoride
      Platinum Tetrafluoride
      Platinum Dichloride
      Tetrachlor~platinous Acid
      Tetrachlor-platinites
      Potassium Tetrachlor-platinite
      Trichlor-hydroxy-platinous Acid
      Silver Trichlor-hydroxy-platinite
      Platinum Trichloride
      Caesium Pentachlor-platinite
      Platinum Tetrachloride
      Ammonium Chlor-platinate
      Caesium Chlor-platinate
      Potassium Chlor-platinate
      Rubidium Chlor-platinate
      Silver Chlor-platinate
      Sodium Chlor-platinate
      Pentachlor-hydroxy-platinic Acid
      Barium Pentachlor-hydroxy-platinate
      Silver Pentachlor hydroxy-platinate
      Tetrachlor-dihydroxy-platinic Acid
      Dichlor-tetrahydroxy-platinic Acid
      Monochlor-pentahydroxy-platinic Acid
      Platinum Dibromide
      Brom platinous Acid
      Brom-platinic Acid
      Platinum Di-iodide
      Platinum Tetra-iodide
      Iodo-platinic Acid
      Ammonium Iodoplatinate
      Potassium Iodo-platinate
      Sodium Iodo-platinate
      Tetra-iodo-dihydroxy-platinic Acid
      Platinum Monoxide
      Triplatinum Tetroxide
      Platinum Sesquioxide
      Platinum Dioxide
      Hexahydroxy-platinic Acid
      Platinum Trioxide
      Platinum Monosulphide
      Platinum Sesquisulphide
      Platinum Disulphide
      Potassium Thio-platinate
      Platinum Oxysulphide
      Platinum Disulphate
      Platinum Monoselenide
      Platinum Triselenide
      Platinum Subtelluride
      Platinum Monotelluride
      Platinum Ditelluride
      Ammonium Platinonitrite
      Potassium Platinonitrite
      Silver Platinonitrite
      Platinum Subphosphide
      Platinum Monophosphide
      Platinum Diphosphide
      Platinum Arsenide
      Platinum Di-antimonide
      Monocarbonyl Platinum Dichloride
      Sesquicarbonyl Platinum Dichloride
      Dicarbonyl Platinum Dichloride
      Diphosgene Platinum Dichloride
      Carbonyl Platinum Dibromide
      Monocarbonyl Platinum Di-iodide
      Carbonyl Platinum Monoxide
      Carbonyl Platinum Monosulphide
      Carbonyl Platinum Thiocyanate
      Platinous Cyanide
      Cyanoplatinous Acid
      Platinocyanides
      Aluminium Platinocyanide
      Ammonium Platinocyanide
      Barium Platinocyanide
      Calcium Platinocyanide
      Cerium Platinocyanide
      Copper Platinocyanide
      Hydrazine Platinocyanide
      Hydroxylamine Platinocyanide
      Indium Platinocyanide
      Lead Platinocyanide
      Magnesium Platinocyanide
      Potassium Platinocyanide
      Radium Barium Platinocyanide
      Rubidium Platinocyanide
      Sodium Platinocyanide
      Sodium Potassium Platinocyanide
      Strontium Platinocyanide
      Uranyl Platinocyanide
      Dichlorcyanoplatinic Acid
      Cyanoplatinic Acid
      Lithium Platinicyanide
      Potassium Platinicyanide
      Silver Platinicyanide
      Potassium Thiocyanoplatinite
      Ammonium Thiocyanoplatinate
      Potassium Thiocyanoplatinate
      Potassium Selenocyanoplatinate
      Platinum Subsilicide
      Platinum Monosilicide
    Catalyst
    PDB 1a2e-2bho
    PDB 2ch8-3un9
    PDB 3vdk-5bna

Brom-platinic Acid, H2PtBr6






Brom-platinic Acid, H2PtBr6, was first obtained by Balard in a more or less pure condition by acting on platinum with a mixture of nitric and hydrobromic acids.

A more satisfactory method consists in dissolving platinum sponge in hydrobromic acid saturated with bromine. This may be effected in a sealed glass tube at 180° C., but that is not necessary. If the platinum sponge is simply boiled for a short time with an excess of bromine and hydrobromic acid in a flask with a reflux condenser, the whole is dissolved, yielding a solution of brom-platinic acid.

Gutbier prepared pure brom-platinic acid by repeatedly evaporating the pure chloride with concentrated hydrobromic acid on the water-bath and then treating it similarly three or four times with hydrobromic acid containing bromine. The residue, on being taken up with dilute hydrobromic acid, yields a deep carmine-red solution.

Brom-platinic acid crystallises in red, monoclinic prisms, containing 9 molecules of water, thus: H2PtBr6.9H2O. The crystals are deliquescent and readily soluble in water, alcohol, and ether. When heated in air to 180° C. they melt, water and hydrogen bromide being evolved, platinic bromide constituting the residue.

The heat of formation is as follows:

[Pt] + 2Br2 + 2HBr. Aq. = H2PtBr6.Aq. + 60.7 Cals.

Brom-platinic acid possesses a strongly acid character, decomposing carbonates and uniting with bases generally, to form salts known as:


Brom-platinates, M2PtBr6

These salts are isomorphous with the chlor-platinates already described, and which they resemble in their general chemical reactions. The alkali salts are best known, and are readily prepared by addition of a solution of the alkali bromide to one of brom-platinic acid, and crystallising the precipitated complex from dilute hydrobromic acid.

The solubilities of the alkali brom-platinates in water and dilute hydrobromic acid decrease with increasing atomic weight of the alkali metal. The solutions obtained are red in colour, but turn yellow on dilution with water. Hydrazine hydrate decomposes them with ease, metallic platinum being deposited and nitrogen evolved.

Numerous brom-platinates of organic bases have been prepared and described, but to deal with these is beyond the scope of this work. The more important inorganic brom-platinates are as follow:

Ammonium Brom-platinate, (NH4)2PtBr6

Ammonium Brom-platinate, (NH4)2PtBr6, crystallises in cubic octahedra, which are dark brown in colour and isomorphous with the corresponding potassium salt.

When heated, ammonium brom-platinate decomposes, partly according to the equation

3(NH4)2PtBr6 = 3Pt + 16HBr + 2NH4Br + 2N2,

and partly

(NH4)2PtBr6 = Pt + 2NH4Br + 2Br2.

By thorough drying of the salt, however, the quantity of bromine liberated is reduced.

The density of the salt is 4.265. It dissolves in water to a deep orange-red solution, which, when saturated at 20° C., contains 0.59 grams of (NH4)2PtBr6 per 100 grams of solution.

Caesium Brom-platinate, Cs2PtBr6

Caesium Brom-platinate, Cs2PtBr6, crystallises in reddish yellow octahedra.

Potassium Brom-platinate, K2PtBr6

Potassium Brom-platinate, K2PtBr6, results as dark brown octahedra, from which it is difficult to remove all traces of water. The crystals are not very soluble, a solution saturated at the ordinary temperature containing 2.02 per cent, of its weight of the salt. At 100° C. the salt dissolves in 10 times its weight of water. The density of the crystals is 4.658.

The heat of formation is:

[Pt] + 2(Br2) + 2KBr.Aq. = K2PtBr6.Aq. + 59.3 Cals.

The heat of solution is:

[K2PtBr6] + Aq. = K2PtBr6. Aq. - 12.2 Cals.

Rubidium Brom-platinate, Rb2PtBr6

Rubidium Brom-platinate, Rb2PtBr6, yields reddish yellow octahedra. The salt retains traces of moisture most obstinately.

Sodium Brom-platinate, Na2PtBr6

Sodium Brom-platinate, Na2PtBr6.6H2O, yields deep red, triclinic prisms, isomorphous with those of sodium chlor-platinate hexahydrate. The salt is readily soluble in water, stable in air, and has a density of 3.323.

Tetrabrom-dihydroxy-platinic Acid, H2PtBr4(OH)2

Platinum tetrabromide is only slightly soluble in water, yielding a reddish brown solution containing the dihydroxy acid. With silver nitrate the acid solution yields a dark brown precipitate of the silver salt, Ag2PtBr4(OH)2.

In an analogous manner salts of lead, PbPtBr4(OH)2.Pb(OH)2; thallium, Tl2PtBr4(OH)2; and mercury, HgPtBr4(OH)2, have been prepared, whilst electric conductivity measurements indicate that the sodium salt, Na2PtBr4(OH)2, can exist in solution.
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