Potassium Chlor-platinate, K₂PtCl₆

Potassium Chlor-platinate, K₂PtCl₆, is most readily obtained by adding potassium chloride to an acidulated solution of platinum tetrachloride. It crystallises in cubic octahedra which are yellow in colour and but slightly soluble in water, and still less soluble in alcohol. The formation of this salt is therefore utilised in the quantitative estimation of potassium and platinum.

Its solubility in water at various temperatures is as follows:

Temperature ° C.	0	6.8	13.8	46.5	71	100
Grams K2PtCl6 in 100 grams H2O	0.724	0.873	0.927	1.776	3.018	5.23

The heat of formation of potassium chlor-platinate is:

[Pt] + 2(Cl₂) + 2KCl.Aq. = K₂PtCl₆.Aq. + 83.3 Cals.

When ignited, the salt decomposes, yielding a mixture of spongy platinum and potassium chloride. The reaction is not readily completed in air, but in a current of hydrogen the decomposition is quantitatively exact. The density of potassium chlor-platinate is 3.499.