Silver Chlor-platinate, Ag2PtCl6, is obtained as a yellow precipitate by adding silver nitrate in excess to a cold solution of chlor-platinic acid. It is not quite pure, since it is slowly decomposed even by cold water, yielding silver chloride and a solution of platinum tetrachloride, which is dihydroxy-tetrachlor-platinic acid, PtCl4.2H2O or H2PtCl4(OH)2.
Upon filtering off the silver chloride and concentrating the solution over sulphuric acid, the pentahydrate, PtCl4.5H2O, crystallises out. On warming, however, with excess of silver nitrate, the silver salt of dihydroxy-tetrachlor-platinic acid is obtained, thus:
H2PtCl6 + 2AgNO3 = Ag2PtCl6 + 2HNO3
Ag2PtCl6 + 2H2O = 2AgCl + PtCl4
2H2O PtCl4.2H2O + 2AgNO3 = Ag2PtCl4(OH)2 + 2HNO3.
The heat of formation of silver chlor-platinate is as follows:
[PtCl4] + 2[AgCl] = [Ag2PtCl6] + 7.7 Cals. |