Pentachlor-hydroxy-platinic Acid, H₂PtCl₅(OH)

The nionohydrate of Pentachlor-hydroxy-platinic Acid, H₂PtCl₅(OH), namely, H₂PtCl₅(OH).H₂O, is obtained as a deliquescent residue on keeping crystals of hexachlor-platinic acid in a vacuum over caustic potash at 100° C. for three days:

H₂PtCl₆.6H₂O = H₂PtCl₅(OH).H₂O + HCl + 4H₂O.

It readily dissolves in water, yielding a yellow solution with an acid reaction, sufficiently powerful to decompose carbonates. With ammonia no precipitate is obtained, which property serves to distinguish this acid from hexachlor-platinic acid. With ammonium chloride or potassium chloride the corresponding hexaehlor-platinate is produced.

Titration with alkali, using phenolphthalein as indicator, shows that the acid is dibasic, and several salts have been prepared.