CITRATE COMPLEXES OF LEAD. PART II

The insoluble lead citrate compound, formed by the neat alisation of a citric acid solution contailiing. lead nitrate, is a dibasic acid. The compound is formed by the action of one of the carboxyl groups arid the hydroxyl group of the citric acid, and either a five- or a six- membered ring is formed. This insoluble compound dissolves when the \(p\)H is increased due to the formation of ,another complex (II) in which three co-ordinalion positions are occupied by a citrate ligand and, most probably, the fourth position by a molecule of water. This contains a free carboxyl group which ionises, followed by the ionisation of the water _.molecule, affording complex (III) and complex (IV) respectively. The latter ionisation takes place beyond g. The formation constants of the complexes (II) and (III) and dissociation constants of complex (H) to (III) and complex (III) to (IV) bare been determined.