Abstract
Titration studies of ammonium titanyl oxalate solutions with Pb(NO 3) 2 at an ionic strength of 0.5 M (NaClO 4) have shown that at pH > 1.5 precipitates are formed consisting of three compounds: PbTiO(C 2O 4) 2·4H 2O, PbC 2O 4 and Ti(OH) 4. The solubility product of lead titanyl oxalate (PTO) is (35 ± 2) times the solubility product of lead oxalate, i.e. log K PTO = −6.90 ± 0.03, when log K PO = −8.45 for lead oxalate as found by Klatt. The solubility product [Ti(OH) 2 2+][OH −] 2 was found to have the value log K TH = −30.5 ± 0.25. At low pH lead oxalate and titanium hydroxide dissolve. It is necessary to include a lead titanyl complex of unknown nature in calculation models for simulating equilibrium concentrations during titrations in order to explain the anomalously high dissolved lead(II) concentration. The solubility product calculated for PTO is not very sensitive to the different models. Lead and titanium contents of solutions equilibrated with solid PTO differed from the expected values based on the models for titrations. A satisfactory explanation for the low Ti(IV) and high Pb(II) concentrations can not yet be given.
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