Stability constants for the formation of lead chloride complexes as a function of temperature and ionic strength

The stability constants for the formation of lead (Pb2+) with chloridePb2++nCl-↔PbCln2-nβn(n=1,2,3)have been determined using a spectrophotometric method in NaClO4 solutions as a function of ionic strength (0–6 m) and temperature (15–45 °C). The results have been fitted to the equations:logβ1∗=logβ1+0.21I-8.61I0.5/(1+1.2I0.5)+1927.40[I0.5/(1+1.2I0.5)]/Tlogβ2∗=logβ2+0.32I-4.67I0.5(1+1.2I0.5)+594.54[I0.5/(1+1.2I0.5)]/Tlogβ3∗=logβ3+0.40I-2.68I0.5(1+1.2I0.5)-43.98[I0.5/(1+1.2I0.5)]/Twith standard errors of 0.05, 0.04 and 0.06, respectively. The thermodynamic values of log β1, log β2 and log β3 at 25.0 °C and the enthalpies of formation of PbCl+, PbCl20 and PbCl3- are in good agreement with literature values. We have combined our results with the earlier work of [Seward, T.M., 1984. The formation of lead (II) chloride complexes to 300 °C: a spectrophotometric study. Geochim. Cosmochim. Acta48, 121–134.] Seward (1984) to yield thermodynamic constants that are valid from 15 to 300 °C:logβ1=44.82+0.031T-21.21logTlogβ2=61.42+0.046T-29.51logTlogβ3=107.97+0.071T-51.46logTwith standard errors of 0.05, 0.08 and 0.10, respectively.