The hydrolysis of lead(II). A potentiometric and enthalpimetric study

The hydrolysis of lead(II) has been investigated by potentiometric titrations (ionic medium 1.0M NaClO(4) and 1.0M KNO(3)) and enthalpimetric titrations (ionic medium 1.0M NaClO(4)) at 25 degrees . The reaction model that gave the best fit to the data for 1.0M NaClO(4) comprised the following five ions: Pb(OH)(+), Pb(3)(OH)(2+)(4), Pb(3)(OH)(+)(5), Pb(4)(OH)(4+)(4) and Pb(6)(OH)(4+)(8). The formation constants, and enthalpy changes (kJ/mol) for these species, defined according to equation (1), have the values log beta(11) = -7.8, DeltaH(0)(11) = 24; log beta(34) = -22.69, DeltaH(0)(34) = 112; log beta(35) = -30.8, DeltaH(0)(35) = 146; log beta(44) = -19.58, DeltaH(0)(44) = 86; log beta(68) = -42.43, DeltaH(0)(68) = 215. Equilibrium constants determined in nitrate medium show good agreement with those pertaining to perchlorate medium if complexation of lead(II) with nitrate is taken into account.