Doctor of Philosophy
Department of Chemistry
Brown, Paul Leslie, Studies on the hydrolysis of metal ions, Doctor of Philosophy thesis, Department of Chemistry, University of Wollongong, 1984. http://ro.uow.edu.au/theses/1179
The potentiometric titration technique has been used to study the hydrolytic properties of six metal ions. Indium(III), thorium(IV), scandium(III), beryllium(II), and aluminium(III) were studied at 25°C and magnesium(II) was investigated at higher temperatures from 60° to 200°C.
Data analysis of the experiments performed at 25°C using a modified version of the MINIQUAD 75 program indicated the likely presence of the following species and formation constants: Indium(III): In(OH)2+ -4 .53(0.008), In(OH)2 + -9.34(0.02), and In2(OH)2 4+ -5 .48(0.007); Thorium(IV): Th(OH)3+ -2.98(0.007), Th4(OH)12 4+ -30.55(0.03), and Th6(OH)15 -34.41(0.03); Scandium(III): Sc(OH)2+ -4.840(0.008), Sc2(OH)2 4+ -6.096(0.004), and Sc3(OH)5 4+ -17.567(0.006); Beryllium(II): Be(0H)2 -11.320(0.008), Be2(OH)3+ -2.955(0.007), and Be3(0H)3+ -8.804(0.002); Aluminium(III): Al(OH)2+ -5.27(0.005), Al(0H)2 + -10.88(0.02), and Al3(OH)4 5+ -13.31(0.01). Data analysis of the high temperature experiments using the ORGLS program indicated the presence of Mg(OH)2(solid) as the sole product. The following results were obtained at varying temperatures and ionic strengths: 60°, 0.10, -15.29(0.02); 100°, 0.10, -13.45(0.02); 150°, 0.10, -11.62(0.007); 200°, 0.10, -10.21(0.01); 60°, 1.00, -15.52(0.01); 100°, 1.00, -13.64(0.02); 150°, 1.00, -11.88(0.006), 200°, 1.00, -10.44(0.01). The standard deviations of the formation constants have been given in parentheses for all species.
These results together with previous literature results for other metal ions have been analysed with the aim of rationalising the hydrolytic behaviour of the ions in terms of a common, theoretical basis. A correlation between the formation constants of the hydrolytic species formed and the charge, ionic radius, and electronic structure of the hydrolysing metal ion was found and the following equation for predicting the formation constant of the species Mp(0H)q (ignoring charges) has been developed.
-log βpq = [(p-1)int1 - q(int2)] + [(p-l)slp1 - q(slp2)] x [g1(z/r2 + g2)]
In the equation, z is the charge, r the ionic radius, int1 and slp1 , and int2 and slp2, are the least squares intercept and slope values of linear equations for the M(0H) and polymeric Mp(0H)q species, respectively, and g1 and g2 are functions dependent only upon the charge and electronic structure of the metal ion.
The results also suggested that a systematic testing mechanism for hydrolysis schemes could be developed. A subroutine was written for interfacing with the MINIQUAD program, which used a cluster search technique for this purpose.
Experimental design is discussed in detail. It is shown that the acquisition of a very large amount of very precise data in the appropriate concentration ranges (if experimentally accessible) is mandatory if meaningful results are to be obtained.