Complex formation in the ternary systems Ca II –H 4 SiO 4 –H 2 O and Mg II –H 4 SiO 4 –H 2 O

Calcium(II) and magnesium(II) complexes of partially deprotonated H4SiO4have been investigated at 25 °C in solutions of constant ClO4-molarity (1 M) by computer-controlled coulometric titration using a hydrogen electrode. The experimental data could be explained assuming the following equilibria. M2++ H3SiO4-→ MH3SiO4+; K1= [MH3SiO4+]/[M2+][H3SiO4-] and M2++ 2H3SiO4-→ M(H3SiO4)2; β2= [M(H3SiO4)2]/[M2+] [H3SiO4-]2or M2++ H2SiO42-→ MH2SiO4; χ1= [MH2SiO4]/[M2+][H2SiO42-]. For the individual equilibrium constants, the following values were obtained: Ca2+: log K1= 0.39 (±0.03); log β2= 2.89 (±0.07) (log χ1= 3.09) Mg2+: log K1= 0.64 (±0.06); log β2= 3.82 (±0.08) (log χ1= 4.17).

Complex formation in the ternary systems Ca II –H 4 SiO 4 –H 2 O and Mg II –H 4 SiO 4 –H 2 O Academic Article