Complex formation in the ternary systems CaII–H4SiO4–H2O and MgII–H4SiO4–H2O

Abstract

Calcium(II) and magnesium(II) complexes of partially deprotonated H₄SiO₄ have 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^–]² or M²⁺+ H₂SiO₄^2–⇆ MH₂SiO₄; χ₁=[MH₂SiO₄]/[M²⁺][H₂SiO₄^2–] 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)