Note 483 — Chapter XII · THE COPPER AND SILVER GROUPS (Continued).—THE THEORY OF COMPLEX IONS

For instance, for arsenious acid we have

3 H⁺ + AsO₃³⁻ ⇄ H₃AsO₃ ⇄ As³⁺ + 3 HO⁻

and, therefore, [As³⁺] × [HO⁻]³ / ([AsO₃³⁻] × [HO⁺]³) = k₁. Since [H⁺] = k′_HOH / [HO⁻] (p. 176), we have further, [As³⁺] × [HO⁻]⁶ / [AsO₃³⁻] = k₂. And since we may derive the relation [HO⁻]² = k₃ × [O²⁻], by considering the primary and the secondary ionization of water (see pp. 246, 278), we have, finally, [As³⁺] × [O²⁻]³ / [AsO₃³⁻] = K. The constants for the primary and the secondary ionization of water are included in the value of K.