A comparison of the base decomposition of 12-tungstophosphate(3–), 12-tungstosilicate(4–), 12-tungstoborate(5–), and dihydrogendodeca-tungstate(6–)

Abstract

The reaction of [PW₁₂O₄₀]^3–, [BW₁₂O₄₀]^5–, and [H₂W₁₂O₄₀]^6–(1.5 × 10^–5 mol dm^–3) with excess of hydroxrde ion at an ionic strength of 1.0 mol dm^–3 MCI (M = K, Na, or Li). to form [WO₄]^2–, phosphate, and borate, has been studied. The rate, and in some instances the mechanism, of the reactions is dependent on the cation chosen to maintain the ionic strength. For simple second-order reactions the rate decreases in the order [SiW₁₂O₄₀]^4– > [BW₁₂O₄₀]^–5∼[H₂W₁₂O₄₀]^6–. Other mechanisms involve a pre-equilibrium with partially hydrolysed species. Rate constants are in the order K⁺ > Na⁺ > Li⁺. Measurements in mixed K⁺–Na⁺ media show that [BW₁₂O₄₀]^5– preferentially forms ion pairs with the sodium ion.