Rapid acidification of solutions containing tungstate anions

Abstract

Potentiometric titration of H⁺ against tungstate, WO₄^2–, ions shows that the product formed in the first 0·01 s is not paratungstate A, HW₆O₂₁^5–, or any discrete ion intermediate between WO₄^2– and HW₆O₂₁^5–, but is a mixture of a number of ill-defined products. These may be colloidal hydrated tungsten(VI) oxides formed very rapidly in local regions of high acidity before complete mixing can occur. These are then rapidly (ca. 1 s) converted into HW₆O₂₁^5–. The pH was measured by an indicator–spectrophotometric technique using a stopped-flow spectrophotometer.