On the Hydrolysis of Niobates in 3 M K(Cl) Medium.

Abstract

Potentiometric titrations were made at const. concn. of Nb (0.05, 0.10, and 0.14M) and const. ionic strength in the range of pOH 1.0-3.3. Acidification by adding NH4Cl to the solns. and removing NH3 with N gave reversible titrations from pOH 2.4-3.3, but turbidity and irreversibility were found at lower pOH. Only the hexanuclear species, H2Nb6O196-, was found, confirming the results of Jander and Ertel (CA 55, 2333a). The successive ionization consts. were pK1 = 10.88 ± 0.05 and pK2 = 13.8 ± 0.2. [on SciFinder(R)]