Hydrolytic behavior of oxovanadium(IV) ions.

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The hydrolysis of VO2+ was investigated in 0.1 M LiClO4 by potentiometric, conductometric and turbidimetric measurements. The following values of the equilibrium constants were obtained: β11=[VOOH+] [H+]⁄[VO2+]=9.0×10−6 M (M=mol dm−3); β22=[(VO)2(OH)22+][H+]2⁄[VO2+]2=1.9×10−7 M. The solubility product of VO(OH)2 given by Kspl=[VO2+][OH−]2 was found to be 6.6×10−23 M3 from the pH values at which precipitation occurs. Only one species with a stoichiometric ratio VO/OH=2.5 is present in basic solutions in the pH range 9–12. The solubility product of VO(OH)2 given by Ksp2=[H+][(VO)2(OH)5−] is logKsp2=−11.1. A less soluble salt Na(VO)2(OH)5 or NaHV2O5 was isolated from strongly basic solutions. Measurements of Na+ concentration at which the solid phase first appears give logKsp3=−3.74 as its solubility product, Ksp3=[Na+][(VO)2(OH)5−].
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