The first hydrolysis constant of Eu3+ has been determined at 303 K and
4 M (NaCl) ionic strength. A solvent extraction method was used, the
extractant was dibenzoylmethane in benzene and diglycolate anion in th
e aqueous phase provided competitive complexation. The reaction and th
e value obtained for the constant were: Eu3+ + H2O = Eu(OH)2+ + H+ log
beta1,H = -6.33 +/- 0.09.