Beryllium(II) hydrolysis in 3.0 mol dm–3perchlorate

Abstract

The complex-formation equilibria in the system BeII–H2O have been studied at 25 °C by means of e.m.f. methods, using a coulometric titration technique, in 3.0 mol dm–3(Na)ClO4 solutions. The ranges of total beryllium(II) concentration and acidity were 80 B 1 mmol dm–3 and 2 ⩽–log h⩽ 6.2, respectively. Over the whole concentration range studied the data could be explained by assuming the equilibria (i)–(v). Previously reported information on beryllium(II) hydrolysis is 2Be2++ H2O ⇌[Be2(OH)]3++ H+ log β21=–3.23 ± 0.05 (i), 3Be2++ 3H2O ⇌[Be3(OH)3]3++ 3H+ log β33=–8.656 ± 0.002 (ii), 5Be2++ 6H2O ⇌[Be5(OH)6]4++ 6H+ log β56=–18.81 ± 0.03 (iii), 6Be2++ 8H2O ⇌[Be6(OH)8]4++ 8H+ log β68=–26.70 ± 0.05 (iv), Be2++ 2H2O ⇌ Be(OH)2+ 2H+ log β12=–11.09 ± 0.04 (v) reviewed and an attempt is made to correlate the data in different ionic media by using the Bronsted–Guggenheim–Scatchard specific ion interaction theory. The values of the equilibrium constants at infinite dilution derived from this approach are log β210=–3.47 ± 0.05, log β330=–8.86 ± 0.05, log560=–19.5 ± 0.1, and log β680=–26.3 ± 0.1. Tentative structures for the polynuclear hydroxo complexes are proposed and discussed. The solubility product of α-Be(OH)2(s) has been re-evaluated by using literature data and the hydrolysis constants of this study, at I= 0, log Kso=–6.87 ± 0.05.