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

Abstract

The complex-formation equilibria in the system Be^II–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 Brønsted–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 K_so=–6.87 ± 0.05.