Hydrolytic equilibria of lead(II) at 100 °C in 3.6 mol kg–1 LiClO4

Abstract

An in situ method, which allows the generation, analysis and measurement of the free hydrogen-ion concentration of aqueous solutions at high temperature (100 °C), has been elaborated. It is based on the use of a galvanic cell without a liquid junction containing a glass electrode and of a cell where controlled external and/or internal electrolysis processes take place. The reliability of the method has been checked by carrying out coulometric acid–base titrations of standard dilute HClO₄ solutions in 3 mol dm^–3 LiClO₄ as ionic medium. The high accuracy so obtained has made it possible to study lead(II) hydrolysis at 100 °C. In the whole range of lead(II) concentration investigated (2 × 10^–3–0.1 m) the collected data (Z→ log h) can be explained by assuming the formation of a mononuclear [Pb(OH)]⁺(log β₁₁=–6.05 ± 0.01) and a tetranuclear species [Pb₄(OH)₄]⁴⁺(log β₄₄=–15.94 ± 0.03). An increase in temperature from 25 to 100 °C has the effect of increasing the acidic properties of lead(II) solutions and of decreasing the number of hydrolysed species.