Reduction of Bi(III) from highly concentrated perchloric acid

Abstract

In highly concentrated HClO₄ solutions (≥ 8 mol dm^-3) the reduction of Bi(III) at dropping mercury electrode is reversible due to the low concentration of free water molecules. The mechanism of reduction which includes the formation of an adion: Bi(OH₂)<img src='http://www.niscair.res.in/jinfo/equation124.gif' border=0> + Hg <img src='http://www.niscair.res.in/jinfo/doublearrow1.gif' border=0> ;Bi(OH₂)<img src='http://www.niscair.res.in/jinfo/equation123.gif' border=0> (Hg)_s + H₂O is proposed. Formation of the adion is prompted by the adsorption of the Cl^- ion at the mercury surface: Bi(OH₂)<img src='http://www.niscair.res.in/jinfo/equation122.gif' border=0> + Hg <img src='http://www.niscair.res.in/jinfo/doublearrow1.gif' border=0> Bi(OH₂)<img src='http://www.niscair.res.in/jinfo/equation123.gif' border=0>(Hg)_s + CI<img src='http://www.niscair.res.in/jinfo/equation125.gif' border=0>(Hg)_s. The highest coordination number of Bi³⁺for the Cl^- anion is 6.