Abstract
In highly concentrated 
(>8M) and acidic 
(>7M) solutions the reduction of Bi(III) at a mercury electrode becomes fast and reversible. The redox kinetics depends on the electrolyte concentration and only indirectly on the water activity. It is proposed that the cations of the supporting electrolyte participate in the partial dehydration process which follows the first charge‐transfer step. Hydration numbers of Bi3+ are 8.2 in 
and 6.9 in 
solutions.