Determination of Activity Coefficients of HBr in Aqueous Surfactant Solutions

Mean ionic activity coefficients of HBr in aqueous solutions of decyltrimethylammonium bromide (DTAB) and of sodium dodecylsulfate (SDS) have been calculated from EMF measurements of the cell: $${\rm{Pt;}}{{\rm{H}}_{\rm{2}}}\left( {{\rm{g}},1{\rm{atm}}} \right)|{\rm{HBr}}\left( {{{\rm{m}}_{{\rm{HBr}}}}} \right),{\rm{SURFACTANT}}\left( {\rm{m}} \right)|{\rm{AgBr;Ag}}$$ at temperatures ranging from 5° to 55°C. The concentration of DTAB was varied from 0.01 to 0.2 molal at fixed values of the concentration of HBr (0.002, 0.02, and 0.1 molal). Similar measurements were made for SDS (0.0015 to 0.05 molal) in 0.02 m HBr at temperatures ranging from 20° to 55°C. The dependence of the activity coefficient of HBr on the concentration of surfactant is compared with that calculated from a model which was developed previously for surfactant- electrolyte-water solutions.