Apparent molar volumes and heat capacities of aqueous trifluoromethanesulfonic acid and its sodium salt from 283 to 328 K

Apparent molar heat capacities C-p,C-phi and volumes V-phi of aqueous trifluoromethanesulfonic (triflic) acid, HCF3SO3 (aq.) were determined with a Picker flow microcalorimeter and vibrating-tube densimeter at temperatures from 283 to 328 K and molalities from 0.05 to 9.5 mol-kg(-1). Values of V-phi and C-p,C-phi display a maximum near 0.8 mol-kg(-1) V-phi also displays a shallow minimum at similar to5 mol-kg(-1),while C-p,C-phi continues to decrease smoothly up to the limit of our measurements at 9.5 mol-kg(-1). We attribute this behavior to ion-ion interaction between triflate and the hydrated proton to form the aqueous complex H2n+1 O-n(+) CF3SO3-(aq.), n = 5. Standard partial molar properties C-p(o) and V-o are consistent with results obtained from NaCF3SO3 (aq.) and yield values for the triflate anion CF3SO3-(aq.). over this range.