Thermodynamics of hydrochloric acid in 1-propanol from e.m.f. measurements at 5 to 45 °C

The standard electromotive force of the cell: Pt | H₂ (g, 1 atm) | HCI (m) in 1 - propanol | AgCI | Ag. has been determined at nine temperatures ranging from 5 to 45 °C. The standard e.m.f. E° varied with Celsius temperature θ according to the equation: E ° / V = - 0.1200 - 15.874 × 10^{- 4} (θ / ° C - 25) - 6.529 (θ / ° C - 25)² . The activity coefficients of hydrochloric acid, the primary medium effect, and the thermodynamic functions ΔG°_t, ΔH°_t, and ΔS°_t for the transfer of HCl from water to pure 1-propanol have been determined from the e.m.f. measurements. The molality of the acid ranged from 0.006 to 0.099 mol kg^-1. A large positive value for the Gibbs free energy of transfer suggests that the affinity of 1-propanol for HCl is less than that of water. The electrostatic contribution toward the total Gibbs free energy of transfer was evaluated on the basis of Born's electrostatic model and hence the chemical effect has been obtained by subtracting the electrostatic free energy from the total Gibbs free energy. At 25 °C the solvent has a dielectric constant of 20.1.