Dissociation constant of aqueous trifluoroacetic acid by cryoscopy and conductivity

The dissociation constant of trifluoroacetic acid in aqueous solution has been determined at 25°C by electrical conductivity (0.65 mol-l^–1) and at 0°C by cryoscopy (1.05 mol-l^–1) and electrical conductivity (0.98 mol-l^–1). The good agreement between the values of the constant determined by cryoscopy and conductivity at 0°C lends confidence to the value at 25°C determined by electrical conductivity. The constant determined at 25°C is in reasonable agreement with values determined by differential refractometry (0.92 mol-l^–1) and from acidity function data (0.80 mol-l^–1) reported by other workers. This work renews confidence in the electrical conductivity method for determining dissociation constants of moderately strong acids.