SPECTROPHOTOMETRIC DETERMINATION OF DISSOCIATION-CONSTANTS FOR PROPIONIC-ACID AND 2,5-DINITROPHENOL AT ELEVATED-TEMPERATURES

Using the temperature dependence of pK(a) for acetic acid, the pK(a) f or 2,5-dinitrophenol have been spectrophotometrically determined in ac etate buffer at elevated temperatures under the saturation vapor press ures. For 2,5-dinitrophenol pK(a) = -33.206 + 2106.7/T + 5.495lnT wher e T is in Kelvin. Similarly, pK(a) values of propionic acid were obtai ned at temperatures from 25 degrees C to 175 degrees C producing pK(a) = -43.703 + 2128.6/T + 7.2686lnT From this result, several thermodyna mic functions of propionic acid were calculated and compared with thos e obtained from emf measurement.