Spectrophotometric determination of the acid dissociation constants for cacodylic acid and p-Nitrophenol at elevated temperatures

Using 2.5-dinitrophenol as an optical indicator, the pKa of cacodylic acid were spectrophotometrically determined at elevated temperatures under saturation vapor pressures. The result is pKa = -26.41 + 1296/T + 4.973 InT whereT is in Kelvin. In a similar way, the pKa ofp-nitrophenol were obtained up to 200‡C giving pKa = -24.82 + 2135/T + 4.353 InT From these results, several thermodynamic functions of cacodylic acid andp- nitrophenol were calculated.