| Popis: |
The electrometric titration method, using a glass electrode and silver, silver bromide electrode in a cell without a liquid junction, has been used to determine the dissociation constants of eight substituted phenols, i.e. 2,3-(NO2)2-, Cl5-, 2,5-(NO2)2-, 2,4,6-Cl2-, 2,5-Cl2-, 4-NO2-, 2-NO2- and 3,5-Cl2-, in four acetone + water mixtures at 0.2, 0.4, 0.6 and 0.8 mole fraction, at 298 K at a constant ionic strength of 0.02 mol dm–3.An activity correction derived from Debye–Huckel theory was applied to the thermodynamic pKa values obtained. The pKa of the acids was found to vary linearly with the mole fraction of acetone over the range 0.2–0.80.The variations in pKa with the solvent composition are discussed in terms of the free energies of transfer of phenols, phenoxide anions and the proton from water to the acetone + water mixtures. |
