The Ionization Constants of Nitrobenzoic and Benzoic Acids in Water-Ethanol Mixture at 25 °C from Conductance Measurements

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Abstract
Molar conductances of dilute solutions of 2-, 3-, 4-nitrobenzoic and benzoic acids are reported at 25°C in ethanol–water (EtOH–H2O) mixtures over composition range from 0 to 70 wt% of ethanol. The ionization constants and limiting molar conductances of these acids have been computed from the data using Fuoss 1978 conductance equation. Solvent effect on the ionization of acids in EtOH–H2O mixtures has been discussed in terms of free energy of transfer of respective anions of the acids from H2O to EtOH–H2O mixtures. It is found that the order of ionization of these acids in EtOH–H2O system is 2-nitrobenzoic acid>3-nitrobenzoic acid \simeq4-nitrobenzoic acid>benzoic acid.