Apparent molar volumes and apparent molar heat capacities of aqueous phenol and sodium phenolate at temperatures from 278.15 to 393.15 K and at the pressure 0.35 MPa

Abstract

Apparent molar volumes V φ and apparent molar heat capacities C p, φ have been determined for aqueous solutions of phenol (C 6H 5OH) and its sodium salt (C 6H 5ONa) at temperatures T from 278.15 to 393.15 K, at the pressure 0.35 MPa, and at molalities m from 0.025 to 0.50 mol· kg −1 . We used a vibrating tube densimeter (DMA 512P, Anton PAAR, Austria) to determine the densities and volumetric properties, and a twin fixed-cell, power-compensation, differential-output, temperature-scanning calorimeter (NanoDSC 6100, Calorimetry Sciences Corporation, American Fork, UT, USA) to obtain the heat capacities. Infinite dilution partial molar volumes V 2 0 and heat capacities C 0 p,2 were obtained over the range of temperatures by extrapolation to m=0 mol· kg −1 on the fitted surfaces ( V φ , T, m) and ( C p, φ , T, m). Our results were combined with values of V φ and C p, φ from the literature for NaCl(aq), HCl(aq), and NaOH(aq) to obtain (Δ r V m, T, m) and (Δ r C p,m , T, m) for the proton dissociation reaction of C 6H 5OH(aq). Surfaces representing (Δ r H m, T, m), (p Q a, T, m), and (Δ rS m, T, m) where created by integration of our (Δ r C p,m , T, m) surface using values for (Δ r H m, m) and ( pQ a, m) at T=298.15 K from the literature as integration constants.