The apparent acid dissociation constant (Kc) of benzoic acid in water has been determined titrimetrically under ionic strength values between 0.00 and 0.50 mol•L −1 at a range of temperatures between 16˚C and 41˚C. The thermodynamic dissociation constant (as pKa) of benzoic acid was determined as 4.176 at 25˚C. No regular correlation between pKa of benzoic acid and the temperature in the range was used. The values of pKa are inversely proportional to temperatures between 16˚C and 30˚C. In this range of temperature, the values of thermodynamic quantities (o H ∆ , o S ∆ and o G ∆) for the dissociation process of benzoic acid in water were calculated by using Van't Hoff plot. For this case the dissociation was not favoured through entropy and enthalpy changes. The values of pKa are directly proportional to temperatures between 30˚C and 41˚C.

No abstract

No abstract

Different structures are proposed for the complexes formed from the interaction between the cationic cyanine dye 1, 1’-diethyl-2, 2’-carbocyanine chloride (Pinacyanol chloride) and the anionic surfactant sodium bis (2-ethylhexyl) sul- fosuccinate (Aerosol-OT) in ethanol-water solutions. UV/vis and electronic circular dichroism (CD) spectra provide tools to study the concentration and solvent dependence of this interaction. The aggregation spectra of the dye are dominated by a strongly blue-shifted, sharp and single visible band, which appears at concentrations much below the critical micelle concentration (cmc) of Aerosol-OT. Above the cmc, the spectra in pure aqueous solution indicate disso- ciation into monomer and dimer species, and the system becomes completely empty of chirality. Two different CD spectra with a distinct isosbestic point are observed for complexes with different surfactant to dye ratios. Both the addi- tion of ethanol (more than 7.5%) and increasing the temperature retards the metachromatic process between the dye and Aerosol-OT. By using the peakFit program, the two overlapping excitonic absorption bands together with the optically inactive absorption band for one spectrum (the most optimal one) at a specific Aerosol-OT concentration were sepa- rated

No abstract