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Browsing FC - DQ | Documentos por Auto-Depósito by Subject "Activity coefficients"
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- Activity coefficients in the evaluation of food preservativesPublication . Mendonça, António; Vaz, Margarida I. P. M.; Mendonça, DinaFood preservatives are used in very low concentrations. However, usually they are used in aqueous high ionic strength solutions. The Pitzer model allows activity coefficient determination in these cases. Without the knowledge of activity coefficients, activity or ‘correct concentration’ cannot be known. In this work, the activity coefficients of sodium chloride, potassium chloride and calcium chloride in pure solutions were calculated by the Debye H¨uckel theory and the Pitzer theory. The calculated values were compared with experimental values. Activity coefficients of pure sodium benzoate in aqueous mixed solutions with potassium chloride or calcium chloride were evaluated using the Pitzer model. The same evaluation can be done to more complex systems once all Pitzer parameters values for the ionic species are known.
- Activity coefficients of dipotassium phthalate and potassium hydrogen phthalate in water at 298.15KPublication . Mendonça, António; Juusola, Pekka M.Pitzer model parameters and modified Guggenheim equation parameters for dipotassium phthalate (K2PH) and potassium hydrogen phthalate (KHPh) were determined from cell potential difference (cpd) measurements on galvanic cells without liquid junction. Mean activity coefficients of these salts in water at 298.15 K were calculated by the Pitzer model and modified Guggenheim equations. The Pitzer parameters values obtained for K2Ph where: Beta 0(K2Ph)+steta(Cl,Ph) = 0.25 ± 0.01 mol−1 kg; Beta 1 (K2Ph)= 0.86 ± 0.08 mol−1 kg; C(K2Ph)= −0.010 ± 0.002 mol−2 kg2 and ΨK,Cl,Ph = 0.014 ± 0.005 mol−2 kg2. The Pitzer parameters values obtained for KHPh were: Beta0 (KHPh + steta(Cl,Ph)= 0.084 ± 0.013 mol−1 kg, = 0 mol−1 kg. The results were also compared to the values obtained from Pitzer parameters published in literature. The parameter values for the modified Guggenheim equations (bK,Ph = −0.041 mol−1 kg and bK,HPh = −0.020 mol−1 kg) obtained in this study were used in the mean activity coefficients calculations. The modified Guggenheim equation allows us to obtain similar mean activity coefficient values, as the Pitzer equation, up to 1.5 mol kg−1 ionic strength for K2Ph and 0.5 mol kg−1 for KHPh.
- Activity coefficients of sodium benzoate and potassium benzoate in water at 298.15 KPublication . Mendonça, António; Cardoso, Cristina M. P.; Juusola, Pekka M.Industrial additives, like sodium benzoate and potassium benzoate, are used in low concentrations in aqueous solutions. However, in general, the ionic strength of the aqueous media is high. The Pitzer model allows the determination of activity coefficients in aqueous media. In this work, Pitzer parameters for sodium benzoate were recalculated (β(0)=0.162 mol−1 kg and β(1)=0.38 mol−1 kg) and Pitzer parameters for potassium benzoate were determined (β(0)=0.157 mol−1 kg and β(1)=0.27 mol−1 kg) from cell potential difference (cpd) measurements on galvanic cells without liquid junction. From these values, activity coefficients of potassium benzoate in water and in aqueous potassium chloride solutions were calculated by the Pitzer model. The activity coefficients were also calculated by modified Guggenheim equations with parameters obtained in this work and the results of the two models were compared.
- Determination of Pitzer parameters for sodium benzoate at 298.15 KPublication . Mendonça, António; Vaz, Margarida; Ferra, Maria I.Sodium benzoate is a salt widely used in industry as preserver. Its activity coefficients in aqueous solutions can be estimated by Pitzer theory, once the necessary parameters are known. Electromotive force (emf) measurements on galvanic cells without liquid junction have been used for the determination o f mean activity coefficients of sodium chloride in the ternary system sodium chloride + sodium benzoate (NaB) + water. Pitzer theory has been applied to this system and those data enabled the evaluation of the specific parameters for sodium benzoate at 298.15 K by linear regression. The values obtained f o r / B(0) NaB and B(1) NaB parameters, respectively 0.177 kg mol-1 and 0.34 kg mol-1 are close to those published already for other carboxylic acid salts.
- Re-evaluation of the Activity Coefficients of Aqueous Hydrochloric Acid Solutions up to a Molality of 16.0 mol·kg−1 Using the Hückel and Pitzer Equations at Temperatures from 0 to 50 °CPublication . Partanen, Jaakko; Juusola, Pekka M.; Vahteristo, Kari P.; Mendonça, AntónioThe simple three-parameter Pitzer and extended Huckel equations were used for calculation of activity coefficients of aqueous hydrochloric acid at various temperatures from 0 to 50◦C up to a molality of 5.0mol·kg−1. A more complex H¨uckel equation was also used at these temperatures up to a HCl molality of 16 mol·kg−1. The literature data measured by Harned and Ehlers J. Am. Chem. Soc. 54, 1350–1357 (1932) and 55, 2179–2193 (1933) and by Åkerl¨of and Teare [J. Am. Chem. Soc. 59, 1855–1868 (1937)] on galvanic cells without a liquid junction were used in the parameter estimations for these equations. The latter data consist of sets of measurements in the temperature range 0 to 50 ◦C at intervals of 10 ◦C, and data at these temperatures were used in all of these estimations. It was observed that the estimated parameters follow very simple equations with respect to temperature. They are either constant or depend linearly on the temperature. The values for the activity coefficient parameters calculated by using these simple equations are recommended here. The suggested new parameter values were tested with all reliable cell potential and vapor pressure data available in literature for concentrated HCl solutions. New Harned cell data at 5, 15, 25, 35, and 45 ◦C up to a molality of 6.5mol·kg−1 are reported and were also used in the tests. The activity coefficients obtained from the new equations were compared to those calculated by using the Pitzer equations of Holmes et al. [J. Chem. Thermodyn. 19, 863–890 (1987)] and of Saluja et al. [Can. J. Chem. 64, 1328–1335 (1986)] at various temperatures, and by using the extended H¨uckel equation of Hamer and Wu [J. Phys. Chem. Ref. Data 1, 1047–1099 (1972)] at 25 ◦C.