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6968931 
Journal Article 
Re-evaluation of the First and Second Stoichiometric Dissociation Constants of Oxalic Acid at Temperatures from 0 to 60 A degrees C in Aqueous Oxalate Buffer Solutions with or without Sodium or Potassium Chloride 
Partanen, JI; Juusola, PM; Covington, AK 
2009 
Yes 
Journal of Solution Chemistry
ISSN: 0095-9782
EISSN: 1572-8927 
38 
11 
1385-1416 
WOS:000272159300003 
Equations were developed for the calculation of the first stoichiometric (molality scale) dissociation constant (K (m1)) of oxalic acid in buffer solutions containing oxalic acid, potassium hydrogen oxalate, and potassium chloride from the determined thermodynamic values of this dissociation constant (K (a1)) and the molalities of the components in the solutions. Similar equations were also developed for the second stoichiometric dissociation constant (K (m2)) of this acid in buffer solutions containing sodium or potassium hydrogen oxalate, oxalate and chloride. These equations apply at temperatures from 0 to 60 A degrees C up to ionic strengths of 1.0 mola <...kg(-1) and they have been based on single-ion activity coefficient equations of the Huckel type. For the equations for K (m1), the activity parameters of oxalate species and the K (a1) values were determined at various temperatures from the Harned cell data of a recent tetroxalate buffer paper (Juusola et al., J. Chem. Eng. Data 52:973-976, 2007). By using the resulting equations for K (m1), the activity parameters of oxalate species for K (m2) and the K (a2) values were then determined from the new Harned cell data and from those of Pinching and Bates (J. Res. Natl. Bur. Stand. (U.S.) 40:405-416, 1948) for solutions of sodium or potassium oxalates with NaCl or KCl. The resulting simple equations for calculation of K (m1) and K (m2) for oxalic acid were tested with all important thermodynamic data available in the literature for this purpose. The equations for ln (K (a1)) and ln (K (a2)) are of the form ln (K (a))=a+b(t/A degrees C)+c(t/A degrees C)(2). The coefficients for ln (K (a1)) are the following: a=-2.8737, b=0.000159, and c=-0.00009. The corresponding coefficients for ln (K (a2)) are -9.6563, -0.003059, and -0.000125, respectively. The new activity coefficient equations were used to evaluate the pH values of the tetroxalate buffer solution (i.e., of the 0.05 mola <...kg(-1) KH(3)C(4)O(8) solution) for comparison with the pH values recommended by IUPAC at temperatures from 0 to 60 A degrees C and to develop a new two-component oxalate pH buffer of 0.01 mola <...kg(-1) KHC(2)O(4)+0.05 mola <...kg(-1) Na(2)C(2)O(4) for which pH values are given from 0 to 60 A degrees C. Values of p(m (H)) calculated from these equations are tabulated for these buffers as well as for buffer solutions with KCl and KH(3)C(4)O(8) as the major component and minor component, respectively. Tables of p(m (H)) are also presented for 0.001 mola <...kg(-1) KHC(2)O(4)+0.005 mola <...kg(-1) Na(2)C(2)O(4) solutions in which KCl is the supporting electrolyte. 
Activity coefficients; Hydrogen electrode; Silver-silver chloride electrode; Oxalic acid; Dissociation constant; Critical evaluation; Debye-Huckel equation; pH buffer solutions