Thermodynamic Quantities for the Ionization Reactions of Buffers

260 GOLDBERG, KISHORE, AND LENNEN
Values from literature—Continued
pK rH°/(kJ mol 1 ) T/K I Methods and comments Reference
9.1013 318.15 0
9.0766 323.15 0
9.0537 328.15 0
9.0310 333.15 0
14.3 293.15 ? Calorimetry. The value given here was calculated from the
experimental results of Harries et al. 68HAR together with the
value of rH° for the ionization of water at T298.15 K calculated
from Eq. 9 of Olofsson and Hepler 75OLO/HEP. Harries
68HAR did not specify the ionic strength.
9.242 13.5 298.15 0 Electrochemical cell with liquid junction. Mesmer and Baes
9.088 323.15 0
8.998 348.15 0
8.952 373.15 0
8.938 398.15 0
8.950 423.15 0
8.983 448.15 0
9.041 473.15 0
9.135 498.15 0
9.291 523.15 0
9.550 548.15 0
9.970 573.15 0
72MES/BAE obtained pK values for the reaction
BOH 3OH BOH) 4 at temperatures over the range 323
T/K563. The values given here were calculated from the
equation given by Mesmer and Baes 72MES/BAE in their abstract
and by using thermodynamic data from Olofsson and Hepler
75OLO/HEP see their Eq. 9b for the ionization of water.
Mesmer and Baes 72MES/BAE also give data leading to
rC p /(J K 1 mol 1 )197 at T298.15 K.
68HAR
72MES/BAE
16.3 298.15 2.0 M Calorimetry 73BAR/RED
Values adjusted to TÄ298.15 K and IÄ0
pK rH°/(kJ mol 1 ) rC p /(J K 1 mol 1 ) Reference
9.236 14.0 200 34OWE2
9.237 13.2 307 35OWE
9.237 13.4 301 43OWE/KIN
9.234 14.2 200 44MAN/DEL
14.3 68HAR
9.242 13.5 197 72MES/BAE
16.3 73BAR/RED
Comments: We have selected the value pK9.237 based on the results of Owen et al. 34OWE2, 35OWE, 43OWE/KIN. The differences between this
selected value and the results of Manov et al. 44MAN/DEL and of Mesmer and Baes 72MES/BAE, while small, are slightly larger than one would like
to see for this fundamental system. We adopt rH°/(kJ mol 1 )13.8 based on the work of the above studies excepting the discordant value from Barres
et al. 73BAR/RED. The difficulties inherent in obtaining an accurate value of rC p from the second derivative of pK values determined as a function of
temperature are apparent from the above results. We have adopted the value rC p /(J K 1 mol 1 )240. While the apparent molar heat capacity of H3BO 3
has been determined 95HNE/MAJ, the ion H 2BO 3 has not been the subject of a similar study. Carefully done calorimetric measurements as a function of
temperature would also be useful in firmly establishing the value of rH° and of rC p . Additional studies, performed under a variety of conditions, are cited
by Martell et al. 2001MAR/SMI and by Pettit and Powell 2000PET/POW.
TABLE 7.16. CABS
Other names 4-cyclohexylamino-1-butanesulfonic acid; CAS No. 161308-34-5
Empirical formula C 10H 21NO 3S
Molecular weight 235.34
Ionization Reaction
Structure:
J. Phys. Chem. Ref. Data, Vol. 31, No. 2, 2002
HL H L , where HLC 10H 21NO 3S
There do not appear to be any thermodynamic data in the literature for the ionization of CABS.