Thermodynamic Quantities for the Ionization Reactions of Buffers

250 GOLDBERG, KISHORE, AND LENNEN
Values adjusted to TÄ298.15 K and IÄ0
pK rH°/(kJ mol 1 ) Reference
Reaction „1…: H 3AsO 4ÄH ¿ ¿H 2AsO 4 À
2.5 07LUT
2.36 13WAS/STR
2.5 34BRI/JAC
2.22 2.2 53AGA/AGA
2.9 59CHU
2.19 3 59FLI/MIS
2.30 64SAL/SCH
7.8 64SEL/SUN
2.8 70SEC/IND
2.47 76TOS
2.5 88KHO/ROB
Reaction„2…: H 2AsO 4 À ÄH ¿ ¿HAsO4 2À
4.8 20BLA
7.2 27SKR/ZAH
7.5 28HUG
7.2 34BRI/JAC
6.98 0.15 53AGA/AGA
7.2 58MAD
6.3 59CHU
6.94 0.7 59FLI/MIS
1.7 64SEL/SUN
6.8 71BEE/LIN
6.17 73BEE/LAW
7.19 76TOS
7.09 76WAU
7.3 86GRE/TRA
Reaction„3…: HAsO 4 2À ÄH ¿ ¿AsO4 3À
9.9 20BLA
12.1 34BRI/JAC
11.48 0.9 59FLI/MIS
12.1 59CHU
15.9 64SEL/SUN
11.9 76TOS
Comments: We have adopted the calorimetric results of Sellers et al. 64SEL/SUN for all three reactions. The extrapolation to I0 is the major uncertainty
in the values of rH°. For the first and third reactions, there are serious discrepancies between the values of rH° calculated from the pKs determined at
several temperatures and the calorimetric values. The pK value for reaction 1 is based on an average of five sets of results 13WAS/STR, 53AGA/AGA,
59FLI/MIS, 64SAL/SCH, 76TOS where the extrapolation to I0 has either been done or is not too uncertain. For reaction 2, the pK is based on an average
of what appear to be the most reliable results 53AGA/AGA, 59FLI/MIS, 76TOS, 76WAU. For reaction 3, we have adopted a pK value based on an average
of all of the results with the exception of that of Blanc 20BLA which is discordant. A definitive study of these ionization reactions is needed.
J. Phys. Chem. Ref. Data, Vol. 31, No. 2, 2002