Thermodynamic Quantities for the Ionization Reactions of Buffers

246 GOLDBERG, KISHORE, AND LENNEN
Values from literature
pK rH°/(kJ mol 1 ) T/K I Methods and comments Reference
52.5 298.15 Calorimetry. Vanderzee and King 72VAN/KIN later applied
dilution corrections to Pitzer’s 37PIT result and obtained rH°
3.35 kJ mol 1 for the reaction (NH 3H 2ONH 4 OH ). This
value when combined with rH° for the ionization of H 2O(1)
75OLO/HEP leads to rH°52.5 for the reaction
(NH 4 H NH3). Pitzer’s 37PIT original, uncorrected result led
to rH°/(kJ mol 1 52.2 kJ mol 1 .
9.867 278.15 0 Electrochemical cell with liquid junction. The value of rH° given
9.529 288.15 0
9.215 51.7 298.15 0
8.923 308.15 0
8.645 318.15 0
here was calculated from pKs measured at several temperatures. The
value rC p /(J K 1 mol 1 )3 was also calculated from the
temperature dependency of their 38EVE/WYN reported pKs.
Everett and Landsman 54EVE/LAN later stated that these results
were in error due to the presence of carbonate in the hydroxide
solutions used to prepare the buffer.
10.0813 273.15 0 Electrochemical cell—no liquid junction. The value of rH° given
9.9040 278.15 0
9.7306 283.15 0
9.5641 288.15 0
9.4002 293.15 0
9.2449 52.24 298.15 0
9.0926 303.15 0
8.9466 308.15 0
8.8047 313.15 0
8.6700 318.15 0
8.5387 323.15 0
here was calculated from pKs measured at several temperatures. The
value rC p /(J K 1 mol 1 )5 was also calculated from the
temperature dependency of their 49BAT/PIN2 reported pKs.
10.081 273.15 0 Electrochemical cell—no liquid junction. This study used a
9.904 278.15 0
9.730 283.15 0
9.564 288.15 0
9.401 293.15 0
9.246 52.19 298.15 0
9.093 303.15 0
8.947 308.15 0
8.805 313.15 0
8.671 318.15 0
8.540 323.15 0
somewhat different methodology than that used by Bates and
Pinching 49BAT/PIN2 in their earlier work. The value of rH°
given here was calculated from pKs measured at several
temperatures. The value rC p /(J K 1 mol 1 )5 was also
calculated from the temperature dependency of their 50BAT/PIN
reported pKs
9.5537 288.15 0 Electrochemical cell with liquid junction. The pK values given here,
9.2378 51.9 298.15 0
8.9425 308.15 0
8.6683 318.15 0
and which pertain to a molality standard state, were calculated from
the pK values given by Everett and Landsman 54EVE/LAN and
which pertained to the molarity scale. The value of rH° given here
was calculated from the pKs measured at several temperatures. The
value rC p /(J K 1 mol 1 )24 was also calculated from the
37PIT
38EVE/WYN
49BAT/PIN2
50BAT/PIN
54EVE/LAN
52.59 298.15 0 temperature dependency of their 54EVE/LAN reported pKs. Calorimetry. 61TYS/MCC
9.29 52.01 298.15 0.1 M Potentiometric titration—glass electrode; calorimetry. 65PAO/STE
68VAS/KOC
52.15 298.15 0 Calorimetry. Values of rH° were determined for the temperature
range 291.15T/K313.15. Results were obtained at several ionic
strengths and extrapolated to I0. The value rC p /(J K 1 mol 1 )
7 atT298.15 was calculated from the temperature dependence
of the rH° values. In performing this calculation values of rH°
52.34 298.15 0
for the ionization of water were taken from Olofsson and Hepler
Calorimetry. 69CHR/IZA
50.12 ? ? Calorimetry. 71MAR/BER
51.99 298.15 0 Calorimetry. Vanderzee et al. 72VAN/KIN report rH° 3.828 kJ mol1 for the reaction (NH3H2ONH4 OH ) at T
298.15 K and I0. This value when combined with rH° for the
ionization of H2O(1) 75OLO/HEP leads
51.99 kJ mol
to rH° 1 72VAN/KIN
for the reaction (NH4 H NH3).
75OLO
51.92 298.15 0 Calorimetry. Values of rH° were determined for the temperature
range 278.15T/K418.15. The value rC p /(J K 1 mol 1 )11 at
T298.15 was calculated from the temperature dependence of the
J. Phys. Chem. Ref. Data, Vol. 31, No. 2, 2002
rH° values.
The result rC p /(J K 1 mol 1 )7 atT298.15 K was obtained by
direct heat capacity measurements.
81ALL/WOO