282
1. Grenthe
In the experiments, we measure the concentration of free or non-complex bound
Cu 2 + with the electrode. It is highly desirable that the activity coefficient for this species is constant throughout the experiment. Using the SIT single ion activity coefficient for Cu 2 +, we have:
logyc 2+ =-0.5100Z c
2 2+
.Ji .JI+C(Cu2+,CI04")mclO +c(Cu2+,CnmCI
U
U
1 + 1.5 I
4
From this equation, we can see that the activity coefficient of Cu 2 + will not be constant throughout the experiment. The interaction coefficients are c(Cu 2 +, CIO:!) = 0.32
and c(Cu 2 +, Cn '" 0.15. Hence, a replacement of 25% of a 3.5 molal NaCI04 ionic medium with NaCI will result in a change of 10glO YCu2+ equal to 0.14, which is not negligible. We could have studied the same system with a chloride electrode. In this case, it
would have been advantageous to keep the sodium ion concentration constant, because
the activity coefficients of a particular ion are mainly influenced by the ions of opposite charge. The example illustrates some of the problems encountered when interpreting equilibrium analytical data when large changes have been made in the ionic medium. An attempt to use the SIT method to interpret data in a mixed ionic medium is
described in Grenthe and Lagerman (1993). A more detailed discussion of ionic medium effects with several different examples is given in Grenthe et al. (1997).
References
Bodliinder G, Storbeck 0 (1902a) Z Anorg Chern 31:1
Bodliinder G, Storbeck 0 (1902b) Z Anorg Chern 31:458
Bodlander G, Fittig R (1902) Z Physik Chern Leipzig 39:597
Bodliinder G, Eberlin W (1904) Z Anorg Chern 39:197
BfllInsted IN (1922) J Am Chern Soc 44:877
Debye P, Hiickel E (1923) Physik Z 24:185
Euler H von (1903a) Ber 36:1854
Euler H von (1903b) Ber 36:2878
Euler H von (1903c) Ber 36:3400
Farkas I, Banyai I, Szabo Z, Wahlgren U, Grenthe I (2000) Inorg Chern 39:799
Grenthe I, Lagerman B (1993) Radiochim Acta 61:169
Grenthe I, Spahiu K, Plyasunov A (1997) Estimation of medium effects on thermodynamic data. In:
Grenthe I, Puigdomenech I (eds) Modelling in aquatic chemistry. Nuclear Energy Agency, OECD, Paris
Grossman H (1905) Z Anorg Chern 43=356
Guggenheim EA (1935) Philos Mag 19:588
Helgeson HC, Kirkham DH, Flowers GC (1981) Am J Sci 281:1249
Millero FJ (1983) Geochim Cosmochim Acta 47:2121
Moll H, Denneke MA, Ialilehvand F, Sandstrom M, Grenthe I (1999) Inorg Chern 38:1795
Pitzer KS (1973) J Phys Chern 77:268
Pitzer KS (1991) Ion interaction approach: Theory and data correlation. In: Pitzer KS (ed) Activity coefficients in electrolyte solutions, 2nd edn. CRC Press, Boca Raton, FL, pp 75-153
Pitzer KS, Brewer L (1961) Revision of Lewis and Randall's thermodynamics. McGraw-Hill, New York
Plyasunov A, Fanghanel T, Grenthe I (1998) Acta Chern Scand 52:250
Rossotti FIC, Rossotti H (1961) The determination of stability constants. McGraw-Hill, New York
Russel B (1959) A history of western philosophy, 12th edn. Simon and Schuster
Scatchard G (1959) The interpretation of activity and osmotic coefficients. In: Hamer WI (ed) The structure of electrolytic solutions.
Scatchard G (1976) Equilibrium in solution: Surface and colloid chemistry. Harvard University Press,
Cambridge, MA
Szabo Z, Aas W, Grenthe I (1997) Inorg Chern 36:5369
1. Grenthe
In the experiments, we measure the concentration of free or non-complex bound
Cu 2 + with the electrode. It is highly desirable that the activity coefficient for this species is constant throughout the experiment. Using the SIT single ion activity coefficient for Cu 2 +, we have:
logyc 2+ =-0.5100Z c
2 2+
.Ji .JI+C(Cu2+,CI04")mclO +c(Cu2+,CnmCI
U
U
1 + 1.5 I
4
From this equation, we can see that the activity coefficient of Cu 2 + will not be constant throughout the experiment. The interaction coefficients are c(Cu 2 +, CIO:!) = 0.32
and c(Cu 2 +, Cn '" 0.15. Hence, a replacement of 25% of a 3.5 molal NaCI04 ionic medium with NaCI will result in a change of 10glO YCu2+ equal to 0.14, which is not negligible. We could have studied the same system with a chloride electrode. In this case, it
would have been advantageous to keep the sodium ion concentration constant, because
the activity coefficients of a particular ion are mainly influenced by the ions of opposite charge. The example illustrates some of the problems encountered when interpreting equilibrium analytical data when large changes have been made in the ionic medium. An attempt to use the SIT method to interpret data in a mixed ionic medium is
described in Grenthe and Lagerman (1993). A more detailed discussion of ionic medium effects with several different examples is given in Grenthe et al. (1997).
References
Bodliinder G, Storbeck 0 (1902a) Z Anorg Chern 31:1
Bodliinder G, Storbeck 0 (1902b) Z Anorg Chern 31:458
Bodlander G, Fittig R (1902) Z Physik Chern Leipzig 39:597
Bodliinder G, Eberlin W (1904) Z Anorg Chern 39:197
BfllInsted IN (1922) J Am Chern Soc 44:877
Debye P, Hiickel E (1923) Physik Z 24:185
Euler H von (1903a) Ber 36:1854
Euler H von (1903b) Ber 36:2878
Euler H von (1903c) Ber 36:3400
Farkas I, Banyai I, Szabo Z, Wahlgren U, Grenthe I (2000) Inorg Chern 39:799
Grenthe I, Lagerman B (1993) Radiochim Acta 61:169
Grenthe I, Spahiu K, Plyasunov A (1997) Estimation of medium effects on thermodynamic data. In:
Grenthe I, Puigdomenech I (eds) Modelling in aquatic chemistry. Nuclear Energy Agency, OECD, Paris
Grossman H (1905) Z Anorg Chern 43=356
Guggenheim EA (1935) Philos Mag 19:588
Helgeson HC, Kirkham DH, Flowers GC (1981) Am J Sci 281:1249
Millero FJ (1983) Geochim Cosmochim Acta 47:2121
Moll H, Denneke MA, Ialilehvand F, Sandstrom M, Grenthe I (1999) Inorg Chern 38:1795
Pitzer KS (1973) J Phys Chern 77:268
Pitzer KS (1991) Ion interaction approach: Theory and data correlation. In: Pitzer KS (ed) Activity coefficients in electrolyte solutions, 2nd edn. CRC Press, Boca Raton, FL, pp 75-153
Pitzer KS, Brewer L (1961) Revision of Lewis and Randall's thermodynamics. McGraw-Hill, New York
Plyasunov A, Fanghanel T, Grenthe I (1998) Acta Chern Scand 52:250
Rossotti FIC, Rossotti H (1961) The determination of stability constants. McGraw-Hill, New York
Russel B (1959) A history of western philosophy, 12th edn. Simon and Schuster
Scatchard G (1959) The interpretation of activity and osmotic coefficients. In: Hamer WI (ed) The structure of electrolytic solutions.
Scatchard G (1976) Equilibrium in solution: Surface and colloid chemistry. Harvard University Press,
Cambridge, MA
Szabo Z, Aas W, Grenthe I (1997) Inorg Chern 36:5369