Thermodynamics of the dissociation of ammonium ion in seawater from 5 to 40°C

The dissociation constant of NH4+ and the associated thermodynamic functions ΔH° and ΔS° in synthetic seawaters of salinity 20.31, 35.00, and 44.55‰ have been determined by emf measurements of cells without liquid junction over the temperature range 5 to 40°C. Cells with hydrogen electrodes and silver-silver chloride electrodes, whose standard potentials in seawater media were determined in an earlier investigation, were used. At a given temperaturet (in °C), pKa varies linearly with the formal ionic strengthIf (uncorrected for ion pairing) according to pKa=pKaw+(0.1552−0.0003142t)If where pKaw is the pK in pure water. The medium effect of seawater on ΔH° amounts to less than 200 cal-mole−1 for a change inIf from 0 to 0.72 mole-kg−1, and ΔS° is less than 1 cal-°K−1-mole−1 in all of the media studied, as it is in water. The observed salt effect on pKa is in close agreement with values predicted from theories of ion-ion interactions.

[1]  R. Robinson,et al.  A note on the temperature variation of the ionisation constants of weak electrolytes , 1940 .

[2]  R. Bates,et al.  Acidic dissociation constant of ammonium ion at 0 to 50 C, and the base strength of ammonia , 1949 .

[3]  D. H. Everett,et al.  The thermodynamics of ionization of some fatty acids , 1952, Proceedings of the Royal Society of London. Series A. Mathematical and Physical Sciences.

[4]  N. W. Please.  Estimation of the variance of the data used in the calculation of dissociation constants. , 1954, The Biochemical journal.

[5]  R. A. Robinson,et al.  The vapour pressure and osmotic equivalence of sea water , 1954, Journal of the Marine Biological Association of the United Kingdom.

[6]  Standard Electrode Potential of the Silver, Silver Chloride Electrode , 1956 .

[7]  R. Bates,et al.  Thermodynamics of Solutions of Deuterium Chloride in Heavy Water from 5 to 50 , 1964 .

[8]  J. Gillette,et al.  Effect of ambient ammonia on blood ammonia and nitrogen excretion of rainbow trout (Salmo gairdneri). , 1968, Comparative biochemistry and physiology.

[9]  D. R. Kester,et al.  Effect of temperature and pressure on sulfate ion association in sea water , 1970 .

[10]  C. Culberson,et al.  Ionization of water in seawater , 1973 .

[11]  M. Whitfield,et al.  The Hydrolysis of Ammonium Ions in Sea Water-a Theoretical Study , 1974, Journal of the Marine Biological Association of the United Kingdom.

[12]  L. Hepler,et al.  Calorimetric Heats of Ionization of Aqueous Benzoic Acid from 5–100 °C and Derived Thermodynamic Quantities , 1974 .

[13]  L. Hepler,et al.  Thermodynamics of ionization of water over wide ranges of temperature and pressure , 1975 .

[14]  D. Ives,et al.  Derivation of thermodynamic functions of ionisation from acidic dissociation constants. The sigma plot method vis-à-vis polynomial regression procedures , 1976 .

[15]  K. H. Khoo,et al.  Determination of hydrogen ion concentrations in seawater from 5 to 40.degree.C: standard potentials at salinities from 20 to 45% , 1977 .