Abstract
The dissociation constant of NH +4 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), pK a varies linearly with the formal ionic strengthI f (uncorrected for ion pairing) according to pK a=pK wa +(0.1552−0.0003142t)I f where pK wa is the pK in pure water. The medium effect of seawater on ΔH° amounts to less than 200 cal-mole−1 for a change inI f 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 pK a is in close agreement with values predicted from theories of ion-ion interactions.
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Khoo, K.H., Culberson, C.H. & Bates, R.G. Thermodynamics of the dissociation of ammonium ion in seawater from 5 to 40°C. J Solution Chem 6, 281–290 (1977). https://doi.org/10.1007/BF00645459
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DOI: https://doi.org/10.1007/BF00645459