Physical Chemistry of Aqueous Systems: Meeting the Needs of Industry

ISBN Print: 978-1-56700-034-4

ISBN Online: 978-1-56700-445-8

HIGH TEMPERATURE pH MEASUREMENTS IN DILUTE AQUEOUS AMMONIA SOLUTIONS

DOI: 10.1615/ICPWS-1994.560
pages 441-448

Resumo

By employing an yttria-stabilized zirconia (YSZ) sensor, a hydrogen-platinum pH electrode, and an external pressure balanced reference electrode (EPBRE), experimental investigations of dilute aqueous ammonia solutions (0.4, 0.8, 1.2 ppm) at temperatures from 150°C to 300°C have been pursued. When employing EPBRE, the thermal liquid junction potential (TLJP) problem, which is a characteristic of this type of electrode, must be considered and an appropriate experimental and theoretical treatment of the problem has to be provided. Thermodynamics of non­isothermal cells (thermocells) is considered and applied, in order to derive pH values from the experimentally obtained potentials. Comparison with theoretically calculated pH values derived using the SUPCRT92 data base is presented. The estimated error of the measurements is found to be around ±0.1 pH units, which mainly appears due to a lack of our knowledge on the transport numbers ti and the Eastman entropies of transport S*i at temperatures higher then 100°C.