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DOI Prefix 10.20431 |
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Validity of the Criterion pKa = pH at the Half Equivalence Point for the Potentiometric Evaluation of the Ionization Constant of a Monoprotic Acid
Julia Martin1*, Laura Argeme-Caro2, Agustin G. Asuero2
2.Department of Analytical Chemistry, Faculty of Pharmacy, University of Seville, E-41012 Seville, Spain.
Citation : Julia Martin, Laura Argeme-Caro, Agustin G. Asuero, Validity of the Criterion pKa = pH at the Half Equivalence Point for the Potentiometric Evaluation of the Ionization Constant of a Monoprotic Acid International Journal of Advanced Research in Chemical Science 2018, 5(12) : 6-15.
The aim of this paper is to draw attention to the conditions under which the potentiometric evaluation of the acidity constant of a monoprotic acid, HA, can be performed from the single half point titration curve. We may usually adopt the pH corresponding to this point, pHT=0.5, as the pKa value avoiding the need of using a rigorous method of calculation involving the entire V-pH titration data. The complete and approximate theoretical relationships that allow making effective that choice have been derived. A literature search have been carried out in order to gather a number of papers in which the criterion pKa= pH0.5 has been used. In spite of the frequency with which this criterion is applied, it is only valid in favourable cases. A number of practical cases are included for study.