Acid-base titrations by stepwise additions of equal volumes of titrant with special reference to automatic titrations—I: Theory, discussion of the gran functions, the hofstee method and two proposed methods for calculating equivalence volumes

• Published in: Talanta (Oxford) 1976-11, Vol.23 (11), p.769-780
• Main Authors: Pehrsson, Lennart, Ingman, Folke, Johansson, Axel
• Format: Article
• Language: English
• ISSN: 0039-9140; 1873-3573
• DOI: 10.1016/0039-9140(76)80086-0

The range of acid stability constants over which the Gran functions are applicable in evaluating acid-base titrations at normal concentrations is studied and found to be quite narrow. Alternatively, the titrations can be evaluated by using non-approximative methods based upon an equation that is derived without making the simplifying assumptions leading to the Gran functions. One such method, introduced by Hofstee, is discussed and the results of a study of the effects of a systematic error in the pH-determinations upon the determination of the equivalence volume are given. Two other non-approximative methods for evaluating acid-base titrations that are particularly suitable for use in automatic titrations of many similar samples are also described. These methods yield correct values of the equivalence volume regardless of a possible systematic error in the pH-values and are particularly useful for titrations of moderately strong and very weak acids (stability constants up to 10 10–10 11 at 0.01 M concentration) where the Gran functions cannot be used.