1987 年 3 巻 6 号 p. 515-519
A statistical end point error in the strong acid-strong base titration using the Gran′s plot method has been studied theoretically on the basis of an individual source of errors arising in the course of determination. Errors in potential reading of the electrode system and in temperature reading of the titration solution were evaluated by the standard deviation of the volume at the end point as a function of the mean titration fraction of the data points used for extrapolation. The deviation of the Nernstian slope from the theoretical value and the term of the constant potential E° participating in the Nernstian equation should also be taken into account during the extrapolation; otherwise, the titration error will become significant. On the other hand, a small change of the initial volume of the titration solution created no serious problem on the end point. The experiment of micro-titration of HCl sample with 0.01M NaOH solution using the Gran′s plot method resulted in a reproducibility of the end point with a relative standard deviation of 0.62%, when two data points were taken at 30% and 50% of the titration fraction for the extrapolation.
