By: Braibanti, Antonio; Bruschi, Claudio; Fisicaro, Emilia; Pasquali, Marzia Homogeneous sets of data from strong acid-strong base potentiometric titrns. in aq. soln. at various const. ionic strengths were analyzed by statistical criteria to see whether the error distribution matches that for the equil. consts. detd. by competitive potentiometric methods using the glass electrode. The titrn. curve can be defined when the estd. equivalence vol. (VEM), with std. deviation (s.d.) σ(VEM), the std. potential E0, with s.d. σ(E0), and the operational ionic product of water Kw* in mV), with s.d. σ(Kw*) [or σ(Ew*)] are known. A special computer program, BEATRIX, was written which optimizes the values of VEM, E0 and Kw* by linearization of the titrn. curve as a Gran plot. Anal. of variance applied to a set of 11 titrns. in 1.0M NaCl medium at 298 K demonstrated that the value of VEM belong to a normal population of points corresponding to individual potential/vol. data-pairs (Ei·,vi) of any titrn., whereas the values of pKw* (or of Ew*) belong to a normal population with members corresponding to individual titrns., which is also the case for the equil. consts. The intertitrn. variation is attributable to the electrochem. component of the system and appears as signal noise distributed over the titrns. The correction for junction-potentials, introduced in a further stage of the program by optimization in a Nernst equation, increases the noise, i.e., σ(pKw*). This correction should therefore be avoided whenever it causes an increase of σ(pKw*). The influence of the ionic medium was examd. by processing data from acid-base titrns. in 0.1M KCl and 0.5M KNO3 media. The titrns. in KCl medium showed the same behavior as those in NaCl medium, but with an s.d. for pKw* that was smaller and close to the expected instrumental noise, whereas the titrns. in nitrate medium had a high noise level and even the detn. of VEM was less certain. Procedures are also proposed for obtaining ref. sets of data and checking the conformity of the solns. and app. to the chosen ref.
|Tipologia ministeriale:||Articolo su rivista|
|Appare nelle tipologie:||1.1 Articolo su rivista|