Titration equimolar mixture-based

Fig. 3.6.3. The dependence of E vs initial molality of base-titrant 2NaOH (m -) at the potentiometric titration of Pb2+ (0.051 mol kg-1) in the molten KC1 — NaCl equimolar mixture at 700 °C (1), and the corresponding differential titration curve (2). The points in the titration curve are numbered according to the data in Table 3.6.1.

Fig. 3.7.18. Potentiometric titration curve of Mg2+ in the molten CaCl2-NaCl equimolar mixture at 575 °C (m = 0.107 mol kg-1). The abscissa axis is the ratio of the initial molality of the base-titrant to that of the metal cation (by Castrillejo et al. [178]).

The titration of a mixture ofp-nitrophenol (pfQ = 7.0) and m-nitrophenol pK = 8.3) can be followed spectrophotometrically. Neither acid absorbs at a wavelength of 545 nm, but their respective conjugate bases do absorb at this wavelength. The m-nitrophenolate ion has a greater absorbance than an equimolar solution of the p-nitrophenolate ion. Sketch the spectrophotometric titration curve for a 50.00-mL mixture consisting of 0.0500 M p-nitrophenol and 0.0500 M m-nitrophenol with 0.100 M NaOH, and compare the curve with the expected potentiometric titration curves. 

This region of the titration shows clearly the buffering action of a mixture of a weak acid with its conjugate base. At the half-equivalence point V = VJ2, [CH3COOH]o = [CH3COO ]o, which corresponds to an equimolar buffer at this point pH - pK. On either side of this point the pH rises relatively slowly as the NaOH solution is added. 

In contrast, germanium oxide was found to be appreciably soluble in the molten equimolar KCl-NaCl mixture and its solutions show weak acidic properties. Its acid-base titration using NaOH as a titrant results in the appearance of a small pO drop at the equivalence point ( 1 pO unit), which corresponds to the ligand number value —0.5. This allows us to conclude that the acid-base titration runs in one step, and the final product is di-germanate ion, Gc202... 

It has recently been observed31 that the completely reduced base form of polyaniline, (leucoemeraldine), spontaneously reduces, and is itself oxidized, when its solution in NMP is mixed with an NMP solution of the completely oxidized base form of polyaniline, (pernigraniline). This reaction may be studied by "titrating" a solution of the leucoemeraldine with a solution of pernigraniline and by following the course of the reaction by the changes in the electronic spectrum of the reaction mixture. When equimolar solutions of the reactants are mixed this redox reaction is found to approach equilibrium after 20 hours at room temperature, to produce the emeraldine base, viz.,... 

---