The effects of temperature and composition of solvent mixtures on conductometric tltratbns have been lnvestlgated for the solvent system 2methoxyethand/ethane-l,2dloi. Good analytical results were obtained for a series of monocarboxylic aiiphatk and ammatk aclds and phenols by uslng 0.10 M N,N'-dlphenylguanMlne as standard titrant. Conductance titration curves, performed at -10, 25, 50, and 75 O C in the abovementioned pure solvents and in their four binary mixtures, are plesented and discussed. The peculiar behavlor of pick ackl in the lnvestlgated solvent system is emphasized in the discusslon.
The titrimetric determination of weak acids or bases inin which a ion-pair-formation step is followed by a dissociation equilibrium, is one of the most powerful tools in analytical chemistry because it can provide information unavailable by other techniques, such as about the formation of ion pairing or other ion aggregation phenomena at the various points of the titration ( I , 2). Ion pairiig can influence the reaction rates and the equilibria for many solute-solvent systems at low concentrations, and consequently, it is an important factor in selecting solvents and reagents for analytical purposes (3).Conductance measurements are particularly effective in the determination of ion-pair formation constants and ion mobilities and remain a very useful technique especially for acquiring information about nonaqueous solutions. Furthermore, if used for titrations, a careful selection of the solvent system makes possible a differentiation of single functions present either in different molecular units or in the same molecule.Alcohols have received good attention as solvents for acid-base determinations (1,2) but not many conductometric studies appeared in the past about alcoholic solvent mixtures, only in the last years are they becoming more common (3). In our previous works (4-7) studies were reported on the feasibility of conductometric titrations of monoprotic and diprotic acids, phenols, and aromatic nitroderivatives in 2-methoxyethanol (hereafter abbreviated Gliem) and ethane-1,2-diol (Gliet) as solvents, using N,"-diphenylguanidine (DPG) as base titrant dissolved in the above media. The choice of the two solvents was suggested by considering that they are good solvents for the titration of acidic compounds, that the most common organic acids are soluble enough to do excellent titrimetric work, and that they are completely miscible. DPG was chosen because it can be conveniently recrystallized, it is a stable standard material, quite soluble in nonaqueous media, and it has a high equivalent weight; furthermore, DPG shows a low conductance in the solvents used, as revealed by the curvature in a X vs c1I2 plot. The results indicated also the possibility of performing differential titrations of acid mixtures in cases where such determinations are very difficult, if not impossible, in aqueous solutions.
nonaqueous solvents of the typeThe subsequent developments of this research should aid in the investigation of the influenc...