Conductometric Titration of Poliprotic Acids in non Aqueous Mixed Solvents. Effects of Temperature and Composition of the Solvent Mixture.

The effects of temperature and composltlon of the solvent mixtures on the shape and on the analytical recoveries of conductometric tltratlons of polyprotlc aclds were studled for the solvent system 2-methoxyethanol/ethane-1,2-diol operating at -10, 25, 50, and 75 °C. The experimental evidence indicates that the N- or chair-shape of the tltratlon curves depends on the solvent physicochemical propertles, on the temperature, and on the acld solute to be tltrated; in particular the Influence of the distance between the carboxylic groups Is discussed. Titrations performed In 2-methoxyethanoi are associated in general wlth N-shaped curves, which however turn to chalr-shaped as the temperature Increases. Ethane-1,2-diol always produces chair-shaped curves as a consequenceof its more dlssoclating ability toward the tltratlonformed adducts. The study of the tltrations of phthalic acld In some mixtures of the above solvents exhibited behaviors consistent wlth previous observations regarding the exlstence of a partlcuiar “limiting mlxture” whlch separates the solvent system under study Into two well-defined groups (0 Ix . ~< “~limiting mixture” and “limiting mixture”