potentiometric study of the interactions between Divalent Cations and Sodium Carboxylates in Aqueous Solution

摘要

The effect of the divalent cations Pb~(2+)and Ca~(2+) on the properties of carboxylates with different alkyl chain lengths (octanoate, decanoate and dodecanoate) in aqueous solution at 25 ℃, is evaluated using conductimetric and potentiometric data. Electrical conductance data show strong interaction for concentration ratio (carboxylate:divalent ion) up to around 2, suggesting an interaction stoichiometry of 2:1. With lead(Ⅱ), the concentration of free metal ion in solution has also been determined by using a selective electrode, and stability constants are proposed. In the presence of lead ions, the length of the surfactant alkyl chain has a direct influence in the hydrolysis process, followed by pH measurements, and this effect becomes more pronounced upon increasing the number of methylene groups of the carboxylate.