Potentiometric Study on the Interactions between Divalent Cations and Sodium Carboxylates in Aqueous Solution - Progress in Organic and Physical Chemistry: Structures and Mechanisms - page 26

The addition of sodium octanoate leads to an increasing electrical conductivity of the
resulting solution, which indicates the absence of carboxylate calcium(II) interactions,
or, if they exist they are so weak and cannot be detected by electrical conductivity. For
sodium decanoate, the electrical conductivity behavior is very similar to what occurs
in solutions for example, sodium dodecyl sulfate and trivalent ions [43]. That is, the
addition of decanoate to a solution containing Ca 2+ leads to an initial increase of solu-
tion electrical conductivity because there is no interaction between species in this zone,
however, for a molar ratio [C 9 COO í ]/[Ca 2+ ] around 1, the speci¿ c conductance tends to
stabilize, which can be interpreted either as a critical aggregation concentration or ion
pair formation, after this, the Ca 2+ species interact with the decanoate, until the stoichio-
metric a molar ratio of 2.0, the speci¿ c conductance increases again.

FIGURE 1 Effect of Ca 2+ 1 mM (a) and Pb 2+ 1 mM and (b), in the specific conductivity of sodium
octanoate (Ƒ, n = 7), sodium decanoate (ż, n = 9), and sodium dodecanoate (

Δ , n = 11) at 25ºC.