Equilibrium constants of ion exchange reactions between fatty acid monolayers and dissolved counterions

Equations for equilibrium constants of ion exchange between fatty acid monolayers and subsolution counterions are derived. The approach of Matsubara et al. [4], where the monolayer is considered as a two-dimensional regular mixture is employed, but the different molar volumes of its components are taken into account. Using the equations obtained theK_ex values are calculated on the basis of published data on the monolayer composition in the systems Cd²⁺/HArch, Ba²⁺/HArch, Ca²⁺/HSt, Pb²⁺/ HSt and Cu²⁺/HSt. The stability constants of the corresponding soaps formed in the monolayer are also obtained.