OSMOTIC PROPERTIES OF A CATION-EXCHANGE MEMBRANE - REFLECTION COEFFICIENTS OF A SOLUTE LARGER THAN 1 IN A SYSTEM WITH AQUEOUS MIXED ELECTROLYTE-SOLUTIONS

The reflection coefficient of HCl of a cation exchange membrane separa ting two homogeneous aqueous solutions containing HCl and NaCl [c'(HCl ) = 5 x 10(-3) c+, c''(HCl) = 2 x 10(-2) c+; c'(NaCl) = c''(NaCl) = c( NaCl): 0 less-than-or-equal-to c(NaCl) less-than-or-equal-to 0.5c+; c = 1 mol dm-3] exhibits a characteristic dependence on the concentrati on of NaCl. In the absence of NaCl the reflection coefficient sigma(HC l) has a value close to 1. With increasing values of the concentration of NaCl the value of the reflection coefficient sigma(HCl) increases and reaches a maximum value of about sigma(HCl) almost-equal-to 2.5 at [c(NaCl)/<c(HCl)>] almost-equal-to 5.0. Above this value the reflecti on coefficient sigma(HCl) decreases reaching values of sigma(HCl) almo st-equal-to 1 at values of [c(NaCl)/<c(HCl)>] almost-equal-to 45. This concentration dependence of sigma(HCl) is in qualitative agreement wi th recent theoretical predictions and independent calculations based o n the model of the membrane with narrow pores.