THERMAL-DIFFUSION OF WEAK ELECTROLYTES - DETERMINATION OF NORMAL CARBOXYLIC-ACIDS IN AQUEOUS-SOLUTION

A new model is developed for determination of the Soret coefficient an d the enthalpy of transport for weak(pK similar to 4-5) 1:1 type elect rolytes in aqueous solutions. In the model the effects of both the the rmal diffusion and the shift of the dissociation equilibrium with temp erature and concentration are taken into account. The Soret coefficien ts of normal carboxylic acids - and also those of the ionic and molecu lar species separately - were calculated from the single ionic enthalp y of transport of the acidic anion. The results of calculations show t hat the differences between the enthalpies of transport of the ionic a nd molecular species are nearly identical with the enthalpies of disso ciation. Furthermore, the values of the Soret coefficients increase li nearly with the logarithm of the carbon number of the acid.