Solubility inert electrolyte effect

If adding an inert electrolyte is undesirable, or if no swamping electrolyte is sufficiently inert or soluble, then the effects of migration can be lessened somewhat by performing the analysis at low field, for instance with an electrode having a very small potential. Such a practice is seldom useful, though, from considerations of mass transport (see below). 

The above terminology ( inert vs. specific ) was adopted for studies of the surface charging of colloids. Different experimental methods are used and different quantities are measurable for colloids than for the Hg electrode, but the model of an electrical double layer is analogous. Studies of pH-dependent surface charging of colloids are usually carried out in the presence of an inert electrolyte and an acid or base (used to adjust the pH) with an anion or cation in common with the inert electrolyte. Products of dissolution of the solid are also present in solution at low concentration (we are only interested in sparingly soluble solids), but are ignored in most studies. Sometimes, the concentration of dissolution products is measured, and very occasionally the concentration of dissolution products (which are water-soluble salts) is controlled by addition of these salts to the dispersion. The effect of addition of Al(iii) salt on the potential of alumina was studied in [35]. At the lEP, the solubility of Al species is low thus, the lEP was not very different from that in a 1-1 electrolyte. The solubility problem is discussed in more detail in Section 1.6. 

In Chapter 6 we defined the thermodynamic equilibrium constant written in terms of activities to account for the effects of inert electrolytes on equilibria. The presence of diverse salts will generally increase the solubility of precipitates due to the shielding of the dissociated ion species. (Their activity is decreased.) Consider the solubility of AgCl. The thermodynamic solubility product K p is... 

We may also explain this effect with the use of Le Chatelier s principle. As the ionic strength increases by the addition of an inert electrolyte such as (NH SC, the ions of the protein that are in solution attract one another less strongly, so that the equilibrium is shifted in the direction of increased solubility,... 

One matter of interest which can be understood in terms of this equation is the. effect of inert electrolytes on solubilities. An inert electrolyte is one which does not... 

Discussing interface inhibition one finds that the pure squeezing out effect (salting out effect), which may concentrate inhibiting neutral molecules at the metal electrolyte interface, will be rather rare. However, it is possible that the activity of ions or molecules taking place in the corrosion reaction is decreased simply by the accumulation of neutral molecules in the vicinity of the metal surface. Such substances could be alcohol, water soluble inert solids in general, or inert ions. 

Polyelectrolytes are most commonly studied as solutions in aqueous media as a consequence of their poor solubility in organic solvents. In order to minimize the effects of ionization in an aqueous media, evaluation of [77] is done in an aqueous solution of an inert 1 1 electrolyte as the solvent. In such solvents, poly electrolytes behave as if they were neutral polymers [32-34],... 

The electrolyte, added to enhance conductivity and to minimize double-layer and migration current effects, is chosen on the basis of solubility in a given solvent as well as inertness toward the electroactive substance and its electrolysis products. There are of course many choices of electrolyte for use in aqueous solution. The tetraalkylammonium salts are the most commonly used non-aqueous electrolytes. Tetrabutylammonium tetrafluoroborate (TBATFB) and tetrabutylammonium hexafluorophosphate (TBAHFP) are recommended by Fry and Britton, who note that TBAHFP in acetonitrile has a particularly large useful potential range of +3.4 to —2.9 V (vs. SCE). 

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