Electrolyte electrolytic solutions

This chapter will include equilibria at non-polarizable interfaces for a metal or semiconductor phase-electrolyte system (a galvanic cell in the broadest sense) and for two electrolytes (the solid electrolyte-electrolyte solution interface, or that between two immiscible electrolyte solutions). 

Finally, consider a metal (ar)-solid electrolyte ( )-electrolyte solution (y) system where the solid electrolyte and the electrolyte solution contain a common anion A- and the metal and the solid electrolyte contain a common cation B+ (for simplicity, only univalent ions are considered). The potential difference between phase a (metal) and phase y (solution) is... 

The electrical double layer has also been investigated at the interface between two immiscible electrolyte solutions and at the solid electrolyte-electrolyte solution interface. Under certain conditions, the interface between two immiscible electrolyte solutions (ITIES) has the properties of an ideally polarized interphase. The dissolved electrolyte must have the following properties ... 

A solute may be present as ions or as molecules. We can identify the form of the solute by noting whether the solution conducts an electric current. Because a current is a flow of electric charge, only solutions that contain ions conduct electricity. There is such a tiny concentration of ions in pure water (about 10-7 m) that water alone does not conduct electricity. A substance that dissolves to give a solution that conducts electricity is called an electrolyte. Electrolyte solutions (solutions of electrolytes), which conduct electricity because they contain ions, include aqueous solutions of ionic compounds, such as sodium chloride and potassium nitrate. The ions are not formed when an ionic solid dissolves they exist as separate ions in the solid but become free to move apart in the presence of water (Fig. 1.1). Acids also are electrolytes. Unlike salts, they are molecular compounds in the pure state but form ions when they dissolve. One example is hydrogen chloride, which exists as gaseous HC1 molecules. In solution, however, HCl is called hydrochloric acid and is present as hydrogen ions and chloride ions. 

Internal electrolyte — Electrolyte solution filling the internal chamber of a -> reference electrode or - ion-selective electrode, separated from an external solution by a -> separator. In reference electrodes a constant composition and constant concentration of the internal electrolyte secure a constant potential of the -> electrode. In-... 

The most important application of low concentration behavior of solutes is for solid solutes, especially electrolytes. Electrolyte solutions are examined in detail in chapter 3. Some general thermodynamic methods for describing the properties of very dilute solutions are considered in the following section. 

The discussion focuses on two broad aspects of electrical phenomena at interfaces in the first we determine the consequences of the presence of electrical charges at an interface with an electrolyte solution, and in the second we explore the nature of the potential occurring at phase boundaries. Even within these areas, frequent reference will be made to various specialized treatises dealing with such subjects rather than attempting to cover the general literature. One important application, namely, to the treatment of long-range forces between surfaces, is developed in the next chapter. 

Fig. V-1. Variation of m / o and n /wo with distance for = 51.38 mV and 0.01 M uni-univalent electrolyte solution at 23°C. The areas under the full lines give an excess of 0.90 X 10 mol of anions in a column of solution of 1-cm cross section and a deficiency of 0.32 x 10 mol of cations. There is, correspondingly, a compensating positive surface charge of 1.22 x 10 " mol of electronic charge per cm. The dashed line indicates the effect of recognizing a finite ion size.

It has long been known that the form of a curved surface of mercury in contact with an electrolyte solution depends on its state of electrification [108, 109], and the earliest comprehensive investigation of the electrocapillary effect was made by Lippmann in 1875 [110]. A sketch of his apparatus is shown in Fig. V-10. 

Streaming potential measurements are to be made using a glass capillary tube and a particular electrolyte solution, for example, O.OIM sodium acetate in water. Discuss whether the streaming potential should or should not vary appreciably with temperature. 

H. S. Hamed and B. B. Owen, The Physical Chemistry of Electrolyte Solutions, Reinhold, New York, 1950. 

Rehbinder and co-workers were pioneers in the study of environmental effects on the strength of solids [144], As discussed by Frumkin and others [143-145], the measured hardness of a metal immersed in an electrolyte solution varies with applied potential in the manner of an electrocapillary curve (see Section V-7). A dramatic demonstration of this so-called Rehbinder effect is the easy deformation of single crystals of tin and of zinc if the surface is coated with an oleic acid monolayer [144]. 

Here, x denotes film thickness and x is that corresponding to F . An equation similar to Eq. X-42 is given by Zorin et al. [188]. Also, film pressure may be estimated from potential changes [189]. Equation X-43 has been used to calculate contact angles in dilute electrolyte solutions on quartz results are in accord with DLVO theory (see Section VI-4B) [190]. Finally, the x term may be especially important in the case of liquid-liquid-solid systems [191]. 

Finally, if the sliding surfaces are in contact with an electrolyte solution, an analysis indicates that the coefficient of friction should depend on the applied potential [41]. 

Fig. XIII-10. Properties of colloidal electrolyte solutions—sodium dodecyl sulfate. (From Ref. 102a.)...

Itaya K 1998 In situ scanning tunneling microscopy in electrolyte solutions Prog. Surf. Sc/. 58 121... 

The situation for electrolyte solutions is more complex theory confimis the limiting expressions (originally from Debye-Htickel theory), but, because of the long-range interactions, the resulting equations are non-analytic rather than simple power series.) It is evident that electrolyte solutions are ideally dilute only at extremely low concentrations. Further details about these activity coefficients will be found in other articles. 

Were the FlCl in its standard state, AC would equal where is the standard emf for the reaction. In general, for any reversible chemical cell without transference, i.e. one with a single electrolyte solution, not one with any kind of junction between two solutions. 

We conclude this section by discussing an expression for the excess chemical potential in temrs of the pair correlation fimction and a parameter X, which couples the interactions of one particle with the rest. The idea of a coupling parameter was mtrodiiced by Onsager [20] and Kirkwood [Hj. The choice of X depends on the system considered. In an electrolyte solution it could be the charge, but in general it is some variable that characterizes the pair potential. The potential energy of the system... 

The Debye-Htickel limiting law predicts a square-root dependence on the ionic strength/= MTLcz of the logarithm of the mean activity coefficient (log y ), tire heat of dilution (E /VI) and the excess volume it is considered to be an exact expression for the behaviour of an electrolyte at infinite dilution. Some experimental results for the activity coefficients and heats of dilution are shown in figure A2.3.11 for aqueous solutions of NaCl and ZnSO at 25°C the results are typical of the observations for 1-1 (e.g.NaCl) and 2-2 (e.g. ZnSO ) aqueous electrolyte solutions at this temperature. 

Jacob J, Kumar A, Anisimov M A, Povodyrev A A. and Sengers J V 1998 Crossover from Ising to mean-field critical behavior in an aqueous electrolyte solution Phys. Rev. E 58 2188... 

Card D N and Valleau J 1970 Monte Carlo study of the thermodynamics of electrolyte solutions J. Chem. Phys. 52 6232... 

Friedman H L and Dale W T 1977 Electrolyte solutions at equilibrium Statistical Mechanics part A, Equilibrium Techniques ed B J Berne (New York Plenum)... 

Outhwaite C W 1974 Equilibrium theories of electrolyte solutions Specialist Periodical Report (London Chemical Society)... 

Rasaiah J C 1987 Theories of electrolyte solutions The Liquid State and its Electrical Properties (NATO Advanced Science Institute Series Vol 193) ed E E Kunhardt, L G Christophous and L H Luessen (New York Plenum)... 

Rasaiah J C 1973 A view of electrolyte solutions J. Solution Chem. 2 301... 

Ionic conductors arise whenever there are mobile ions present. In electrolyte solutions, such ions are nonually fonued by the dissolution of an ionic solid. Provided the dissolution leads to the complete separation of the ionic components to fonu essentially independent anions and cations, the electrolyte is tenued strong. By contrast, weak electrolytes, such as organic carboxylic acids, are present mainly in the undissociated fonu in solution, with the total ionic concentration orders of magnitude lower than the fonual concentration of the solute. Ionic conductivity will be treated in some detail below, but we initially concentrate on the equilibrium stmcture of liquids and ionic solutions. 

For an electrolyte solution containing both anions and cations, with the tennmal velocity of the cations being and the number of ions of charge z Cq per unit volume being Et, the product corresponds just... 

The integral equation approach has also been explored in detail for electrolyte solutions, with the PY equation proving less usefiil than the HNC equation. This is partly because the latter model reduces cleanly to the MSA model for small h 2) since... 

In principle, simulation teclmiques can be used, and Monte Carlo simulations of the primitive model of electrolyte solutions have appeared since the 1960s. Results for the osmotic coefficients are given for comparison in table A2.4.4 together with results from the MSA, PY and HNC approaches. The primitive model is clearly deficient for values of r. close to the closest distance of approach of the ions. Many years ago, Gurney [H] noted that when two ions are close enough together for their solvation sheaths to overlap, some solvent molecules become freed from ionic attraction and are effectively returned to the bulk [12]. 

In addition to the case of a metal in contact with its ions in solution there are other cases in which a Galvani potential difference between two phases may be found. One case is the innnersion of an inert electrode, such as platinum metal, into an electrolyte solution containing a substance S that can exist m either an oxidized or reduced fomi tlirough the loss or gain of electrons from the electrode. In the sunplest case, we have... 

Robinson R A and Stokes R H 1959 Electrolyte Solutions (London ButtenA/orth)... 

Martynov G A and Salem R R 1983 Electrical Double Layer at a Metal-Dilute Electrolyte Solution Inteiface (Berlin Springer)... 

One potentially powerfiil approach to chemical imaging of oxides is to capitalize on the tip-surface interactions caused by the surface charge induced under electrolyte solutions [189]. The sign and the amount of the charge induced on, for example, an oxide surface under an aqueous solution is detenuined by the pH and ionic strength of the solution, as well as by the isoelectric point (lEP) of the sample. At pH values above the lEP, the charge is negative below this value. 

Protems can be physisorbed or covalently attached to mica. Another method is to innnobilise and orient them by specific binding to receptor-fiinctionalized planar lipid bilayers supported on the mica sheets [15]. These surfaces are then brought into contact in an aqueous electrolyte solution, while the pH and the ionic strength are varied. Corresponding variations in the force-versus-distance curve allow conclusions about protein confomiation and interaction to be drawn [99]. The local electrostatic potential of protein-covered surfaces can hence be detemiined with an accuracy of 5 mV. 

Simonson J M and Mesmer R E 1994 Electrolyte solutions at high temperatures and pressures Solution Calorimetry, Experimental Thermodynamics yo IV, ed K N Marsh and PAG O Hare (Oxford Blackwell)... 

Figure Bl.28.6. (a) Convection within the electrolyte solution, due to rotation of the electrode (b) Nemst diflfiision model for steady state.

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