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Interphase electrode-solution forces

In the electrode-solution interphase, the adsorption of these substances is also affected by the influence of the electric field in the double layer on their dipoles. Substances that collect in the interphase as a result of forces other than electrostatic are termed surface-active substances or surfactants. [Pg.210]

When charges are separated, a potential difference develops across the interface. The electrical forces that operate between the metal and the solution constitute the electrical field across the electrode/electrolyte phase boundary. It will be seen that although the potential differences across the interface are not large ( 1 V), the dimensions of the interphase region are very small (—0.1) and thus the field strength (gradient of potential) is enormous—it is on the order of 10 V cm. The effect of this enormous field at the electrode/electrolyte interface is, in a sense, the essence of electrochemistry. [Pg.60]

Thus, according to these theories, all univalent (1 1) electrolytes should behave the same way. However, this is not what was observed experimentally. Solutions of different 1 1 electrolytes (e.g., NaCl, NaBr, Nal, KI) show species-specific behavior. In order to interpret this specific behavior, Grahame (5) proposed a new model of the interphase the triple-layer model. The basic idea in the interpretation of the ion-specific behavior is that anions, when attracted into the interphase, may become dehydrated and thus get closer to the electrode. Each anion undergoes this to a different extent. This difference in the degree of dehydration and the difference in the size of ions results in the specific behavior of the anions. Ions that are partially or fully dehydrated are in contact with the electrode. This contact adsorption of ions allows short-range forces (e.g., electric image forces) to act between the metal elec-... [Pg.48]

The double layer can be divided into two regions the compact double layer that includes the area between the electrode and the plane of closest approach, and the diffuse double layer extending from the plane of closest approach to the bulk of the solution. The compact double layer is also referred to as the Helmholtz double layer or inner double layer [1]. In an outer or diffuse layer the force holding the ions in the interphase is the non-specific Coulombic interaction between the charge on the electrode q (together with that on the inner layer and the charge on the ions [4]. In the inner layer there may or may not be adsorbed ions held partly by Coulombic and partly by specific forces. Potential 02 at the plane of closest approach (separating the inner and outer layers) depends on the electrode potential and concentration of the electrolyte [1]. Potential 0 in the diffuse double layer decreases almost exponentially with distance x from the plane of closest approach, and it can be written [1] ... [Pg.291]

A word of explanation may be needed here. It was said in Section B of Chapter 3 that migration of ions under the influence of electric field is not an important mass transfer mode in fairly concentrated solutions. Here we say that the field of the interphase changes the concentrations of ions. Are these statements not contradictory That this is only an apparent contradiction becomes obvious when we remember that the thickness of the diffusion layer is commonly ten thousand times that of the double layer. Thus it is true that species move most of the distance from the bulk of the solution to the electrode surface in the gradient of forces other than electrical. At the same time the concentration at the electrode surface in the presence of field differs from that in the absence of one. [Pg.72]


See other pages where Interphase electrode-solution forces is mentioned: [Pg.210]    [Pg.51]    [Pg.57]    [Pg.49]    [Pg.39]    [Pg.327]    [Pg.12]    [Pg.68]    [Pg.32]   
See also in sourсe #XX -- [ Pg.11 , Pg.67 , Pg.70 ]




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