Ions, adsorption substances

It has been noted that for substances which do not yield ions in solution, such as charcoal, the charge is always produced by the preferential adsorption of an ion from the solution, e.g. the hydrogen ion. For substances which yield ions in solution, e.g. the hydroxides, it is evident that the charge can be accounted for by superficial ionisation (see Zsigmondy, Kolloidchemie Wolfgang-Pauli, Trans. Farad. Soc. xvi. 6,1921), e.g. ... 

Besides water and ions, other substances can also be adsorbed on both the external and internal surfaces. Since the surface of rocks and soils is strongly hydrophilic on a macroscopic scale, hydrophilic substances are more strongly adsorbed than hydrophobic substances. Some authors, however, say that the hydrophilic-hydrophobic character strongly varies on molecular scale. So the oxygen atoms next to the isomorphic substitutions are hydrophilic, while the oxygen atoms far from them are hydrophobic. The hydrophobic oxygen atoms are, for example, responsible for the adsorption of hydrophobic pesticides (Laird 2004). 

The soil pH considerably affects soil characteristics. It is important for many soil-forming processes and it also affects the biological activity of soil organisms. The soil pH directly affects particularly the solubility of many substances, ion adsorption and desorption, coagulation and peptization of colloids and chemical reactions. By its action on the soil structure it also affects most of the physical properties of the soil. Thus, the soil pH is an important parameter of the soil fertility. 

The adsorption constant is characteristic for the surface enrichment of a substance. For the description of ion adsorption the strong electrostatic forces between the ions must be taken into account. The first equation applicable to these problems was the Frumkin isotherm. ... 

Most substances acquire a surface charge when brought into contact with a polar medium because of chemical reaction at the interface. The charging mechanisms include ionization, ion adsorption, and ion dissolution [1]. Charge separation occurs at the solid/liquid interface when a particle is suspended in a liquid solution. As shown in Fig. 1, a negatively charged particle is surrounded by a diffuse layer... 

Adsorption at the solid-liquid interface is generally similar to the adsorption at the solid phase-gaseous phase interface. Theoretical modelling of the adsorption process is more difficult because, in addition to adsorbing dissolved substances, solvent is present (e.g. water), the molecules of which can also adsorb, and interactions of adsorbed molecules with molecules of the solvent may occur. Molecular adsorptions, when molecules of a substance are adsorbed, and ion adsorptions, in which ions of a substance are adsorbed, can similarly take place. Solid phase-liquid phase interfaces are usually described by empirical equations and theoretically derived equations of the Freundlich and Langmuir type. 

The third technique, proposed by Schlapp (512) in 1925, depends not upon precipitation of these hormonal substances, but also on selective adsorption and elution. Potts and Gallagher (477) reviewed both the methods and the adsorbants, which latter are ion-exchange substances to a greater or lesser degree, and which retain vasopressin more strongly... 

To apply these various equations to the adsorption of a gas on a solid, it is necessary to consider the interaction of the surface layers of a solid composed of atoms (or ions) of a substance Y, say, with isolated molecules of gas X. The individual interactions of each atom in gas molecule X with each atom of the solid Y have to be added up to obtain the potential 0(z) of a single molecule of the gas with reference to the solid ... 

Adsorption of Metal Ions and Ligands. The sohd—solution interface is of greatest importance in regulating the concentration of aquatic solutes and pollutants. Suspended inorganic and organic particles and biomass, sediments, soils, and minerals, eg, in aquifers and infiltration systems, act as adsorbents. The reactions occurring at interfaces can be described with the help of surface-chemical theories (surface complex formation) (25). The adsorption of polar substances, eg, metal cations, M, anions. A, and weak acids, HA, on hydrous oxide, clay, or organically coated surfaces may be described in terms of surface-coordination reactions ... 

An important feature of such films is their low ionic conductivity that restricts cation transport through the film substance. Electronic semiconduction, however, permits other electrode processes (oxidation of H2O to O2) to take place at the surface without further significant film growth. At elevated anodic potentials adsorption and entry of anions, particularly chloride ions, may lead to instability and breakdown of these protective films (Sections 1.5 and 1.6). 

We express the altered concentration in terms of the adsorption excess. If all the adsorbed substance were contained to the extent of k gr. per cm.2 on a superficial layer of zero thickness and surface total mass present in the volume Y would be m = V + kto. The layer of altered concentration must, however, have a certain thickness. We will therefore imagine a plate 2 placed in front of the surface and parallel to it, and define the adsorption excess as the concentration in the included layer minus the concentration in the free liquid. That this result is independent of the arbitrarily chosen thickness is easily proved when we remember that the problem is exactly the same as that of finding the change of concentration around an electrode in the determination of the transport number of an ion by Hittorf s method. 

The adsorption excesses of the ions were calculated according to 203. Substances were divided into three classes according as... 

Adsorption and ion exchange chromatography are well-known methods of LC. In adsorption, one frequently selects either silica or alumina as stationary phase for separation of nonionic, moderately polar substances (e.g. alcohols, aromatic heterocycles, etc.). This mode works best in the fractionation of classes of compounds and the resolution of isomeric substances (J). Ion exchange, on the other hand, is applicable to the separation of ionic substances. As to be discussed later, this mode has been well developed as a tool for analysis of urine constituents (8). 

Adsorption of surface-active substances is attended by changes in EDL structure and in the value of the / -potential. Hence, the effects described in Section 14.2 will arise in addition. When surface-active cations [NR] are added to an acidic solution, the / -potential of the mercury electrode will move in the positive direction and cathodic hydrogen evolution at the mercury, according to Eq. (14.16), will slow down (Fig. 14.6, curve 2). When I ions are added, the reaction rate, to the contrary, will increase (curve 3), owing to the negative shift of / -potential. These effects disappear at potentiafs where the ions above become desorbed (at vafues of pofarization of less than 0.6 V in the case of [NR]4 and at values of polarization of over 0.9 V in the case of I ). 

A condition for inhibitor action is its adsorption on the metal at the open-circuit potential. Nentral inhibitor molecnles wiU not adsorb when this potential is far from the metal s point of zero charge (see Section 10.4.2). In this case, inhibitors forming ions are nsed cations (e.g., from amino compounds) or anions (from compounds with suKo groups), depending on the sign of surface charge. Inhibitor action is often enhanced greatly when mixtures of several substances are used. 

On the surface of metal electrodes, one also hnds almost always some kind or other of adsorbed oxygen or phase oxide layer produced by interaction with the surrounding air (air-oxidized electrodes). The adsorption of foreign matter on an electrode surface as a rule leads to a lower catalytic activity. In some cases this effect may be very pronounced. For instance, the adsorption of mercury ions, arsenic compounds, or carbon monoxide on platinum electrodes leads to a strong decrease (and sometimes total suppression) of their catalytic activity toward many reactions. These substances then are spoken of as catalyst poisons. The reasons for retardation of a reaction by such poisons most often reside in an adsorptive displacement of the reaction components from the electrode surface by adsorption of the foreign species. 

Thus, the HLB of an ionic surface-active substance is balanced at the standard ion-transfer potential. This is simply a reinterpretation of the definition of Aq P, but is a very important relation, which is valid no matter what the actual form of the adsorption... 

The electrical oscillations at the aqueous-organic interface or at membranes in the absence of any substances relative to the channel or gate were introduced. These oscillations might give some fundamental information on the electrical excitability in living organisms. Since the ion transfer at the aqueous-organic or aqueous-membrane interface and the interfacial adsorption are deeply concerned in the oscillation, it has been stressed that the voltammetry for the ion transfer at an interface of two immiscible electrolyte solutions is... 

Freeze Conceit tret ion Hater sample is partially frozen, concentrating the dissolved substances in the unfrozen portion. All sample types Minimizes sample losses due to volatilization or chemical modification. Principal losses occur due to occlusion, adsorption, evaporation and channelling in the ice layer. Limited sample size. 

Adsorption is a physicochemical process whereby ionic and nonionic solutes become concentrated from solution at solid-liquid interfaces.3132 Adsorption and desorption are caused by interactions between and among molecules in solution and those in the structure of solid surfaces. Adsorption is a major mechanism affecting the mobility of heavy metals and toxic organic substances and is thus a major consideration when assessing transport. Because adsorption is usually fully or partly reversible (desorption), only rarely can it be considered a detoxification process for fate-assessment purposes. Although adsorption does not directly affect the toxicity of a substance, the substance may be rendered nontoxic by concurrent transformation processes such as hydrolysis and biodegradation. Many chemical and physical properties of both aqueous and solid phases affect adsorption, and the physical chemistry of the process itself is complex. For example, adsorption of one ion may result in desorption of another ion (known as ion exchange). 

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