Silver halides, dissolution

The method may also be applied to the analysis of silver halides by dissolution in excess of cyanide solution and back-titration with standard silver nitrate. It can also be utilised indirectly for the determination of several metals, notably nickel, cobalt, and zinc, which form stable stoichiometric complexes with cyanide ion. Thus if a Ni(II) salt in ammoniacal solution is heated with excess of cyanide ion, the [Ni(CN)4]2 ion is formed quantitatively since it is more stable than the [Ag(CN)2] ion, the excess of cyanide may be determined by the Liebig-Deniges method. The metal ion determinations are, however, more conveniently made by titration with EDTA see the following sections. 

The approximation (3.4.28) is fulfilled for dissolution of all silver halides in cyanide ion solutions. Even in the case of the least soluble haUde, Agl, the solubility product equals 10, while Ag(CN)j varies between 10 and I0 8s (see [5]). 

The use of ISEs in non-aqueous media(for a survey see [125,128]) is limited to electrodes with solid or glassy membranes. Even here there are further limitations connected with membrane material dissolution as a result of complexation by the solvent and damage to the membrane matrix or to the cement between the membrane and the electrode body. Silver halide electrodes have been used in methanol, ethanol, n-propanol, /so-propanol and other aliphatic alcohols, dimethylformamide, acetic acid and mixtures with water [40, 81, 121, 128]. The slope of the ISE potential dependence on the logarithm of the activity decreases with decreasing dielectric constant of the medium. With the fluoride ISE, the theoretical slope was found in ethanol-water mixtures [95] and in dimethylsulphoxide [23], and with PbS ISE in alcohols, their mixtures with water, dioxan and dimethylsulphoxide [134]. The standard Gibbs energies for the transfer of ions from water into these media were also determined [27, 30] using ISEs in non-aqueous media. 

Traditionally, potentiometric sensors are distinguished by the membrane material. Glass electrodes are very well established especially in the detection of H+. However, fine-tuning of the potentiometric response of this type of membrane is chemically difficult. Solid-state membranes such as silver halides or metal sulphides are also well established for a number of cations and anions [25,26]. Their LOD is ideally a direct function of the solubility product of the materials [27], but it is often limited by dissolution of impurities [28-30]. Polymeric membrane-based ISEs are a group of the most versatile and widespread potentiometric sensors. Their versatility is based on the possibility of chemical tuning because the selectivity is based on the extraction of an ion into a polymer and its complexation with a receptor that can be chemically designed. Most research has been done on polymer-based ISEs and the remainder of this work will focus on this sensor type. 

The useful concentradon of emulsion is in the range of 20-50 mg of emulsion per mL of developer. It should be noted, however, that the number of emulsion pieces influences the developing speed, because the silver halide in the emulsion is only slowly soluble in the sodium sulflte incorporated in the developer, and the larger surfaces of several small emulsion pieces accelerate the dissolution of the silver halide. Similarly, the time of stirring the developer, before the section is put on, influences the concentration of silver ions, and thus, the developing speed. 

Nitric acid dissolves silver at all concentrations. This is the principal chemical reaction for the dissolution of silver into the soluble nitrate, which is the chemical intermediate for the production of electroplated ware, catalysts, battery plates, pharmaceuticals, mirrors, and silver halides for photographic materials. Nitric acid removes silver from the residual pellet in the gold fire assay. 

Unequal dissolution of oppositely charged ions of which the solid phase may be composed (e.g., silver halide particles suspended in water). 

Thus films can be divided into two groups according to their morphology. Discontinuous films are porous, have a low resistance and are formed at potentials close to the equilibrium potential of the corresponding electrode of the second kind. They often have substantial thickness (up to 1 mm). Films of this kind include halide films on copper, silver, lead and mercury, sulphate films on lead, iron and nickel oxide films on cadmium, zinc and magnesium, etc. Because of their low resistance and the reversible electrode reactions of their formation and dissolution, these films are often very important for electrode systems in storage batteries. 

The solubility product depends on the overall silver ion concentration at the membrane surface and on the concentration of halide ions resulting from dissolution of the membrane, [X"]soi,... 

Alcohols, hydrocarbons, and their halide-containing derivatives, and their mixtures, are the most frequently used solvents (Solv). The majority of these reactions take place at room temperature or with slight heating, necessary for dissolution of the reagents. The transformation (3.199) was one of the first template reactions of the examined type [434]. In this reaction, the coordinatively unsaturated platinum complex is an N-base and silver nitrate is a Lewis acid ... 

To prepare a film one allows a solution of the sample to evaporate slowly on the face of a suitable window material. The plate may be gradually heated if necessary. For many compounds this means dissolution in a volatile organic solvent, and an alkali halide plate is used. Films of such substances as proteins and mucopolysaccharides have frequently been cast from aqueous solution on a silver chloride plate. IRTRAN-2 (ZnS) and KRS-5 (thallium bromoiodide) plates can also be used. 

An alternate reference system to that of the H2 electrode is the AglAgCl reference electrode. Due to the difference in solvation ability of PlLs compared to ILs, the dissolution of halide salts such as KCl is far more readily accomplished. As such some researchers have constructed AglAgClIKCl (saturated in PlLs) reference electrode systems [92,93]. This reference electrode exhibits a very stable potential of 0.216 V vs. SHE [92, 93]. Experimentally the reference electrode is constructed by placing a silver wire with a AgCl surface layer into a reference compartment containing a saturated solution of KCl in the PIL of choice. 

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