Silver chloride dissolution

JV Macpherson, PR Unwin. Scanning electrochemical microscopy as a probe of silver-chloride dissolution kinetics in aqueous solutions. J Phys Chem 99 14824-14831, 1995. 

Macpherson JV, Unwin PR (1996) Scanning electrochemical microscope-induced dissolution theory and experiment for silver chloride dissolution kinetics in aqueous solution without supporting electrolyte. J Phys Chem 100(50) 19475-19483. doi 10.1021/jp9614862... 

Generally, such a remarkable restriction of metal dissolution results not only from the formation of a thin surface oxide film but also from the formation of a comparatively thick film such as silver chloride or zinc chloride. In this chapter, however, we use the term passive film only for compact and thin oxide films. 

As examples of some water-soluble salts, mention may be made of potassium chloride, copper sulfate, and sodium vanadate. As examples of some water-insoluble salts, mention may be made of some typical ones such as lead chloride, silver chloride, lead sulfate, and calcium sulfate. The solubilities of most salts increases with increasing temperature. Some salts possess solubilities that vary very little with temperature or even decline. An interesting example is provided by ferrous sulfate, the water solubility of which increases as temperature is raised from room temperature, remains fairly constant between 57 and 67 °C, and decreases at higher temperatures to below 12 g l-1 at 120 °C. Table 5.2 presents the different types of dissolution reactions in aqueous solutions, and Table 5.3 in an indicative way presents the wide and varied types of raw materials that different leaching systems treat. It will be relevant to have a look at Table 5.4 which captures some of the essential and desirable features for a successful leaching system. 

Fig. 9-6. Adaorption coverage of a reaction intermediate of hydroxo-complezes in anodic dissolution of a metallic iron electrode as a function of electrode potential in acidic sulfate solutions at pH 1.0, 2.0 and 3.0 solution is 0.5 M (Ns2S04 + H2SO4) at room temperature. Oqh adsorption coverage of reaction intermediates FeOH,4 and PeOH Vss = volt referred to the saturated silver-silver chloride electrode. [Prom Tsuru, 1991.]...

Addition of an excess of anhydrous aziridine to silver chloride resulted in dissolution and the formation of a colourless solution. Attempts to isolate a complex were unsuccessful and addition of water, ethanol or ether caused reprecipitation of silver chloride. 

Figure 26.12 Measuring setup for investigation of the dissolution of drugs from pharmaceutical preparations T, thermometer K, stirrer P, peristaltic pump E, silicone-rubber-based electrode E2, silver-silver chloride reference electrode. [From Ref. 169.]...

Dissolution occurring by a surface reaction is often slower than by transport-controlled kinetics because the latter results from more rapid surface detachment. There appears to be a good correlation between the solubility of a mineral and the rate-controlling mechanism for dissolution. Table 7.1 lists dissolution rate-controlling mechanisms for a number of substances. The less soluble minerals all dissolve by surface reaction-controlled kinetics. Silver chloride is an exception, but its dissolution... 

The concentrations of ions in equilibrium with a sparingly soluble salt are sufficiently low that the Nernst equation can be used with little error. Rather than measuring the concentration of the relevant ions directly, the more common procedure is to set up a cell in which one of the electrodes involves the insoluble salt, and whose net cell reaction is just the dissolution of the salt. For example, to determine the Ksp for silver chloride, we could use the cell... 

Ag(s) I Ag+ ( M) Ag+,C1- AgClfe) Agfe) whose net equation corresponds to the dissolution of silver chloride ... 

In fact, each electron transfer half-reaction involves a free energy change following this formula. To reach the total variation in AG we sum the contributions of the two half-reactions, remembering that one is a reduction and the other an oxidation. For example, for the dissolution of silver chloride under standard conditions... 

Silver alloys present similar problems and the silver content can be determined after dissolution of 5—10 mg in 1 ml of 50% nitric acid. The tin and gold present will appear as a black residue which may be taken up in 1.5 ml concentrated hydrochloric acid, which of course precipitates silver chloride. The precipitate is removed by centrifugation. Thus again two solvents are required to determine the normal range of elements, e.g. bismuth, copper, gold, lead, silver and tin. 

To examine these effects, investigations were carried out on the dissolution of electrochemically grown films and pressed pellets of silver chloride in 0.1 mol dm-3 aqueous potassium nitrate and in water (6,7). Silver chloride was an ideal system since the kinetics and mechanisms controlling dissolution were unresolved by conventional approaches, despite a number of... 

The equilibrium formation and dissolution of precipitates can be illustrated with silver chloride. Ag+forms a series of chloro complexes, at least up to AgCI4 v. In the presence of solid AgCl the formal description is most readily characterized by the following formalism ... 

A number of anions form slightly soluble precipitates with certain metal ions and can be titrated with the metal solutions for example, chloride can be titrated with silver ion and sulfate with barium ion. The precipitation equilibrium may be affected by pH or by the presence of complexing agents. The anion of the precipitate may be derived from a weak acid and therefore combine with protons in acid solution to cause the precipitate to dissolve. On the other hand, the metal ion may complex with a ligand (the complexing agent) to shift the equilibrium toward dissolution. Silver ion will complex with ammonia and cause silver chloride to dissolve. 

Determine the equilibrium constant for the dissolution and dissociation of silver chloride in water, and the silver chloride solubility in water. 

After studying the interference effects of ten main potential interference ions in the determination of chloride by silver chloride precipitation, Valcarcel s group has shown that the FI approach exhibited 2-12 fold greater tolerance to the interfering ions when compared to the batch manual counterpart, all performed without precipitate dissolution [3,15]. These authors concluded that the improved selectivity of continuous precipitation... 

The determination of chloride involves the precipitation of chloride with silver nitrate, dissolution of the precipitate in ammonia, and determination of silver in the resulting solution by FAAS using air-acetylene or air-hydrogen flames. Standard silver nitrate solutions in ammonia are used for calibration since bromide and iodide interfere in the determination of chloride. 

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. 

---