Silver halides in water

Hard-soft properties account for the differences in behavior of hydrogen halides and silver halides in water ... 

Figure 18.1. Solubility equilibria of silver halides in water ( ) and in sodium halide solutions. (According to K. H. Lieser, Z. Anorg. Allg. Chem., 229, 97 (1957).)...

Relative solubilities of halides. The solubilities of silver halides in water decrease, going down the column of halogens in the periodic table ... 

J. Nedoma, Chem. Listy., 66, 71 (1971). Solubility products of silver halides in water, methanol, n-propanol and their mixtures with water. 

A second area in which polarization effects show up is the solubility of salts in polar solvents such as water. For example, consider the silver halides, in which we have a polarizing cation and increasingly polarizable anions. Silver fluoride, which is quite ionic, is soluble in water, but the less ionic silver chloride is soluble only with the inducement ofcomplexing ammonia. Silver bromide is only slightly soluble and silver iodide is insoluble even with the addition of ammonia. Increasing covalency from fluoride to iodide is expected and decreased solubility in water is observed. 

Refluxing triorgano telluronium halides with silver carboxylate in water yields triorgano telluronium carboxylates8 10. 

The quaternary iodides are crystalline compounds, form platini-chlorides, and with chlorine yield iododicMorides of the type R4ASI.CI2. Some aliphatic-aromatic arsonium iodides combine with metallic salts such as mercwic halides, auric chloride, and cadmiumiodide, whilst iodoform also forms addition compounds with some derivatives. Treatment of the iodides with a boiling suspension of silver chloride replaces the iodine by chlorine, giving R4ASCI. The latter also results when hydrochloric add is added to hydroxides of the type R4AS.OH. The hydroxides are derived from the iodides by boiling the latter with a suspension of silver oxide in water or alcohol. It is not always possible to isolate a crystalline product from this reaction, and the syrups often isolated soon absorb carbon dioxide from the air. 

From relative solubilities (eqn. 20) of silver halides in DMSO and in water (Lnehrs e< ol., 1966) (cf. Table 5). From partial molar heats of solution of tetraethylammonium halides in DMSO and in water. (Arnett and McKelvey, 1966). 

Scattered data for several other aprotic amides exist. Pistoia and Scrosati have reported the solubilities for several alkali and alkaline earth metal halides and transition metal halides in JV,JV-dimethylacet-amide. The solubilities increase in the order Cl < Br < I. Alexander and co-workers have reported solubility product values for numerous silver salts in DMA. They have also reported values for silver salts, KBr and NaCl in hexamethylphosphorotriamide (HMPT). The solubilities of the silver halides in both these solvents follow the same trend as they do in water. Coleman has measured the solubilities and activity coefficients of sodium and potassium chlorides in several dialkylamides containing water. Distribution coefficients of the salt between water and amide have also been calculated. 

Butler et /.citt.ciss.cisg made detailed studies on the solubilities of the silver halides in PC and its mixtures with water. The results follow the general pattern of aprotic solvents in that the salt AgX is soluble in excess halide, the predominant species being AgX. Polynuclear silver species were not found. A summary of these data (molar units) is given in Table 2.7.17. 

Add 1 drop of a liquid or 5 drops of a concentrated ethanolic solution of the unknown solid to 2 mL of a 2% ethanolic silver nitrate solution. If no reaction is observed after 5 minutes at room temperature, heat the solution in a hot water bath at about 100°C, and note whether a precipitate forms. If a precipitate forms, add 2 drops of 5% nitric acid, and note whether the precipitate dissolves. Carboxylic acids give a false test by precipitating in silver nitrate, but they dissolve when nitric acid is added. Silver halides, in contrast, do not dissolve in nitric acid. 

The synthesis of the homoleptic platinumfll) aqua-dication via halide abstraction illustrates the utility of silver salts in such processes. For many years workers were unable to prepare [Pt(H20>4]2+ and Livingstone contended that the complex does not form. However, in 1976 Elding prepared [Pt(H20)4]2+uia chloride abstraction with a silver salt, demonstrating that when K2[PtCl4] is reacted with an excess of silver perchlorate in water, flie reaction proceeds as shown in Scheme 3.7 ... 

When halide abstraction reactions are performed with silver salts in water or in non-aqueous solutions, halide ions are abstracted according to the solubility product of the silver halide (Table 3.1) with the least soluble salts being the first to be precipitated. Abstraction follows the sequence I > Br> Cl" > F". Accordingly, then, the interaction of [NbCl2lCp2l with one mole equivalent of silver perchlorate in acetone leads to the formation of [NbCl2(Me2C0)Cp2][C104] and precipitation of Agl.22... 

Many ionic halides dissolve in water to give hydrated ions. The solubility of a given halide depends on several factors, and generalisations are difficult. Ionic fluorides, however, often differ from other halides in solubility. For example, calcium fluoride is insoluble but the other halides of calcium are highly soluble silver fluoride. AgF, is very soluble but the other silver halides are insoluble. 

To determine which halogen is present, take 1-2 ml. of the filtrate from the sodium fusion, and add dilute sulphuric acid until just acid to litmus. Add about 1 ml. of benzene and then about 1 ml. of chlorine water and shake. A yellowish-brown colour in the benzene indicates bromine, and a violet colour iodine. If neither colour appears, the halogen is chlorine. The result may be confirmed by testing the solubility of the silver halide (free from cyanide) in dilute ammonia solution silver chloride is readily soluble, whereas the bromide dissolves with difficulty, and the iodide not at all. 

Principle. A known weight of the substance is heated with fuming nitric acid and silver nitrate in a sealed tube. The organic material is thus oxidised to carbon dioxide and water, whilst the halogen is converted quantitatively into the corresponding silver halide. The latter js subsequently washed out of the tube, filtered and weighed. 

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