Silver halides solubility

Although the data for the silver halides suggest that silver(I) fluoride is likely to be more soluble than the other silver halides (which is in fact the case), the hydration enthalpies for the sodium halides almost exactly balance the lattice energies. What then is the driving force which makes these salts soluble, and which indeed must be responsible for the solution process where this is endothermic We have seen on p. 66 the relationship AG = — TAS and... 

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. 

Silver Chloride. Silver chloride, AgCl, is a white precipitate that forms when chloride ion is added to a silver nitrate solution. The order of solubility of the three silver halides is Cl" > Br" > I. Because of the formation of complexes, silver chloride is soluble in solutions containing excess chloride and in solutions of cyanide, thiosulfate, and ammonia. Silver chloride is insoluble in nitric and dilute sulfuric acid. Treatment with concentrated sulfuric acid gives silver sulfate. 

Iodides can also be determined by this method, and in this case too there is no need to filter off the silver halide, since silver iodide is very much less soluble than silver thiocyanate. In this determination the iodide solution must be very dilute in order to reduce adsorption effects. The dilute iodide solution (ca 300 mL), acidified with dilute nitric acid, is treated very slowly and with vigorous stirring or shaking with standard 0.1 M silver nitrate until the yellow precipitate coagulates and the supernatant liquid appears colourless. Silver nitrate is then present in excess. One millilitre of iron(III) indicator solution is added, and the residual silver nitrate is titrated with standard 0.1M ammonium or potassium thiocyanate. 

Determination of iodide as silver iodide Discussion. This anion is usually determined by precipitation as silver iodide, Agl. Silver iodide is the least soluble of the silver halides 1 litre of water dissolves 0.0035 mg at 21 °C. Co-precipitation and similar errors are more likely to occur with iodide than with the other halides. 

Silver halides dissolve in excess halide (e.g. AgCl is a hundred times more soluble in 1 M HC1 than in water) forming complex ions AgX2 and AgX3 [53]. These isolated anions are not often found in the solid state thus M2AgI3 (M = K, Rb, NH4) have comer linked tetrahedra (Figure... 

Because the fluoride ion is so small, the lattice enthalpies of its ionic compounds tend to be high (see Table 6.6). As a result, fluorides are less soluble than other halides. This difference in solubility is one of the reasons why the oceans are salty with chlorides rather than fluorides, even though fluorine is more abundant than chlorine in the Earth s crust. Chlorides are more readily dissolved and washed out to sea. There are some exceptions to this trend in solubilities, including AgF, which is soluble the other silver halides are insoluble. The exception arises because the covalent character of the silver halides increases from AgCl to Agl as the anion becomes larger and more polarizable. Silver fluoride, which contains the small and almost unpolarizable fluoride ion, is freely soluble in water because it is predominantly ionic. 

Silver(I) does not disproportionate in aqueous solution and, in almost all its compounds, silver has oxidation number +1. Apart from silver nitrate, AgN03, and silver fluoride, silver salts are generally only sparingly soluble in water. Silver nitrate is the most important compound of silver and the starting point for the manufacture of silver halides for use in photography. 

The solubilities of the ionic halides are determined by a variety of factors, especially the lattice enthalpy and enthalpy of hydration. There is a delicate balance between the two factors, with the lattice enthalpy usually being the determining one. Lattice enthalpies decrease from chloride to iodide, so water molecules can more readily separate the ions in the latter. Less ionic halides, such as the silver halides, generally have a much lower solubility, and the trend in solubility is the reverse of the more ionic halides. For the less ionic halides, the covalent character of the bond allows the ion pairs to persist in water. The ions are not easily hydrated, making them less soluble. The polarizability of the halide ions and the covalency of their bonding increases down the group. 

Use of the alloy to reduce metal halides in solvents to the finely divided and highly reactive metals is not recommended for cases where the halide is highly soluble in the solvent (e.g. zinc chloride or iron(III) chloride in THF). Explosive reaction may ensue [1]. The alloys explode violently in contact with silver halides. 

In order for a metathesis reaction to occur in water, some product must be removed from the reaction. Generally, this involves the formation of a precipitate, the evolution of a gas, or the formation of an unionized product. Because solubilities are different in liquid ammonia, reactions are often unlike those in water. Although silver halides are insoluble in water, they are soluble in liquid ammonia as a result of forming stable complexes with ammonia. Therefore, the reaction... 

Formation of water-soluble polymetaphosphimates by reaction of Ag3(P02NH)3 (93) with a halide under formation of silver halide. With the use of (NH4)2S, the ammonium trimetaphosphimate (NH4)3(P02 NH)3 H20 has been obtained (94). 

Hydrogen cyanide (Table 15.1) is a colorless, flammable liquid or gas that boils at 25.7°C and freezes at minus 13.2°C. The gas rarely occurs in nature, is lighter than air, and diffuses rapidly. It is usually prepared commercially from ammonia and methane at elevated temperatures with a platinum catalyst. It is miscible with water and alcohol, but is only slightly soluble in ether. In water, HCN is a weak acid with the ratio of HCN to CN about 100 at pH 7.2, 10 at pH 8.2, and 1 at pH 9.2. HCN can dissociate into H+ and CN. Cyanide ion, or free cyanide ion, refers to the anion CN derived from hydrocyanic acid in solution, in equilibrium with simple or complexed cyanide molecules. Cyanide ions resemble halide ions in several ways and are sometimes referred to as pseudohalide ions. For example, silver cyanide is almost insoluble in water, as are silver halides. Cyanide ions also form stable complexes with many metals. 

B In Example 19-13 we saw that the expression for the solubility, 5, of a silver halide in an aqueous ammonia solution, where [NH3] is the concentration of aqueous ammonia, is given by ... 

These incorporate membranes fabricated from insoluble crystalline materials. They can be in the form of a single crystal, a compressed disc of micro-crystalline material or an agglomerate of micro-crystals embedded in a silicone rubber or paraffin matrix which is moulded in the form of a thin disc. The materials used are highly insoluble salts such as lanthanum fluoride, barium sulphate, silver halides and metal sulphides. These types of membrane show a selective and Nemstian response to solutions containing either the cation or the anion of the salt used. Factors to be considered in the fabrication of a suitable membrane include solubility, mechanical strength, conductivity and resistance to abrasion or corrosion. 

An additional point worth mentioning is that the potentiometric method can monitor several partially soluble salts at once. For example, if a solution contains chloride, bromide and iodide ions, then a plot of emf against the volume of cation (e.g. Ag ) will contain three inflection points (see Figure 4.8), one for each of the three silver halides. for Agl is smaller than that for AgCl, while (AgBr) has an intermediate value, so the first inflection point represents the precipitation of Agl, the second represents formation of AgBr and the third represents the formation of insoluble AgCl. ... 

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]). 

An improvement [325] in the properties of the halide ISE, both in increased sensitivity and decreased light sensitivity can be attained by using a mixture of silver halide and Ag2 S, which is far less soluble than any of the silver halides. The other ISE properties do not change. The ise versus log a dependence is thus identical with the dependence for a pure silver halide membrane [288]. This system is used in most commercial ISEs. 

The ISEs described in this section are useful primarily for determination of halide ions by direct potentiometry, where the silver halide in the membrane is identical with the determinand. As follows from the discussion on p. 48 an electrode made of a less soluble silver halide X can be used to determine other halide Y" if the condition... 

In a modified and more complicated form (pre-fixation physical development) the exposed sensitive layer is placed directly in the developing solution without first dissolving out the silver halide. The developing solution contains a silver halide solvent in addition to the soluble silver salt, and part of the developed silver in this process comes from the original silver halide. Some direct development also occurs. 

Reduction of Double Complexes. Except for Ag/Au bimetallic nanoparticles, bimetallic nanoparticle dispersions containing Ag have not been studied extensively. One of the possible reasons is that an Ag1 ion readily reacts with a halide ion to produce water-insoluble silver halide. Also, many other water-soluble metal salts other than halides are not as suitable as precursors for the production of metallic particles by mild reduction. 

Halides (confined at present to silver halides) can be deposited by hydrolyzing a water-soluble halogeno-alcohol (halohydrin) to slowly form halide ions in the presence of Ag ions ... 

The solubility products of most halides are much higher in general than those of chalcogenides. Those of the silver halides are fairly low, which allows these depositions to take place readily. 

How can you explain the change in the colour of the silver halides with an increase in the atomic number of the halogen Compare the solubility products of silver halides and sulphide (see Appendix 1, Table 12). What anion is the most sensitive reagent for the silver ion What is the significance of silver halides in photography What substances are used in developing photographs ... 

The extra field of the subgroup ions certainly plays a part in the low solubility of these compounds, but it cannot be said that this alone reduces solubility since AgF, in which the fluorine ion is particularly small, is freely soluble in contrast to AgCl and the other silver halides. It must be kept in mind that, in general, lattice energy... 

The formation of these relatively stable complex salts explains the solubility of the silver halides in sodium thiosulphate solution and the value of such a solution for fixing photographic prints. In many cases the complex salts have been isolated in the solid state,10 for example,... 

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