Silver ammonia complex iodide

Ores of silver native silver, argentite, cerargyrite (horn silver). Metallurgy of silver cyanide process, amalgamation process, Parkes process. O mpoimds of silver silver oxide, silver chloride, silver bromide, silver iodide, silver ammonia complex, silver cyanide complex, silver thiosulfate complex, silver nitrate. 

EXAMPLE 7-6 Calculate the solubility of silver iodide in 0.01 M ammonia, if the solubility product of silver iodide is 9 x 10 and the logarithms of the successive formation constants of the silver-ammonia complexes are 3.2 and 3.8. 

Only three simple silver salts, ie, the fluoride, nitrate, and perchlorate, are soluble to the extent of at least one mole per Hter. Silver acetate, chlorate, nitrite, and sulfate are considered to be moderately soluble. AH other silver salts are, at most, spatingly soluble the sulfide is one of the most iasoluble salts known. SHver(I) also forms stable complexes with excess ammonia, cyanide, thiosulfate, and the haUdes. Complex formation often results ia the solubilization of otherwise iasoluble salts. Silver bromide and iodide are colored, although the respective ions are colorless. This is considered to be evidence of the partially covalent nature of these salts. 

Silver chloride is readily soluble in ammonia, the bromide less readily and the iodide only slightly, forming the complex cation [Ag(NH3)2]. These halides also dissolve in potassium cyanide, forming the linear complex anion [AglCN) ] and in sodium thiosulphate forming another complex anion, [Ag(S203)2] ... 

Silver Iodide. Silver iodide, Agl, precipitates as a yellow soHd when iodide ion is added to a solution of silver nitrate. It dissolves in the presence of excess iodide ion, forming an Agl2 complex however, silver iodide is only slightly soluble in ammonia and dissolves slowly in thiosulfate and cyanide solutions. 

This result shows that silver iodide will not dissolve in ammonia (though some of the silver ions will be complexed). These results are in good agreement with experimental facts. 

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 of complexing ammonia. Silver bromide is only slightly soluble and silver iodide is insoluble even with the addition of ammonia. Increasing covaicney from lluoride to iodide is expected and decreased solubility in water is observed. 

The alkylation of IbP 1 in an alkaline medium to give the corresponding anion follows another pathway. A mixture of 3-methyl-IbP 41 (in 33-40% yield) and 1-methyl-IbP 228 (in 8-9.3% yield) formed when base 1 was treated with methyl iodide in an alkaline alcoholic solution with cooling. These two substances were quite readily separated because isomer 228 unlike compound 41 formed complexes with silver(l) salts (nitrate or acetate) insoluble in water. The complex was easily decomposed when treated with aqueous ammonia. IbP benzylation by benzylphenyldimethylammonium chloride in alkali gave similar results. Isomers separated as silver salts afforded 3-benzyl-IbP (in 50-52%) and 1-benzyl-IbP (in 15.4-16% yield) (79SUP694511). 

The silver chloride precipitate has to be separated from the original test solution since the ions present here, e.g., the cation of the substance to be examined, can disturb the complexation. Compared to the silver salts of bromide and iodide, silver chloride is the least insoluble. So the formation constant in the above complexation wins in the competition for the silver ion. Silver iodide is more insoluble, and here the precipitate dissolves in ammonia only with difficulty. The silver iodide is not soluble in ammonia at all. 

The precipitate is suspended in 2 ml of water R, and 1.5 ml of ammonia R is added. The precipitate must not dissolve. Silver iodide, compared to silver chloride and bromide, is relatively insoluble. So, where these two salts would dissolve because the silver ion forms a complex with ammonia, is not the case with silver iodide. The reason for isolating the precipitate is to avoid the ions of the original test solution, which could disturb the complex formation. 

The selectivity of the test is quite limited, even compared to the specificity seen in the identification test for chlorides. In the identification three criteria have to be fulfilled to qualify for a positive reaction. The unknown should give a white (curdled) precipitate formed upon addition of silver nitrate, which is insoluble in dilute nitric acid but redissolves in ammonia. In the limit test 2.4.4. Chlorides any substance capable of giving a white or weakly colored precipitate in dilute nitric acid will give a response like chloride, and this should be remembered in case of an xmexpected result. For the sake of example the following ions and substances are capable of giving a false positive reaction bromide, iodide, bromate, iodate, sulfite, chlorate, oxalate, and benzoate. In addition to this a variety of more complex organic substances are likely to precipitate, for example, alkaloids. 

Recall that silver chloride is soluble in an excess of chloride ions by the formation of the ion complex chlorosilver(I) (see Chap. 25). Bromide ions give a clear yellow color of silver bromide that dissolves in the same reagents as the chloride ion but with more difficulty. Iodide ions give a silver iodide precipitate insoluble in ammonia but soluble in potassium cyanide and sodium thiosulfate. From another standpoint, Ag+ ions give silver dithizonate with dithizone. The... 

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