Silver iodide reduction

Although silver iodide is the least photosensitive of the three halides, it has the broadest wavelength sensitivity in the visible spectmm. This feature makes silver iodide particularly useful in the photographic industry. It resists reduction by metals, but is reduced quantitatively by zinc and iron in the presence of sulfuric acid. 

Silver iodide, 14 370, 22 671 in cloud seeding, 22 685 natural occurrence of, 22 668 Silver ion activity, in photographic crystal growth, 19 179 Silver-ion reduction... 

Methyl 3,4-isopropylidene-a-L-fucopyranoside was converted into the 2-tosyl derivative (LXXXII). After removing the isopropylidene residue with methanolic hydrogen chloride, methyl 3,4-dimethyl-2-tosyl-a-L-fucopyranoside (LXXXIII) was obtained by methylation with methyl iodide and silver oxide. Reductive fission of the p-toluenesulfonyl residue with sodium amalgam, followed by hydrolysis, gave 3,4-dimethyl-L-fucose83 (LXXXIV). 

The interference of copper, nickel, cobalt, iron, chromium, and magnesium is prevented by adding sodium potassium tartrate to the test solution only silver (removed as silver iodide by the addition of a little KI solution) and mercury then interfere. Mercury is best removed by adding a little sodium potassium tartrate, a few crystals of hydroxylamine hydrochloride, followed by sodium hydroxide solution until alkaline the mercury is precipitated as metal. Tin(II) chloride is not suitable for this reduction since most of the cadmium is adsorbed on the mercury precipitate. 

Cobalt is determined spectrophotometrically using the absorption spectrum of CoCU " in 10 M hydrochloric acid. Iodine is determined by precipitation of silver iodide after reduction of the complex with sulfur dioxide. Titratable H" " is determined by a potentiometric pH titration. AnaL Calcd. for H3[Co4l3024Hi2] 3H20 Co, 22.04 I, 35.59 titratable H+, 0.282 ratio CorlrH" " = 1 0.75 0.75. Found Co, 22.0 I, 35.45 titratable H", 0.285 ratio Co.T H = 1 0.75 0.75. 

Nickel is determined by the gravimetric dimethyl-glyoxime procedure after reduction of the compound with sulfur dioxide and hydrochloric acid. Iodine is determined as silver iodide after reduction with sulfur dioxide in sulfuric acid medium. Total active oxygen is calculated by measuring the quantity of iodine liberated from potassium iodide in acidic solution. Alkali metals are determined as sulfates in the filtrates from the nickel determinations. 

Silver iodide (K p = 8.51 x 10 ) is less soluble than AgCl in aqueous solution, and so reduction of Ag(I) in the form of solid Agl is thermodynamically less favourable than reduction of AgCl (see problem 7.11 at the end of the chapter). However, Agl is much more soluble in aqueous KI than AgCl is in aqueous KCl solution. The species present in the iodide solution is the complex [Agl3] , the overall stability constant (see Section 6.12) for which is sslO " (equation 7.32). Following a similar procedure to that detailed above, we can use this value to determine that the... 

The residue containing silver iodide is freed from organic matter by extraction with a suitable solvent, dried, and ground to pass a 40-mesh sieve. The powdered residue is shaken with sufficient concentrated ammonia (sp. gr. 0.90) to dissolve all soluble silver salts. The suspension is filtered on a Bilchner funnel and the filtrate (I) is reserved for subsequent recovery of silver by reduction with sodium dithionite solution. 

It is desirable to know the weight of silver iodide because a subsequent reaction involving the reduction of iodic acid with sodium dithionite requires exact quantities. 

In addition to the use of the standard potential ( ), reaction potentials may also be reported with the convention of electromotive force (emfor S [V]). The convention of emf was adopted to make the calculation of cell potentials, from the combination of two half-reactions, more straightforward. For a reduction reaction, the standard potential and the cm/have the same value, while for the same reaction written in the direction of oxidation (e.g the reverse reaction), their signs are opposite. Using the example of a silver iodide cell, consider the complete cell schematic ... 

In the distillation method, iodide carrier was added to the sample, an oxidation-reduction cycle was carried out, and molecular iodine was distilled into carbon tetrachloride. (In the oxidation-reduction cycle, iodide was oxidized to iodate by permanganate in sulfuric acid solution and any elemental bromine and chlorine activities formed were distilled off.) Iodine was back-extracted as iodide into water from the carbon tetrachloride by means of acid sulfite and silver iodide was precipitated. 

Urine samples were also prepared for analysis for radioiodine by oxidative destruction (105). Iodide carrier, sulfuric acid, and solid potassium permanganate were added to a sample and the mixture was boiled under reflux to oxidize the carrier to lodate. Then the following steps were performed reduction of lodate to free Iodine by oxalic acid distillation of the iodine into water reduction to iodide by sulfurous acid and precipitation of silver Iodide. The chemical yield was 84% the standard deviation 4%. 

Titanium diiodide may be prepared by direct combination of the elements, the reaction mixture being heated to 440°C to remove the tri- and tetraiodides (145). It can also be made by either reaction of soHd potassium iodide with titanium tetrachloride or reduction of Til with silver or mercury. 

Iodide ions reduce Cu to Cu , and attempts to prepare copper(ll) iodide therefore result in the formation of Cul. (In a quite analogous way attempts to prepare copper(ll) cyanide yield CuCN instead.) In fact it is the electronegative fluorine which fails to form a salt with copper(l), the other 3 halides being white insoluble compounds precipitated from aqueous solutions by the reduction of the Cu halide. By contrast, silver(l) provides (for the only time in this triad) 4 well-characterized halides. All except Agl have the rock-salt structure (p. 242). Increasing covalency from chloride to iodide is reflected in the deepening colour white yellow, as the... 

---