Silver chloride reduction

Silicon, higher chlorides of, 42 Silicon tetrabromide, 38, 40 Silicon tetrachloride, 44 Silicopropane, octachloro, 44 Silicotungstic acid, 129 analysis, 131 ether complex, 131 Silver, metallic, 4 Silver chloride, reduction of, 3 Silver cyanamide, 98 Silver residues, purification of, 2 Sodium amalgam, 10 Sodium amide, 74 Sodium azide, purification of, 79 Sodium azidodithiocarbonate, 82 Sodium butoxide, 88 Sodium hypochlorite (solution), 90 Sodium iodate, 168 Sodium metaperiodate, 170 Sodium paraperiodate, chlorine method, 169 persulfate method, 170 Strontium amalgam, 11 Sulfur hexafluoride, 121 Sulfuryl chloride, 114... 

Birss V I and Smith C K 1987 The anodic behaviour of silver in chloride solutions-l. The formation and reduction of thin silver chloride films Electrochim. Acta 32 259-68... 

Determination of chlorate as silver chloride Discussion. The chlorate is reduced to chloride, and the latter is determined as silver chloride, AgCl. The reduction may be performed with iron(II) sulphate solution, sulphur dioxide, or by zinc powder and acetic (ethanoic) acid. Alkali chlorates may be quantitatively converted into chlorides by three evaporations with concentrated hydrochloric acid, or by evaporation with three times the weight of ammonium chloride. 

Determination of perchlorate as silver chloride Discussion. Perchlorates are not reduced by iron (II) sulphate solution, sulphurous acid, or by repeated evaporation with concentrated hydrochloric acid reduction occurs, however, with titanium(III) sulphate solution. Ignition of perchlorates with ammonium... 

C19-0061. Draw a sketch that shows a molecular view of the charge transfer processes that take place at a silver-silver chloride electrode in contact with aqueous HCl, undergoing reduction ... 

The reaction is complete when the liquid becomes black, due to reduction of the osmic acid. Silver chloride was then removed by filtration and the... 

Watling [491] has described an analytical technique for the accurate determination of mercury at picogram per litre levels in fresh and seawater. Mercury, released by tin (II) chloride reduction of water samples is amalgamated onto silver wool contained in quartz amalgamation tubes. The wool is then heated and the mercury thus released is flushed by argon into a plasma where it is excited. The emission signal thus produced results in a detection limit of 3 x 10 17 g and an analytical range 1 x 10 14 g-1 x 10"7 g. 

Silver chloride is the oxidized form, so we write it on top of the bracketed fraction, and silver metal is the reduced form, so we write it beneath. But we must also write a term for the chloride ion, because Cl- (aq) appears in the balanced reduction reaction in Equation (7.42). 

Electrochemical oxidation-reduction of eluting mixture components is the basis for amperometric electrochemical detectors. The three electrodes needed for the detection, the working (indicator) electrode, reference electrode, and auxiliary electrode, are either inserted into the flow stream or imbedded in the wall of the flow stream. See Figure 13.13. The indicator electrode is typically glassy carbon, platinum, or gold, the reference electrode a silver-silver chloride electrode, and the auxiliary a stainless steel electrode. Most often, the indicator electrode is polarized to cause oxidation of the mixture components... 

Two methods were used to measure the chlorine leaving-group KIE for the 5n2 reduction of benzyl chloride to toluene by sodium borohydride in DMSO at 30 °C. One procedure involved the classical IRMS technique. The second method was a new technique in which the ratio of the chlorine isotopes was obtained by fast atom bombardment mass spectrometry on silver chloride recovered from the reaction. The KIE values found by the two methods were 1.007 and 1.008, respectively,... 

When two interval scales are used to measure the amount of change in the same property, the proportionality of differences is preserved from one scale to the other. For example. Table 1.4 shows reduction potentials of three electrochemical half-cell reactions measured in volts with reference to the standard hydrogen electrode (SHE, E°) and in millivolts with reference to the standard silver-silver chloride electrode (Ag/AgCl, ). For the SHE potentials the proportion of differences between the intervals +0.54 to +0.80 and +0.34 to +0.80 is... 

There is no historical information in humans to suggest that silver affects reproduction. In an early animal study, there was no reduction in fertility or observable changes in spermatozoa after 2 years of exposure to 89 mg silver/l /day as silver nitrate or silver chloride in the drinking water. 

The reduction of silver chloride, precipitated in the presence of excess chloride ion, yielded the S-shaped curve typical of an autocatalyzed reaction (James, 25). The initial reaction rate, measured in terms of the reciprocal of the time required to complete 5 % of the total reaction, varied directly as the hydroxylamine concentration and inversely as the chloride ion concentration when the latter was relatively large. The specific surface of the freshly prepared precipitate, as measured by dye adsorption, decreased with aging, and the reaction rate decreased proportionately. 

The cyanine dye, 3,3 -diethyl-9-methylthiacarbocyanine chloride, had a much greater effect than gelatin in decreasing the reaction rate of the silver chloride. The rate of reduction of silver chloride varied linearly with the amount of silver chloride surface not covered by the dye, and the rate attained at complete coverage was of the order of one-thousandth that for the undyed precipitate. The dye exerted scarcely any effect upon the reduction of silver ions from silver sulfite complex solution. 

The kinetics of the silver-catalyzed reduction of silver chloride were studied on two types of preparations. In the first the nuclei were... 

Fig. 4. Effect of age of exposure on reduction of silver chloride by hydroxylamine A, no exposure B, exposure 17 hours old C, 6 hours old D, 2 hours old E, 20 minutes old.

The effect of the cyanine dye and of gelatin on the reaction rate shows that reduction of silver ions from solution is not the rate-controlling process. These influences of adsorbed components on the reaction rate speak against the concept that solution of the silver halide is the rate controlling process. Hence, the silver catalyzed reduction of silver chloride by hydroxylamine takes place substantially at the solid silver/ silver halide interface. 

Temperature Coefficients of the Reduction of Silver Chloride by Hydroxylamine... 

Exposure of the silver chloride or bromide to light results in an increase in the nitrogen yield. This is to be expected, because the action of the light supplies nuclei for the catalyzed reaction. On the other hand, exposure of silver thiocyanate, which is relatively insensitive to the action of light, has little or no effect on the amount of nitrogen obtained on subsequent reduction with hydroxylamine. 

The reduction of silver chloride by hydrazine shows some points of similarity to the action of hydroxylamine, but also some important points of difference (James, 34). An induction period was obtained with the unnucleated precipitates which, under some conditions, was relatively large. However, exposure of the precipitate to actinic light had only a small effect upon the induction period and upon the subsequent course of the reaction. Previous nucleation of the precipitate by the action of hydroxylamine decreased the induction period without eliminating it, and produced little or no effect upon the subsequent course of the reaction. Addition of the dye, 3,3 -diethyl-9-methylthiacarbocyanine chloride, produced no effect until the surface of the precipitate was more than half covered. Further increase in the amount of dye added produced an irregular decrease in the reaction rate. Gelatin decreased the reaction rate, but to a smaller extent than in the hydroxylamine reaction, and a minimum rate was not attained. As the gelatin concentration increased, more and more reduced silver appeared in colloidal form in the solution. 

A large part of the reduction of silver chloride by hydrazine evidently takes place by a different mechanism from that of the reduction by hydroxylamine. The effect of gelatin and dye on the process, together with the appearance of colloidal silver in the solution when gelatin is present to stabilize it, shows that the reaction involves dissolved silver chloride to a greater degree than the hydroxylamine reaction. Indeed, if the reaction rate is plotted against a silver ion concentration calculated on the assumption that a saturated solution of silver chloride is maintained, the same relation is obtained as is found for the reduction of silver ions from a solution of the sulfite ion complex. 

The essential difference between the hydroxylamine reaction and the hydrazine reaction appears to be that silver nuclei are formed in the solution much more readily by hydrazine than by hydroxylamine. At sufficiently low pH and in the absence of copper, hydroxylamine does not readily form nuclei in the solution, and the catalytic reduction of the silver chloride occurs essentially at a solid interface with the silver nuclei. Hydrazine, on the other hand, readily forms nuclei in the solution and an important fraction of the total reaction involves the catalytic reduction of dissolved silver chloride. This would account for the well-known photographic properties of the two agents. Hydroxylamine is a cleanworking developer which, under proper conditions, yields little fog. Hydrazine shows much less selectivity and, although it develops an image, it also yields a relatively high fog density. 

The action of an active intermediate oxidation product would explain another feature of the reaction. The reduction of silver ions by hydrazine is extremely sensitive to the presence of small amounts of copper. For example, a solution containing a mixture of silver nitrate, sodium sulfite and hydrazine which normally showed no sign of reduced silver for several minutes underwent almost immediate reaction when merely stirred with a clean copper rod. In the presence of gum arabic as stabilizer, streamers of colloidal silver passed out from the copper surface. Similarly, the addition of small amounts of cupric sulfate to a hydrazine solution eliminated the induction period of the reaction with silver chloride. 

Cupric sulfate exerts an effect on the silver chloride-hydroxylamine reaction similar in kind to that which it exerts on the hydrazine reaction, but in a smaller degree. If sufficient cupric sulfate is added to the hydroxylamine solution, the character of the reduction of silver chloride shifts towards that shown by the hydrazine reaction, e.g., the effect of gelatin becomes less pronounced, a minimum rate at a small gelatin addition is not obtained, and significant amounts of colloidal silver appear in the solution. 

The pH dependence of the rate of development by hydroxylamine indicates that the monovalent ion is the active species. The rate varies as about the 0.65 power of the hydroxylamine concentration at pH 12.7 and the 0.75 power at pH 10.8. These results suggest adsorption of the hydroxylamine ion, and are in complete agreement with previous findings for the catalyzed reduction of silver chloride precipitates. 

The relative rate of fog formation compared to image development increases with increasing pH of the hydroxylamine solution. This is to be expected from analogy with the studies of the reduction of silver chloride and silver bromide precipitates, where the change in nitrogen yield shows that the uncatalyzed reaction becomes more and more prominent as the pH is increased. 

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