Silver chloride method

Silver chloride is reduced to the metal by zinc. One of the methods of recovering silver from silver residues depends on this. The residue is first treated with concentrated hydrochloric acid and then sulphuric acid and zinc added ... 

Qualitative. The classic method for the quaUtative determination of silver ia solution is precipitation as silver chloride with dilute nitric acid and chloride ion. The silver chloride can be differentiated from lead or mercurous chlorides, which also may precipitate, by the fact that lead chloride is soluble ia hot water but not ia ammonium hydroxide, whereas mercurous chloride turns black ia ammonium hydroxide. Silver chloride dissolves ia ammonium hydroxide because of the formation of soluble silver—ammonia complexes. A number of selective spot tests (24) iaclude reactions with /)-dimethy1amino-henz1idenerhodanine, ceric ammonium nitrate, or bromopyrogaHol red [16574-43-9]. Silver is detected by x-ray fluorescence and arc-emission spectrometry. Two sensitive arc-emission lines for silver occur at 328.1 and 338.3 nm. 

It is therefore necessary to remove the silver chloride by filtration. The filtration may be avoided by the addition of a little nitrobenzene (about 1 mL for each 0.05 g of chloride) the silver chloride particles are probably surrounded by a film of nitrobenzene. Another method, applicable to chlorides, in which filtration of the silver chloride is unnecessary, is to employ tartrazine as indicator (Section 10.82). 

Note on the gravimetric standardisation of hydrochloric acid. The gravimetric standardisation of hydrochloric acid by precipitation as silver chloride is a convenient and accurate method, which has the additional advantage of being independent of the purity of any primary standard (compare Section 10.38). Measure out from a burette 30-40mL of the, say, 0.1M hydrochloric acid which is to be standardised. Dilute to 150 mL, precipitate (but omit the addition of nitric acid), and weigh the silver chloride. From the weight of the precipitate, calculate the chloride concentration of the solution, and thence the concentration of the hydrochloric acid. 

A second method which is now probably the most widely used method in the Pediatric Laboratory is to use amperometric titration. In this connection, a constant current flows through the solution. The silver dissolves and reacts stolchlometrlcally with chloride, precipitating silver chloride. When all of the chloride has reacted, there is a sharp increase in conductivity which is read as an end point. This instrument, therefore, measures the amount of time a current flows. Instruments are now available for which 5 microliters can be used routinely, rapidly, titration being of the order of about 20 seconds. 

A third method for chloride estimation which is commonly employed is the silver-silver chloride electrode. In this method the solution is usually diluted in a buffer, and the voltage generated measured. The problem with this procedure is that the electrode needs to be carefully maintained or problems occur. With larger volumes the chloride electrode has been very successful. 

The chlorides of most metals have a very good water solubility, though there are exceptions in the case of some metals. A typical example of the latter is silver which can be very efficiently separated by forming insoluble silver chlorides. Although, the separation of silver as the chloride is rarely used as a method for bulk precipitation, it is certainly useful for the removal of relatively small amounts of the metal when present as a minor constituent In the case of cuprous and cupric chlorides, the former has a low solubility in water hence, if the leach liquor contains cupric chloride, a suitable reducing agent such as sulfur dioxide can be introduced to convert cupric chloride to cuprous chloride so that precipitation occurs. 

Exposure of ammoniacal silver chloride solutions to air or heat produces a black crystalline deposit of fulminating silver , mainly silver nitride, with silver diimide and silver amide also possibly present [1], Attention is drawn [2] to the possible explosion hazard in a method of recovering silver from the chloride by passing an ammoniacal solution of the chloride through an ion exchange column to separate the Ag(NH3)+ ion, prior to elution as the nitrate [3], It is essential to avoid letting the ammoniacal solution stand for several hours, either alone or on the column [2], See Silver nitride... 

In the Nile blue spectrophotometric method, 10 ml 2% aqueous hydrofluoric acid is added to a 10 ml sample contained in a polyethylene bottle. The mixture is shaken for about 2h. Aqueous ferrous sulfate 10% 10 ml and 1ml 0.1% aqueous Nile blue A are added, then extracted with o-dichlorobenzene (10 ml and 3x5 ml). The combined organic extracts are diluted to 50 ml with the solvent and the extinction measured at 647 nm. Interference from chloride ions up to 100 mg/1 can be eliminated by precipitation as silver chloride. 

Also, the addition of silver sulfate causes precipitation of silver chloride, which in the presence of organic compounds is neither completely nor reproducibly oxidised. This method, whilst being applicable to estuarine waters of relatively low chloride content, would present difficulties when applied to highly saline estuarine and sea waters of low organic content. 

In Nebraska, state regulations require that the chemical makeup of animal feed sold in the state be accurately reflected on the labels found on the feed bags. The Nebraska State Agriculture Laboratory is charged with the task of performing the analytical laboratory work required. An example is salt (sodium chloride) content. The method used to analyze the feed for sodium chloride involves a potentio-metric titration. A chloride ion-selective electrode in combination with a saturated calomel reference electrode is used. After dissolving the feed sample, the chloride is titrated with a silver nitrate standard solution. The reaction involves the formation of the insoluble precipitate silver chloride. The electrode monitors the decrease in the chloride concentration as the titration proceeds, ultimately detecting the end point (when the chloride ion concentration is zero). 

The preparation of dichloroacetone by the following methods is described in the literature the direct chlorination of acetone 1 the oxidation of dichlorohydrin 2 the action of silver chloride on diiodoacetone 3 the action of dichloropropene (CH2CI— CC1 = CH2) and hypochlorous acid 4 the action of hydrochloric acid on ethoxymonochloroacetoacetic ester 5 and the hydrolytic cleavage of dichloroacetoacetic ester.6... 

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,... 

The construction and preparation of these electrodes were described in chapter 3.1. The modern version of this electrode, produced by Radelkis, Budapest, is a compromise between the original construction described by Pungor etal. [310,311, 313] and a system with a compact membrane. Electrodes with silver chloride, bromide and iodide are manufactured. According to the manufacturer these electrodes should be soaked before use for 1-2 hours in a dilute solution of the corresponding silver halide. They can be used in a pH region from 2 to 12 and the dFisE/d log [X ] value is approximately 56mV. These electrodes can be employed for various automatic analytical methods (see chapter 5). They can readily be used in mixtures of alcohol with water, for example up to 90% ethanol and methanol and up to 4% n-propanol and isopropanol [196]. In mixtures of acetone-water and dimethylformamide-water, they work reliably only in the presence of a large excess of water [197]. 

Lead in water may he analyzed very precisely at low concentrations hy anodic stripping voltametry using an electrochemical analyzer static or controlled growth mercury drop electrodes, reference calomel or silver-silver chloride electrodes and silica or TEE cells. Copper, silver, gold, and certain organic compounds may interfere in the test. (APHA, AWWA and WEE. 1998. Standard Methods for the Examination of Water and Wastewater, 20 ed. Washington, D.C. American Public Health Association.)... 

The purity of the crystallized product, determined volu-metrically by Volhard s method, exceeds 98%. In this procedure, 10 ml. of a 1% solution of methylisourea hydrochloride is acidified with a few drops of nitric acid and treated with 20 ml. of 0.1 N silver nitrate. After removal of the silver chloride by filtration, the excess of the silver nitrate is estimated with 0.1 TV thiocyanate solution, using ferric alum as indicator. Alternatively, 10-ml. portions of 0.1 N silver nitrate, acidified with nitric acid, may be titrated directly with the 1% methylisourea hydrochloride solution in the presence of tartrazine. 

The silver chlorine ratio was determined by E. Turner (1829),4 F. Penny (1839), J. C. G. de Marignac (1842), J. B. A. Dumas (1860), J. S. Stas (1865), and by T. W. Richards and R. C. Wells (1905) by the precipitation of silver chloride. L. Maumene reduced silver chloride to the metal by heating it in a stream of hydrogen and J. S. Stas also synthesized silver chloride by heating the metal in chlorine gas. This ratio has also been determined by several less direct methods. F. W. Clarke s calculations furnished 32 8606 0 00031 for the general mean representing the amount of chlorine which combines with 100 parts of silver to form silver chloride. 

In aqueous solutions, the method of measuring electrode potentials has been well established. The standard hydrogen electrode (SHE) is the primary reference electrode and its potential is defined as zero at all temperatures. Practical measurements employ reference electrodes that are easy to use, the most popular ones being a silver-silver chloride electrode and a saturated calomel electrode (Table 5.4). The magnitude of the liquid junction potential (LJP) between two aqueous electrolyte solutions can be estimated by the Henderson equation. However, it is usual to keep the LJP small either by adding the same indifferent electrolyte in the two solutions or by inserting an appropriate salt bridge between the two solutions. 

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