Determination silver

The fire assay, the antecedents of which date to ancient Egypt, remains the most rehable method for the accurate quantitative determination of precious metals ia any mixture for concentrations from 5 ppm to 100%. A sample is folded iato silver-free lead foil cones, which are placed ia bone-ash cupels (cups) and heated to between 1000 and 1200°C to oxidize the noimoble metals. The oxides are then absorbed iato a bone-ash cupel (ca 99%) and a shiny, uniformly metaUic-colored bead remains. The bead is bmshed clean, roUed fiat, and treated with CP grade nitric acid to dissolve the silver. The presence of trace metals ia that solution is then determined by iastmmental techniques and the purity of the silver determined by difference. 

This reaction is also used in the method of Holleman 2 as modified by Wilkie.3 A phosphate solution containing phenolphthalein is reddened by the addition of alkali, then just decolorised with nitric acid. An excess of standard silver nitrate is then added and decinormal sodium acetate and alkali to slight pink colour, followed by 2 c.c. of decinormal H2S04. The solution is diluted and filtered and the excess of silver determined by titration with decinormal ammonium thiocyanate. 

All halides, except fluoride, interfere in the determination of silver. An approximately equimolar amount of chloride can be tolerated. In certain cases, large amounts of chloride or bromide may be used to mask silver in the determination of other noble metals with TMK. Thiosulphate, thiocyanate, sulphide, phosphate, as well as redueing and oxidizing agents interfere in the silver determination. 

A product of sufficient purity for use in the oxidation reactions mentioned above may be prepared by dissolving 170 g. (1 mol) of silver nitrate and 106 g. (1 mol) of sodium chlorate each in 100 ml. of water. After the two solutions are heated to 85°, they are mixed and allowed to cool slowly to 0°, and at this temperature the mother liquor is carefully decanted. Fifty milliliters of distUled water, previously cooled to 0°, is added to the solid product, and the crystals are separated by suction filtration. Yield 150 g. (78.5 per cent). The product contains 95.2 per cent AgClOs as indicated by a silver determination. 

Figure 7.31 Orientation and structure of nicotinic acid on silver determined by surface-enhanced Raman spectroscopy, (a) Flat orientation, pH < 9, (b) perpendicular orientation, pH > 9, and (c) alternative perpendicular orientation (not observed). ...

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Silver determination with the graphite tube technique (Furnace method)... 

Theophylline behaves analytically like theobromine. It can be quantitatively methylated to caffeine by the method of Self and Rankin given above and it forms an insoluble silver compound. However, sodium acetate is sometimes present and will interfere with the silver determination unless the acetic acid is volatilised with excess of standard sulphuric acid. 

A resistor is colour coded green, blue, brown, silver. Determine the value of the resistor. 

The following figure shows a plot of the loga-Q rithm (to the base 10) of the diffusion coefficient versus reciprocal of the absolute temperature for the diffusion of gold in silver. Determine values for the activation energy and preexponential. 

Flame atomic absorption spectrometry (FAAS) is proposed to determine silver nitrate (by means of silver determination), selenium disulphide (by means of selenium determination) zirconium and aluminium. Zinc is determined gravimetrically. 

Sewage effluents, determination of, organic compounds 135-137,194, 207,226,261,262,353-362,462, 463 organometallic compounds 265, 266 Silicate, determination of 213 Silver, determination of 205, 206 Size exclusion high performance liquid chromatography, applications of 216-221 determination of, anions 218-220 cations 217, 218 organic compounds 216,217 Sodium, determination of 205, 206,... 

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