Silver gravimetric analysis

Microwave laboratory ovens are currently quite popular. Where applicable, these greatly shorten drying cycles. For example, slurry samples that require 12 to 16 hours for drying in a conventional oven are reported to be dried within 5 to 6 minutes in a microwave oven. The time needed to dry silver chloride, calcium oxalate, and barium sulfate precipitates for gravimetric analysis is also shortened significantly. ... 

A successful gravimetric analysis consists of a number of important operations designed to obtain a pure and filterable precipitate suitable for weighing. You may wish to precipitate silver chloride from a solution of chloride by adding silver nitrate. There is more to the procedure than simply pouring in silver nitrate solution and then filtering. 

Worked example 6.5 illustrates the use of the common-ion effect in gravimetric analysis AgCl is always precipitated from a solution containing a slight excess of a common ion, CP or Ag , in the determination of silver or chloride respectively. 

The precipitation of chloride and, if present, dissolved bromide and iodide as the total of dissolved halide ions by silver salts as low-solubility silver halides is also not only used for concentrating traces of bromide and iodide for example, but also for gravimetric analysis, as a method of calibration. Bromide and iodide should then be determined separately (Section 3.2) and subtracted from the total of the precipitated halides. Reliable results are then obtained even at high concentrations. 

Specifications, Analysis, and Toxicity. Dicyandiamide is identified quaHtatively by paper chromatography and quantitatively by ultraviolet spectrometry of the chromatogram. More commonly, total nitrogen analysis is used as a purity control or the dicyandiamide is converted by hydrolysis to guanylurea, which is determined gravimetrically as the nickel salt (50). Methods based on the precipitation of silver dicyandiamide picrate are sometimes used (51). Dicyandiamide can also be titrated with tetrabutylammonium hydroxide ia pyridine solution. Table 4 gives a typical analysis of a commercial sample. Dicyandiamide is essentially nontoxic. It may, however, cause dermatitis. 

Caution. Heating, especially to dryness, may result in a violent explosion. For analysis the sample is dissolved in excess 1 N nitric acid at room temperature. Then silver is determined gravimetrically as silver chloride by precipitation with hydrochloric acid. Anal. Calcd. for [Ag(C6H6N)2]C104 Ag, 29.52. Found Ag, 29.39. ... 

Analysis of the compound for platinum is accomplished gravimetrically by reduction of a known weight of the anhydrous salt to metallic platinum with formic acid.3 For the determination of chloride, 0.3 g. of the anhydrous salt is dissolved in 40 ml. of distilled water containing 250 mg. of hydrazine sulfate the solution is boiled gently until platinum metal is formed and coagulated. Then, without removal of the platinum, the solution is made 1 f in nitric acid and is titrated potentiometrically with standard 0.2 F silver nitrate solution. Anal. Calcd. for Na2PtCl6 Pt, 42.99 Cl, 46.88. Found Pt, 42.78 Cl, 46.73. 

The analysis of simple fulminate-chlorate mixtures may be effected by extraction either with water or with pyridine. In the former method the mixture ts digested with c

mercury fulminate is dried at 50 for three hours and weighed. Some fulminate dissolves in the water. This is estimated by precipitation as sulphide. The chlorate may also be determined in the filtrate. The solution t boiled with nitric acid and tlwn treated with fbrntaldehyde and silver nitrate. Silver chloride is precipitated and the estimation may be made gravimetrically or by Vol hard s method. 

Argentiometric procedures cut across the classification boundaries to some extent, in that volumetric, gravimetric or colorimetric methods may be applied to the analysis of particular silver salts. However, the argentiometric methods for the determination of phosgene are specific to the chloride ion, and as such are susceptible to other chloride impurities (especially dichlorine or hydrogen chloride). The details of these methods have been reviewed elsewhere [1255], and since they are neither specific to phosgene, nor in any obvious way amenable to automation, they will not be reviewed here. 

For the analysis of rhenium, the sample is fused with sodium peroxide and rhenium precipitated from hydrochloric acid solution as Re2S7 by hydrogen sulfide. The precipitate is dissolved in aqueous sodium peroxide and from dilute sulfuric acid solution, rhenium is determined by electrodeposition.8 Chlorine is determined gravimetrically by fusion of the sample with a sodium carbonate/ sodium nitrate mixture (95 5) in a platinum crucible and then precipitating as silver chloride. 

Analytical chemistry began in the late eighteenth century with the work of French chemist Antoine-Laurent Lavoisier and others the discipline was further developed in the nineteenth century by Carl Fresenius and Karl Friedrich Mohr. As a pharmacist s apprentice in Frankfurt, Germany, Fresenius developed an extensive qualitative analysis scheme that, when it was later published, served as the first textbook of analytical chemistry. He built a laboratory at his house that opened in 1848. Here he trained students in gravimetric techniques that he had developed. Mohr developed laboratory devices such as the pinch clamp burette and the volumetric pipette. He also devised a colorimetric endpoint for silver titrations. It was his 1855 book on titrimetry, Lehrhuch der Chemisch-Analytischen Titromethode, that generated widespread interest in the technique. 

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