Mercury qualitative analysis

The use of vibrational Raman spectroscopy in qualitative analysis has increased greatly since the introduction of lasers, which have replaced mercury arcs as monochromatic sources. Although a laser Raman spectrometer is more expensive than a typical infrared spectrometer used for qualitative analysis, it does have the advantage that low- and high-wavenumber vibrations can be observed with equal ease whereas in the infrared a different, far-infrared, spectrometer may be required for observations below about 400 cm. ... 

Precipitation reactions have many applications. One is to make compounds. The strategy is to choose starting solutions that form a precipitate of the desired insoluble compound when they are mixed. Then we can separate the insoluble compound from the reaction mixture by filtration. Another application is in chemical analysis. In qualitative analysis—the determination of the substances present in a sample—the formation of a precipitate is used to confirm the identity of certain ions. In quantitative analysis, the aim is to determine the amount of each substance or element present. In particular, in gravimetric analysis, the amount of substance present is determined by measurements of mass. In this application, an insoluble compound is precipitated, the precipitate is filtered off and weighed, and from its mass the amount of a substance in one of the original solutions is calculated (Fig. 1.6). Gravimetric analysis can be used in environmental monitoring to find out how much of a heavy metal ion, such as lead or mercury, is in a sample of water. 

Analytical procedures can be classified in two ways first, in terms of the goal of the analysis, and second, in terms of the nature of the method used. In terms of the goal of the analysis, classification can be based on whether the analysis is qualitative or quantitative. Qualitative analysis is identification. In other words, it is an analysis carried out to determine only the identity of a pure analyte, the identity of an analyte in a matrix, or the identity of several or all components of a mixture. Stated another way, it is an analysis to determine what a material is or what the components of a mixture are. Such an analysis does not report the amount of the substance. If a chemical analysis is carried out and it is reported that there is mercury present in the water in a lake and the quantity of the mercury is not reported, then the analysis was a qualitative analysis. Quantitative analysis, on the other hand, is the analysis of a material for how much of one or more components is present. Such an analysis is undertaken when the identity of the components is already known and when it is important to also know the quantities of these components. It is the determination of the quantities of one or more components present per some quantity of the matrix. For example, the analysis of the soil in your garden that reports the potassium level as 342 parts per million (ppm) would be classified as a quantitative analysis. The major emphasis of this text is on quantitative analysis, although some qualitative applications will be discussed for some techniques. See Workplace Scene 1.1. 

Free Mercury and Mercuric Nitrate.—In absence of lead compounds, free mercury Or -mercuric nitrate may be detected by shaking the vermilion with nitric acid diluted to twice its volume, filtering the solution and treating with hydrogen sulphide in presence of mercury or mercuric nitrate, a black precipitate is obtained. If, however, lead compounds are present, the precipitate should be examined by the ordinary methods of qualitative analysis to ascertain if it contains mercuric sulphide. 

The inorganic compounds in Table 1 include arsenic compounds, cadmium sa1ts lead chloride, lead nitrate, and mercury salts. These are highly poisonous compounds as well as being suspected teratogens, and they need to be handled with extra care. Fortunately, most of these substances are used only in dilute solution and usually in semi-micro quantities. Solutions of arsenic, cadmium, lead, and mercury salts are typically used in connection with Qualitative Analysis procedures, and the amounts used are often no more than a few drops. Hand washing at the end of the laboratory period is especially important after working with solutions such as these. 

The halides of all the metals except silver, lead, mercurous mercury, and cuprous copper are soluble in water, but with the ions of these metals, the halide ions give characteristic precipitates. The precipitates are valuable as tests for identifying either the halogens or the metals in qualitative analysis. 

A. Qualitative Analysis.—Several methods may be employed for the qualitative determination of the platinum metals. The procedure is necessarily varied somewhat according to the nature and number of other metals present. These frequently comprise gold, mercury, arsenic, antimony, and tin. 

The precipitation of mercurous chloride and its change in color from wnite to black on addition of ammonium hydroxide are used as the test for mercurous mercury in qualitative analysis. The effect of ammonium hydroxide is due to the formation of finely divided mercury (black) and mercuric aminochloride (white) by an auto-oxidation-reduction reaction ... 

The most serious defect in the system, especially in its usefulness in the laboratory, is that similar elements are sometimes in remote positions, while dissimilar elements are brought close together. These difficulties are most pronounced in qualitative analysis, in which the solubilities of salts are of prime importance. As illustrations of this defect it may be observed that copper and mercury, silver and thallium, barium and lead, have many similar properties which are not suggested by their positions ixi the table. On the other hand we might expect gold and caesium, rubidium aud silver, and manganese and chlorine to resemble each other much more closely than they do. It is obvious, however, that no table could possibly show all the resemblances and contrasts of each dement, and a, detailed study of each of these elements justifies in a measure its usual position in the table. 

It has been known since the days of alchemy that when Hg2Cl2 is treated with aqueous ammonia a black residue is formed, and this reaction is still used in qualitative analysis to identify Hg2Cl2. Only relatively recently has the nature of the reaction been clarified. These residues contain nitrogen compounds of Hg11 plus metallic mercury, and the Hg11 compounds can be... 

The procedures and principles of qualitative analysis are covered in many introductory chemistry laboratory courses. In qualitative analysis, students learn to analyze mixtures of the common positive and negative ions, separating and confirming the presence of the particular ions in the mixture. One of the first steps in such an analysis is to treat the mixture with hydrochloric acid, which precipitates and removes silver ion, lead(II) ion, and mercury(I) ion from the aqueous mixture as the insoluble chloride salts. Write balanced net ionic equations for the precipitation reactions of these three cations with chloride ion. 

DC polarography dates back almost sixty years to the discovery by Heyrovsky that highly reproducible I-E curves could be obtained using a dropping mercury electrode (DME) as the working electrode. Thus in a polarographic analysis an/-E curve is recorded using a slow linear potential scan and a DME with a droptime of 2—10 s the I-E curve will have the S-shape shown in Fig. 11.13. The half wave potential E l/2 can be used for qualitative analysis since it is a measure of how readily the electroactive species is reduced or oxidized and therefore is a reflection of its molecular structure. In addition, the measurement of the mass-transport-limited current /l can be used for quantitative analysis. 

Chapters 31 through 35 cover the analysis of the groups of cations. (Cations that create serious disposal problems are no longer included in the qualitative analysis chapters. Mercury, silver, lead, and most chromium cations have been removed.) Each chapter includes a discussion of the important oxidation states of the metals, an introduction to the analytical procedures, and comprehensive discussions of the chemistry of each cation group. Detailed laboratory instructions, set off in color, follow. Students are alerted to pitfalls in advance, and alternate confirmatory tests and cleanup procedures are described for troublesome cations. A set of exercises accompanies each chapter. 

Mercury(n) ion is often precipitated as mercury(II) sulfide in qualitative analysis. Using the solubility product constant (Table 18.1), calculate the molar solubility of mercury(II) sulfide in water, assuming that no other reactions occur. 

Many students have prepared coordination compounds in prior chemistry courses but often have not fully understood or even identified them as such. For example, in the Group I qualitative-analysis scheme, lead(II), mercury(I), and silver(I) are isolated as the white precipitates PbCl2, Hg2Cl2, and AgCl, respectively. To separate the silver from the other two cations, aqueous ammonia is added to form the linear diamminesilver(I) complex, [Ag(NH3)2], as shown in Equation (6.1) ... 

The appearance of a dark gray mixture of black mercury and white HgNH2Cl [mercury(II) amidochloride] is the qualitative analysis confirmation of mer-cury(I) ion (see Figure 18-8). 

Mercury vapour in air Diffusive samplers with qualitative onsite colorimetric analysis and quantitative cold vapour atomic absorption spectrometry in the laboratory 59... 

HN03. ICP-AES showed a wide variety of elements to be present with a particular build-up of cobalt, nickel and zinc (50-100 ppm). The presence of lead, cadmium and mercury at dangerously high levels was not indicated. Additional qualitative studies were made by electron probe analysis and ICP-MS. 

Common procedures of qualitative mercury analysis, i.e. using aluminum foil hooked up to a battery to determine the presence of mercury in a solution (mercury metal forms on the surface of the aluminum foil), suggested the use of aluminum as a cathode. This principle was applied on a larger scale using aluminum wire which had to be flattened to a certain thickness for the voltage used. 

Electrolytic deposition was used as a qualitative analytical technique in the early years of current electricity, but it was not until 1864 that quantitative electrochemical analysis commenced with the development of electrogravimetry by Wolcott Gibbs.76,77 Electrolytic techniques of analysis were greatly refined by Edgar Fahs Smith at the University of Pennsylvania, who introduced the rotating anode and double-cup mercury cathode. Smith s book on electrochemical analysis ran to six editions.78... 

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