Metal qualitative analysis

In similar circumstances, silver salts leave a residue of metallic silver lead and copper salts usually leave a residue of the corresponding oxide calcium and barium salts leave a resirlne of the carbonate or oxide. Identify the metal in all such cases by the usual tests of qualitative inorganic analysis. Metals other than the above are seldom encountered in elementan qualitative analysis. 

Qualitative Analysis. Nitric acid may be detected by the classical brown-ring test, the copper-turnings test, the reduction of nitrate to ammonia by active metal or alloy, or the nitrogen precipitation test. Nitrous acid or nitrites interfere with most of these tests, but such interference may be eliminated by acidifying with sulfuric acid, adding ammonium sulfate crystals, and evaporating to alow volume. 

Many of the most important naturally occurring minerals and ores of the metallic elements are sulfides (p. 648), and the recovery of metals from these ores is of major importance. Other metal sulfides, though they do not occur in nature, can be synthesized by a variety of preparative methods, and many have important physical or chemical properties which have led to their industrial production. Again, the solubility relations of metal sulfides in aqueous solution form the basis of the most widely used scheme of elementary qualitative analysis. These various more general considerations will be briefly discussed before the systematic structural chemistry of metal sulfides is summarized. 

As shown in Section 2.15, in a solution of 0.25M hydrochloric acid saturated with hydrogen sulphide (this is the solution employed for the precipitation of the sulphides of the Group II metals in qualitative analysis),... 

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. 

Seven chemical reactions were identified from the chemistry syllabus. These chemical reactions were selected because they were frequently encountered during the 2-year chemistiy course and based on their importance in understanding concepts associated with three topics, namely, acids, bases and salts, metal reactivity series and inorganic chemistry qualitative analysis. The seven types of chemical reactions were combustion of reactive metals in air, chemical reactions between dilute acids and reactive metals, neutralisation reactions between strong acids and strong alkalis, neutralisation reactions between dilute acids and metal oxides, chemical reactions between dilute acids and metal carbonates, ionic precipitation reactions and metal ion displacement reactions. Although two of the chemical reactions involved oxidation and reduction, it was decided not to include the concept of redox in this study as students had only recently been introduced to ion-electron... 

Coordinate bonds between metals and ligands result in the formation of complexes under many different types of conditions. In some cases, complexes form in the gas phase, and the number of known solid complexes is enormous. However, it is in solutions that many of the effects of complex formation are so important. For example, in qualitative analysis, AgCl precipitates when a solution of HC1 is added to one containing Ag+. When aqueous ammonia is added, the precipitate dissolves as a result of the formation of a complex,... 

These methods may prove useful in the qualitative analysis of organic compounds, once the selectivities of the precipitants are understood. The metallic oxides suffer from the disadvantage of producing a precipitate which is difficult to filter, while calcite and zirconium phosphates produce relatively well-mannered precipitates. Even when the efficiencies of collection of various model compounds in seawater is known, the immense variety of organic compounds in seawater will keep this technique largely qualitative. 

Polyatomic Organic Molecules. Metal Complexes. Qualitative Analysis - The Identification of Structural Features. Quantitative Analysis - Absorptiometry. Choice of Colorimetric and Spectrophotometric Procedures. Fluorimetry. Applications of UV/Visible Spectrometry and Fluorimetry. 

Hydrogen sulfide causes the precipitation of sulfides from many heavy-metal salts. The classical qualitative analysis scheme depends on precipitation of the sulfides of Hg, Ph, Bi, Cu, Cd, As, Sh, and Sn under acid conditions and the sulfides of Co, Ni, Mn, Zn, and Fe under ammoniacal conditions. 

Qualitative analysis is a procedure for identifying the ions present in an unknown solution. The ions are identified by specific chemical tests, but because one ion can interfere with the test for another, the ions must first be separated. In the traditional scheme of analysis for metal cations, some 20 cations are separated initially into five groups by selective precipitation (Figure 16.17). 

FIGURE 16.17 Flowchart for separation of metal cations in qualitative analysis. 

Detailed procedures for separating and identifying all the ions can be found in general chemistry laboratory manuals. Although modern methods of metal-ion analysis employ sophisticated analytical instruments, qualitative analysis is still included in many general chemistry laboratory courses because it is an excellent vehicle for developing laboratory skills and for learning about acid-base, solubility, and complex-ion equilibria. 

When solutions of soluble ionic compounds are mixed, an insoluble compound will precipitate if the ion product (IP) for the insoluble compound exceeds its fCsp. The IP is defined in the same way as /equilibrium concentrations. Certain metal cations can be separated by selective precipitation of metal sulfides. Selective precipitation is important in qualitative analysis, a procedure for identifying the ions present in an unknown solution. 

The Qualitative Analysis activity in eChapter 16.15 shows the procedure for separating a mixture of metal ions into groups that may be further analyzed to determine the specific ions present. 

Injurious Metals.—These may be derived either from the vessels in which the products are prepared or stored or from mineral colours added to some extent they may be detected in the ash. For a more complete investigation, especially of metals which may be eliminated during the incineration as volatile compounds, use is made of one of the known methods for the destruction of organic substances, e.g., treatment with hydrochloric acid and potassium chlorate, the residue being examined by the ordinary methods of qualitative analysis. 

Ash.—The dry residue from the determination of the water is incinerated and the ash weighed. If this exceeds 1%, adulteration with mineral matter is probable, this being confirmed by qualitative analysis of the ash. Such analysis is useful in any case to detect the presence of heavy metals (especially iron), which may be introduced during the manufacturing processes and are harmful in the dyeing. The ash of alizarin consists normally of sodium or calcium salts. 

Qualitative chemistry is an area of chemistry concerned with identifying substances. In Activity 9.1 you will perform a qualitative analysis to detect the presence of certain ions that, in turn, may reveal an art forgery. The ions could come from paints that were not available at the time of the artwork. In this qualitative analysis, metal ions (cations) and nonmetal ions (anions) are reacted with solvents and with each other. Then the cations and anions present are identified by the products produced. In addition, flame tests and pH determinations are used to identify ions. Qualitative analysis is an engaging opportunity for you to develop experience with chemical change and review solubility principles. Nowadays, however, most of the time a chemist analyzes a substance to detect ion content using quantitative analytical computerized instruments. 

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