Analysis, chemical qualitative

Selective precipitation as discussed in Section 16.6 can be used in a systematic way to determine which metal ions are present in an unknown solution. This method is known as qualitative analysis. The word qualitative means involving quality or kind. Qualitative analysis involves finding the kind of ions present in the solution. This stands in contrast to quantitative analysis, which is concerned with quantity, or the amounts of substances in a solution or mixture. 

In the past, qualitative analysis by selective precipitation was used extensively to determine the metals present in a sample. This process—dubbed wet chemistry because it involves the mixing of many aqueous solutions in the lab—has been replaced by more precise and less time-intensive instrumental techniques. Nonetheless, both for the sake of history and also because of the importance of the principles involved, we now examine a traditional qualitative analysis scheme. You may use such a scheme in your general chemistry laboratory as an exercise in qualitative analysis. 

A FIGURE 16.15 Qualitative Analysis In qualitative analysis, specific ions are precipitated successively by the addition of appropriate reagents. 

Early methods of distinguishing between the so-called ortho, meta and pyro phosphates were based on the reactions obtained with neutral silver nitrate solution and with egg albumin (Table 14.1). 

In subsequent schemes of qualitative analysis, orthophosphates, obtained in Group III separations, were distinguished from pyro and the so-called metaphosphates by the ammonium molybdate test. 

If a solution of ammonium molybdate in concentrated nitric acid is added in excess to an orthophosphate solution, a yellow precipitate of ammonium phosphomolybdate is obtained in the cold or with very slight warming (1). No reaction is obtained from pyro or metaphosphates under the same conditions, but, if they are heated, hydrolysis will occur and orthophosphates will be detected. 

H3PO4 -E 12(NH4)2Mo04 + 2IHNO3 (NH4)3PMo,2O40 + 2INH4NO3 -T I2H2O (14.1) 

Unless removed by prior treatment, orthoarsenates can also give a similar precipitate of (NH4)3AsMo,204o. This early method of distinguishing orthophosphates from other phosphates was based on an oversimplified classification of condensed phosphates (Chapter 5.4). All of these compounds can, however, be hydrolysed in acid solution and thus eventually be detected and estimated as orthophosphate. 

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Electrochemical phenomena and processes are nsefnl for the qnantitative and qualitative chemical analysis of varions snbstances and media, inclnding liquids, gases, and solids. The high accnracy of the electrochemical methods of analysis derives from the fact that they are based on highly exact laws (e.g., those of Faraday). 

The above conclusion is confirmed by experiments were ethylene was led into the vial with an antimony film treated by hydrogen atoms. This experiment provides an example of a qualitative chemical analysis of atom hydrogen. In is known [21] that capturing of hydrogen atoms by molecules of ethylene develops with high rate resulting in creation of... 

The first steps in unravelling the details of an unknown system frequently involve the identification of its constituents by qualitative chemical analysis. Follow-up investigations usually require structural information and quantitative measurements. This pattern appears in such diverse areas as the formulation of new drugs, the examination of meteorites, and studies on the results of heavy ion bombardment by nuclear physicists. 

Vogel, A. I. (1937). A Text-book of Qualitative Chemical Analysis. London, Longmans, Green and Co. 

References Textbooks on advanced general chemistry or on physical chemistry Stieglitz, Qualitative Chemical Analysis, Part I, p. 139 (1925). 

For inorganic substances, chemical reactions may be carried out on a small scale on microscope slides, the crystallization of reaction products being watched. Tests for particular ions or atom groups have been devised, the criterion of identity being, not solubility or colour, as in macroscopic qualitative chemical analysis, but crystallographic properties. For information on such methods, see Handbook of Chemical Microscopy, by Chamot and Mason (1958). 

In the interest of putting modern analytical chemistry in perspective, it is in order to review that long time period (essentially prior to the 1940s) when the subject was divided into two readily understood areas 1. Qualitative chemical analysis, in which one is concerned simply with the identification of die constituents of a compound or components of a mixture, sometimes accompanied by observations (rough estimates) of whether certain ingredients may be present in major or (race proportions. 

The XPS mechanism, which can be used for quantitative and qualitative chemical analysis of surfaces, is based on the photoelectric effect. A monochromatic soft Mg or Al anode X-ray source is used to irradiate the surface. The absorbed X-rays ionize die core shell, and in response, the atom creates a photoelectron that is transported to the surface and escapes. The ionization potential of a photoelectron that must be overcome to escape into vacuum is the binding energy (BE) plus the work function of the material. The emitted photoelectrons have a remaining kinetic energy (KE), which is measured by using an electron analyzer. Individual elements can be identified on the basis of their BE. The resulting XP spectrum is a characteristic set of peaks for a specific element, with BE as the abscissa and counts per unit time as... 

The branch of chemistry that deals with the identification of elements or grouping of elements present in a sample is called qualitative chemical analysis, or qualitative analysis for short. It does not deal with anything to do with quantities. 

Line spectra were first observed by J. von Fraunhofer, D. Brewster, and J. F. W. Herschel in the 1820s.180 In the ensuing decades a considerable amount of work was done on spectral phenomena prior to the demonstration by Bunsen and Kirchhoff in 1859 that line spectra could be used for qualitative chemical analysis. Accounts have appeared of the development of the spectroscope both prior and post Bunsen and Kirchhoff.181-183 Significant observations were undoubtedly made prior to 1860 by Stokes, Stewart, Fox Talbot, and others. The priority claims of Stokes, who recorded his ideas in some private letters to William Thomson, have been examined.184 The work of Bunsen and Kirchhoff did not owe a great deal to that of their predecessors, with the exception of the demonstration by W. Swan in 1856 that the almost omnipresent yellow line that coincided with Fraunhofer s dark solar D line was due to contamination by minute quantities of sodium salts.185 186 Platinum played an important role in the early development of spectroscopy. The metal was widely used to support the material in the flame, since it did not colour the flame itself. Bunsen ensured the purity of all his samples for spectrum analysis by recrystallization (sometimes up to fourteen times) in platinum vessels, thereby preventing contamination by minute quantities of salts that could be leached from glass vessels.187 Sharply contrasting views have been expressed about the failure of chemists prior to Bunsen to exploit spectroscopy.188-190... 

First Published under the title A Text-book of Qualitative Chemical Analysis 1937 Second Edition 1941 Reissue with Appendix 1943 Third Edition under the title A Text-book of Qualitative Chemical Analysis including Semimicro Qualitative Analysis 1945 Fourth Edition under the title A Text-book of Macro and Semimicro Qualitative Inorganic Analysis 1954... 

First-3d ed. published under title A text-book of qualitative chemical analysis 4th ed. published under title A text-book of macro and semimicro qualitative inorganic analysis. 

Craft s Short Course in (Qualitative Chemical Analysis. (Schaeffer.).zamo, a 00... 

Manual of Qualitative Chemical Analysis. Paitl. Descriptive. (Wells.)... 

A.LVogcl, A textbook of qualitative chemical analysis. Longmans,Green and co, London. 

Profile The company develops, manufactures, and sells mass spectrometers, liquid chromatographs, and gas chromatographs for the environmental, pharmaceutical, and industrial marketplaces. These analytical instruments are used in the quantitative and qualitative chemical analysis of organic and inorganic compounds at ultratrace levels of detection. ThermoQuest is a public subsidiary of Thermo Instrument Systems, Inc. (AMEX THI), a Thermo Electron (NYSE TMO) company. 

Although most people, in their everyday lives, do not perform the types of experiments and procedures associated with qualitative chemical analysis, the results and benefits of qualitative analysis have a tremendous impact in common experience. 

An Introduction to Qualitative Chemical Analysis and the Related Chemical Principles... 

First published under the title A Text-book of Qualitative Chemical Analysis 1937 Second edition 1941 Reissue with Appendix 1943... 

Third edition under the title A Text-hook of Qualitative Chemical Analysis including Semimicro Qualitative Analysis 1945... 

This exercise has introduced selected principles of molecular UV and infrared spectroscopy for qualitative chemical analysis. Interpret the significance of these spectra in terms of molecular structure. You should have obtained hardcopy printouts of UV and FTIR spectra. Please include all relevant spectra in your report. 

Valcarcel M, Cardenas S, Barcelo D, Buydens L, Heydorn K, Karlberg B, Klemm K, Lendl B, Milman B, Neidhart B, Rios A, Stephany R, Townshend A, and Zschunke A (2002) Metrology of Qualitative Chemical Analysis. EUR 20605 EN, European Commission, Brussels. Zolotov YA, Ivanov VM, and Amelin VG (2002) Chemical test methods of analysis. In Barcelo D (ed.) Comprehensive Analytical Chemistry, vol. XXXVI. Amsterdam Elsevier. 

Both types of problems are common in the different branches of Chemistry. For example, in Qualitative Chemical Analysis one is frequently faced with a solution containing several unknown cations and anions. The analyst must carry out a pre-established series of reactions, and according to the results must rule out or confirm the presence or absence of the more usual cations and anions. This procedure allows the analyst, depending on the results (formation of precipitates, turbidity, colour reactions in the solution, etc.), to deduce the composition of the problem sample. Qearly, this is an example of a causation problem, because the procedure is pre-established, the results are in plain view and the objective is to know what solution composition is compatible with the results obtained (Martinez-Luaces, 2011). 

See R. K. McAlpine and B. A. Soule, Qualitative Chemical Analysis, van Nostrand, New York,... 

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