Qualitative cation analysis described

Describe how to use precipitation, acid-base, redox, and complex ion formation reactions in qualitative cation analysis. 

Briefly describe each of the following ideas, methods, or phenomena (a) common-ion effect in solubility equilibrium (b) fractional precipitation (c) ion-pair formation (d) qualitative cation analysis. 

The book begins with a discussion of the basic physico-chemical aspects of reactions utilised in qualitative inorganic analysis. A description of laboratory equipment follows, and operations which include semimicro and micro techniques, and simple electrochemical, spectroscopic and chromatographic methods. The reactions of the most important cations and anions are described, followed by a treatment of systematic qualitative analysis. Sample preparation, dissolution and fusion of insoluble materials are treated in detail. A separate chapter deals with the reactions of less common ions, with guidelines to their separation and identification in the course of systematic analysis. Finally, a simplified course of qualitative analysis is given this chapter will be particularly useful where the time allocated to qualitative analysis is limited. 

II.l INTRODUCTION Before the student attempts to carry out the analytical reactions of the various cations and anions detailed in Chapters III and IV, he should be familiar with the operations commonly employed in qualitative analysis, that is with the laboratory technique involved. It is assumed that the student has had some training in elementary practical chemistry he should be familiar with such operations as solution, evaporation, crystallization, distillation, precipitation, filtration, decantation, bending of glass tubes, preparation of ignition tubes, boring of corks, and construction of a wash bottle. These will therefore be either very briefly discussed or not described at all in the following pages. 

The qualitative analysis scheme for cations based on the selective precipitation procedure described above is summarized in Fig. 8.13. 

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. 

In the Cambridge International AS and A Level Advanced Practical Skills examination (Paper 3), you will need to follow instructions to carry out an investigation into an unknown substance or mixture of substances. Always read through all of the instructions before carrying out the tests. Testing for unknown substances will require you to describe your observations in detail. You will be able to refer to tables of tests for cations, anions and gases in the Qualitative Analysis Notes in your examination paper (see Appendix 3, page 475) to draw your conclusions. 

Thorough characterization of commercial products requires determination of the anion associated with the cationic surfactant as well as determination of other salts present. Determination of chloride and sulfate ions is described in Chapter 1. These and other anions are usually determined by ion chromatography, although wet chemical methods may also be applied after qualitative analysis has shown which ions are present. 

Konig and Waldorf discuss analysis of hair and body shampoos (32). The shampoo is first evaporated to dryness and extracted with isopropanol or 95% ethanol to separate the surfactant, which is qualitatively identified by IR. The alcohol-insoluble residue is also examined by IR in case a less-soluble surfactant remains there. The alcohol extract is then separated into anionic, cationic, nonionic, and amphoteric surfactant fractions by ion exchange. Anionics can be separated into sulfonates and carboxylates by use of strongly basic anion exchange resins in the Cl" and OH" form, respectively. Anionics are further characterized by TLC. Nonionics are likewise characterized by TLC. Once the components are identified, quantitative analysis is by the usual methods, described elsewhere in this volume. 

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