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Qual%20Scheme%20Lab_student - Your Safer Source for Science...

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Separation and Qualitative Determination of Cations and Anions AP Chemistry Laboratory #14 Catalog No. AP6453 Publication No. 6453A Introduction Much of laboratory chemistry is focused on the question of how much of a given substance is con- tained in a sample. Sometimes, however, the focus shifts to what substances are in the sample, rather than their quantity. In this experiment, an analysis scheme for identifying both cations and anions in solution will be used in determining the ions present in known solutions. Concepts Qualitative analysis Precipitation reactions Background Qualitative analysis is an analytical procedure in which the question “what is present?” is answered. In a systematic qualitative analysis scheme, each substance present is separated from the other substances. Then a confirmatory test is used to prove that the isolated substance is the expected one. To begin the lab experiment, a solution containing four cations is analyzed using the techniques for qualitative analysis of cations. A second solution containing four anions is then analyzed using the qualitative scheme for anions. Two solutions, one containing any combination of four different cations, and another containing any combination of four anions will be assigned to each student group. The two “unknown” solu- tions are then analyzed to determine which ions are present and which are absent. This experiment is carried out on a semi-micro scale. Very small quantities of reagents are used. Cleanliness and a great deal of care are necessary to obtain good results. While going through the steps of the analysis, keep a copy of the appropriate flow chart available for reference. The flow charts appear at the end of the experimental directions. The charts will help to give the “total picture” of where each analysis is and where it is heading. Read the directions IN6453A 121704 CHEM-FAX . . .makes science teaching easier. P.O. Box 219 Batavia, Illinois 60510 1-800-452-1261 [email protected] Visit our website at: www.flinnsci.com © 2003 Flinn Scientific, Inc. All Rights Reserved. Your Safer Source for Science Supplies”
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carefully, and read the sections which give the notes or chemical theory for each step. Don’t just follow directions “cook book” style, but make an effort to understand the chemical principles behind the procedures. General Techniques for Qualitative Analysis Keep Good Records It is necessary to keep good records so as not to get confused and forget what solutions are in which test tubes. Number the test tubes with pencil or permanent ink so the numbers do not come off in the hot water bath. Maintain a current record of the work. Don’t trust the results to your memory. Below is an example from step 1 of the cation analysis.
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