QualGroupC - Foothill Co llege- Chem istry 1C Name:...

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Foothill College-Chemistry 1C Name: Dr. L.J. Larson 1 Revised/Printed 6/27/08 QualGroupC.doc Separation and Identification of Group C Cations (Ca 2+ , Sr 2+ and Ba 2+ ) Objectives To develop a separation and identification scheme for the Group C cations: calcium, strontium and barium. To complete a flow diagram summarizing the qualitative analysis scheme for the Group B ions. To successfully identify the Group C cation present in an unknown solution. Background Chemistry and Discussion After removing the Group A and Group B cations from your unknown by precipitation, the Group C and D cations remain in solution. The three ions; Ca 2+ , Sr 2+ and Ba 2+ , that make up Group C have soluble chlorides and hydroxides that are reasonably soluble in ammonia solutions. These three ions can be separated from the Group D ions by selective precipitation. Identification of your Group C cation based solely upon the color of the precipitate formed is not possible since the precipitates formed by Ca 2+ , Sr 2+ and Ba 2+ do not have colors unique from each other. Identification can be achieved by using a combination of solubility behavior and flame tests. You are required to develop a scheme that will allow you to separate and correctly identify the Group C cation present in your unknown solution. About Flame Tests When exposed to a flame, certain elements emit light of a characteristic color. As part of our analysis, flame tests of known samples of the Group C cations are necessary in order to become familiar with the characteristic color emitted by each one. Individual known sample solutions can be flame tested directly or the cation can be precipitated and a flame test performed on the precipitate. In either case, a wire loop is used to introduce the sample into the flame The loop of the flame test wire must first be thoroughly cleaned of any trace contamination. Begin by lighting a Bunsen Burner and adjusting the flame so that it burns hot; that is it appears blue, not yellow. Then dip the wire loop in concentrated HCl (in a test tube) and insert the loop into the hottest part of a Bunsen Burner flame; the tip of the inner blue cone. If the wire is contaminated, the flame will exhibit a color characteristic of the contaminant. Repeat the process of dipping the wire loop into the HCl and then inserting it into the flame until no more contamination is apparent. Note that upon sufficient heating the test wire itself will turn the
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This note was uploaded on 09/30/2009 for the course CHEM CHEM 100A taught by Professor Chem100a during the Spring '09 term at UCSD.

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QualGroupC - Foothill Co llege- Chem istry 1C Name:...

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