Separation and Identification of Group C Cations - Foothill College

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Foothill College-Chemistry 1C Reagents Available Qualitative Analysis Group C 1-M (NH 4 ) 2 SO 4 1-M (NH 4 ) 2 CO 3 Saturated Ammonium Oxalate solution Concentrated HCl 6-M NaOH 6-M NH 3 Concentrated HNO 3 6-M acetic acid (CH 3 COOH) Dilute, Known Solutions of Ca 2+ , Sr 2+ and Ba 2+ Safety and Waste Disposal Some of Group C cations are toxic. The HCl, HNO 3 and NaOH are irritants. Avoid contact and wash immediately if any is spilled or splashed on you. Wear eye protection at all times. As you perform the experiment, collect all waste solutions in a waste beaker. This mixture should then be discarded in the appropriate waste container. DO NOT POUR ANY OF THE SOLUTIONS DOWN THE DRAIN. Unknowns and Knowns Separate known samples containing Ca 2+ , Sr 2+ and Ba 2+ are provided for your use. Testing known samples is helpful in this analysis since doing so will allow you to observe what a positive test looks like. The known Group C samples are best tested separate from each other. To prepare a known sample for testing, add 2 to 3 drops of the solution containing the cation you wish to test to about 0.5 mL of water. Remember that experimental conditions, such as pH, for the known tests must be the same as that for the unknown. Outline of Procedure: Use the template given below for a written summary of your proposed procedure and use a flow diagram in your notebook to record all observations for each step in your procedure. Part of your procedure should include flame tests of the known samples. It is likely that your initial procedure will need to be modified, depending on your results in lab, as you progress through the analysis. Chemistry and Relevant Background Information: Experimental Procedure: Dr. L.J. Larson 2 June 27, 2008 QualGroupC.doc
Foothill College-Chemistry 1C Prelab Exercise: 1. Explain why flame tests are necessary in the Group C analysis. Name: Qualitative Analysis Group C 2. To help you determine a proposed separation and identification scheme for the Group C cations, answer the following questions: a) Refering to Table 2 in the Introduction to Qualitative Analysis, list K sp values for the hydroxide, oxalate, sulfate and carbonate salts of the Group C cations. Organize your values in table form below. b) Now study the solubilites of the Group D cations, referring again to Table 2 of the Introduction to Qualitative Analysis. Which of the anion(s) listed in part (a) could possibly be used to selectively precipitate the Group C cations while leaving the Group D cations in solution? c) Now write the solubility rule given for sulfates in Table 3 of the Introduction to Qualitative Analysis. d) Now write the solubility rule given for oxalates in Table 3 of the Introduction to Qualitative Analysis. Dr. L.J. Larson 3 June 27, 2008 QualGroupC.doc
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Separation and Identification of Group C Cations - Foothill College

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