CoComplexesSp05 - Chemis try 135 Clark College Synthesis...

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Chemistry 135 Clark College Cobalt Complexes Spring 2005 NF Page 1 of 6 Synthesis and Characterization of Cobalt Complexes Adapted from “Preparation and Analysis of Two Coordination Complexes of Cobalt”, Carnegie Mellon University. For this experiment: 1. Complete the Prelab and obtain a stamp before you begin the experiment. 2. Write your lab notebook prelab and get it initialed/signed before you begin the experiment. Be sure to summarize the synthetic procedure for your complex. 3. Students whose last names begin with A – Mc will synthesize Complex 1. Students whose last names begin with Me – Y will synthesize Complex 2. You will need to find someone who has synthesized the other complex and share data with them for the Report Sheet. 4. Read the section on filtration in your Laboratory Handbook . 5. Determine the theoretical and percent yield for your synthesis, and report this on the Data Report Sheet. 6. Develop a method using conductivity measurements to determine the chemical formula for the compound you synthesized. Turn in your Data Report Sheet, Stamped Prelab, and notebook pages for this experiment. Introduction In this experiment, you will be synthesizing one of two coordination complexes consisting of cobalt, ammonia and chloride ions. Once you have prepared the complex, you will use conductivity measurements to determine the exact formula of this compound. Finally, you will work with another student and compare results to determine the formula of the other complex. Cobalt, a transition metal, is a rare but important element with a variety of uses. It is found in alloys of steel used as stainless steel and surgical steel. It is also used as a pigment, in magnets, and in industrial catalysts. Biologically, cobalt is found in trace amounts in the complex cobalamin , or Vitamin B12. This complex is part of certain coenzymes used in the synthesis of red and white blood cells and in the normal growth and maintenance of nerve cells. Many transition metals form coordination complexes, which are ionic compounds containing a polyatomic ion that is based around the transition metal ion. The metal ion itself is positively charged and is therefore a Lewis Acid, or an electron pair acceptor. Also, since it is a single-atom ion, the charge of the metal is the same as the oxidation state. Surrounding this metal cation are some number of small molecules or ions called ligands; there are typically 2 – 9 ligands for each metal ion. These ligands are Lewis Bases, and all have a lone pair of electrons that can be donated to the metal ion. Some ligands have multiple atoms with multiple lone pairs, and each atom can attach to the metal. These ligands are called multidentate ligands, from the greek words meaning (loosely) “many teeth”. Several examples of monodentate and multidentate ligands are shown below.
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CoComplexesSp05 - Chemis try 135 Clark College Synthesis...

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