Exp1, CuCo separation


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13 EXPERIMENT 1 QUANTITATIVE ANALYSIS OF A SOLUTION CONTAINING COBALT AND COPPER PART 1: Separation of Cobalt and Copper by Ion Exchange Chromatography PART 2: EDTA Titration of the Cobalt Solution PART 3: Copper Determination by Atomic Absorption Spectroscopy Reading : Harris, 8 th Ed. , Chapters 11, 20 and 22 Prelab Problems, Harris , 11-6, 11-32, 22-12, 22-18. Write a balanced chemical equation for the back-titration in part 2 of the experiment. For the first week, prepare a flow chart and procedure for part I. Prepare the flowchart and procedure for parts 2&3 as a prelab for the second week of the experiment. T HIS L AB R EQUIRES A F ORMAL W RITTEN R EPORT . GENERAL INTRODUCTION In this experiment, you will be given a solution containing an unknown amount of cobalt and copper. In Part I, you will separate the ions on an anion exchange resin. Once the two elements have been separated, you will analyze for the amount of cobalt by a complex titration in Part II. The copper concentration will be measured by atomic absorption spectroscopy in Part III. PART I: SEPARATION OF COPPER AND COBALT BY ION EXCHANGE A. Introduction Ion exchange resins are insoluble materials that contain cations or anions that can be exchanged. The resins typically consist of a framework held together by strong chemical bonds. Positively or negatively charged functional groups are attached to this framework and each of these groups carries an oppositely charged ion, called a counter ion, which is held by electrostatic attraction. When an ion exchange resin is placed in contact with a solution containing ions, the counter ions on the resin can be replaced by an equivalent number of ions from the solution.
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14 Ion exchange resins are used widely, especially in the biological sciences. In addition to metals, many low molecular weight biochemical compounds, such as amino acids, nucleotides, hormones, peptides, and carboxylic acids, can be separated. Also, ion exchange resins are used as water softeners and deionizers, and to concentrate trace amounts of organic and inorganic compounds. Synthetic ion exchange resins, incorporating various functional groups, are available commercially. Lewis-acidic functional groups are effective as cation exchangers, while Lewis-basic groups exchange anions. The most common resins contain sulfonic acid groups (––SO 3 H + ), which are strongly acidic, or quaternary ammonium groups (––NR 3 + Cl ), which are strong bases. These resins interact with ions in solution by simple exchange reactions: Cation exchange: R––SO 3 H + + M + ! R––SO 3 M + + H + Anion exchange: R'––NR 3 + Cl + X - ! R'––NR 3 + X + Cl The acidic and basic functional groups are attached to organic resins, or polymers, because these materials are easy to synthesize with various functional groups attached. In addition, these organic polymers are insoluble in water and relatively inert. One common cation exchange resin is produced by co-polymerizing styrene and divinylbenzene to give
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This note was uploaded on 01/22/2011 for the course CHEM 4B taught by Professor Moretto during the Spring '09 term at Berkeley.

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