7-Lab7-ion- exchange and titration detn Co and Ni

7-Lab7-ion- exchange and titration detn Co and Ni - Chem...

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Chem 223 : Experiment 7 Ion – exchange and Titration Method for the Determination of Cobalt and Nickel References: 1. C, Chaps. 13 (pp. 371-376), 16 (pp. 451-455). 2. H7, Chaps. 19, 23, and 25 3. S & W, Chaps. 15 (especially pp. 443-49), 17 (pp. 487-89). 4. SWH, Chaps. 18, 20 (pp. 505-518), 25 (pp. 652-653), 29 (pp. 715-716). 5. J. S. Fritz & G. H. Schenk, Jr., Quanta. Analyt. Chem., 4th ed., (pp. 582 & 621). 6. J. A. Dalziel and A. K. Slawinski, Talanta 15 , 367-372 (1968). 7. Bjerrum, A. S. Halonin, and L. H. Skibsted, Acta Chem. Scand. 29A, 326-332 (1975). 8. Chem 222. Truman State University The procedure of separation of Co 2+ and Ni 2+ in this experiment is mainly based on the lab. “Spectrophotometric determination of cobalt and nickel” Chem. 223. UIUC I. Purpose of the experiment Determination of multiple components in a single unknown is frequently required. An analyst has a choice of attempting a simultaneous determination or performing a preliminary separation. Each approach has its advantages and drawbacks. Because few techniques are truly specific, any simultaneous determination usually suffers from some mutual interference between the combined components, with resulting loss of accuracy and/or precision. Frequently, however, the resulting uncertainties are less than those introduced by the extra sample handling required for preliminary separation. Furthermore, simultaneous determinations are often faster, and therefore more efficient, than those relying on separations. Generally, the choice of a preferred method must be based on the analyst's assessment of the balance among these factors. In this experiment, the amounts of Co(II) and Ni(II) in a mixture will be determined by two different approaches. First of all, the Co(II) and Ni(II) will be isolated by ion exchange and the separated components assayed. After that Co 2+ will be complexometrically titrated using replacement method and Ni 2+ will be determined by gravimetric analysis. II. Introduction Ion Exchange Chromatography relies on charge-charge interactions between the solutes in your sample and the charges immobilized on the resin of your choice. Ion exchange chromatography can be subdivided into cation exchange chromatography, in which positively charged ions bind to a negatively charged resin; and anion exchange chromatography, in which the binding ions are negative, and the immobilized functional group is positive. Once the solutes are bound, the column is washed to equilibrate it in your starting buffer, which should be of low ionic strength, then the bound molecules are eluted off using a gradient of a second buffer which steadily increases the ionic strength of the eluent solution. Alternatively, the pH of the eluent can be modified as to give your solues or the matrix a charge at which they will not interact and your molecule of interest elutes from the resin. If you know the pH you want to run at and need to decide what type of ion exchange. If it is negatively charged at
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This note was uploaded on 02/13/2011 for the course CHEMISTRY 223 taught by Professor Tathithao during the Spring '10 term at Hanoi University of Technology.

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7-Lab7-ion- exchange and titration detn Co and Ni - Chem...

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