Lecture 7 - Lecture 7 Gravimetry and Ion Exchange...

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Anal Chem 251 Lecture 7 Gravimetry and Anion Exchange Chromatography 1 Chapter 7 Gravimetric and Combustion Analysis (Problems 7:3,6,7,13) Chapter 23 pp . 499-502 Ion-Exchange Chromatography Lecture 7 Gravimetry and Ion – Exchange Chromatography Corresponding Lab: Determination of Cl - , SO 4 2- , Gravimetry and Anion Exchange Chromatography
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Anal Chem 251 Lecture 7 Gravimetry and Anion Exchange Chromatography 2 Gravimetric Methods • Gravimetric Methods are quantitative methods that are based on determining the mass of a pure compound to which the analyte is chemically related. • In precipitation gravimetry , the analyte is separated from a solution of the sample as a precipitate, and is converted to a compound of known composition that can be weighed.
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Anal Chem 251 Lecture 7 Gravimetry and Anion Exchange Chromatography 3 Lab Experiment: Gravimetric Analysis of Chloride and Sulfate Seawater Chloride Ion is the principal anion in seawater. In the lab, one way of separating Cl - and SO 4 2- is by selective precipitation of Cl. Note: There are two ways of removing sulfate, anion exchange and selective precipitationof BaSO 4 . We will determine the chloride concentration in seawater by a gravimetric procedure through selective precipitation of Cl-. Cl - (aq) + Ag + (aq) AgCl (s) K sp = 1.82 x 10 -10 ( Ag+ from AgNO 3 ) By using stoichiometry, measuring the mass of AgCl (s) leads to the mass of Cl - . The addition of excess silver ion, Ag + (aq), to a solution containing Cl - (aq) causes the precipitation of silver chloride, AgCl (s) which is then filtered, dried and weighed.
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Anal Chem 251 Lecture 7 Gravimetry and Anion Exchange Chromatography 4 Lab Experiment: Gravimetric Analysis of Chloride and Sulfate Seawater (Continued) • Sulfate ion in seawater is measured by adding a solution of barium nitrate that causes the selective precipitation of BaSO 4 (s). By filtering, drying, and weighing the barium sulfate precipitate, we will measure the sulfate concentration. SO 4 2- (aq) + Ba 2+ (aq) BaSO 4 (s) • By using stoichiometry, measuring the mass of BaSO 4 (s) leads to the mass of SO 4 2-
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Anal Chem 251 Lecture 7 Gravimetry and Anion Exchange Chromatography 5 Properties of Precipitates and Precipitating Reagents •A g + (aq) and Ba 2+ (aq) in our lab experiment are gravimetric precipitating reagents . Ideally, a gravimetric precipitating reagent convert the analyte to a sparingly soluble precipitate. The precipitating reagent should react specifically or at least selectively with the analyte. Specific reagents , which are rare, react only with a single chemical species. Selective reagents , which are more common, react with
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Anal Chem 251 Lecture 7 Gravimetry and Anion Exchange Chromatography 6 Properties of Precipitates and Precipitating Reagents (Continued) In addition to specificity and selectivity, the ideal precipitating reagent would react with the analyte to give a product that is: 1. Easily filtered and washed free of contaminants
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This note was uploaded on 04/27/2008 for the course CHEM 251 taught by Professor Vassilian during the Fall '06 term at Rutgers.

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Lecture 7 - Lecture 7 Gravimetry and Ion Exchange...

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