221-chapter-27

221-chapter-27 - Gravimetric Analysis Introduction 1...

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Gravimetric Analysis Introduction 1.) Gravimetric Analysis: (i) A technique in which the amount of an analyte in a sample is determined by converting the analyte to some product Mass of product can be easily measured (ii) Analyte : the compound or species to be analyzed in a sample (iii) Overall, gravimetry sounds simple. Advantages - when done correctly is highly accurate (most accurate of all time); requires minimal equipment Disadvantage - requires skilled operator, slow. Convert analyte into a solid, filter, weigh, calculate via a mole map
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Introduction 1.) Gravimetric Analysis: (iii) Example: Determination of lead (Pb +2 ) in water Reagent Analyte Solid Product Gravimetric Analysis
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Gravimetric Analysis Introduction 1.) Gravimetric Analysis: (v) Example: What is the %KCl in a solid if 5.1367 g of solid gives rise to 0.8246 g AgCl?
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Gravimetric Analysis Types of Gravimetric Analysis 1.) Combustion Analysis 2.) Precipitation Combustion Analysis Common method used to determine the amount of carbon and hydrogen One modified method (Dumas Method ) can also determine the amount of nitrogen in a sample Technique is accurate and usable with a wide range of compounds. Often one of the first methods used to characterize a new compound
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Combustion Analysis 1.) Principals: (i) Sample is heated in presence of Oxygen (O 2 ) Converts carbon in sample to CO 2 Converts hydrogen in sample to H 2 O C (sample) + O 2 CO 2 2H (sample) + ½O 2 H 2 O Pt, CuO, PbO 2 , or MnO 2 is used as a catalyst in this process (ii) As CO 2 and H 2 O form, leave the sample and flow through a series of chambers Chambers contain chemicals that bind one or both of these products Example: - P O can be used to absorb H O - Ascarite can be used to absorb CO Gravimetric Analysis Pt Pt Ascarite
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Gravimetric Analysis Combustion Analysis 2.) Apparatus: (i) After the sample is completely burned: Remove P 4 O 10 and Ascarite cartridges and weigh If C and H are present in sample, both cartridges will increase in mass (ii) Amount of C and H in the original sample is determined from: Knowing the amount of sample burned Change in weight in each cartridge
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Combustion Analysis 2.) Example Calculation: A mixture weighing 7.290 mg contained only cyclohexane, C 6 H 12 (FM 84.159), and oxirane, C 2 H
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This note was uploaded on 05/09/2010 for the course CHEM 221 taught by Professor Dr.robertpowers during the Fall '07 term at San Diego.

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221-chapter-27 - Gravimetric Analysis Introduction 1...

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