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6-Gravimetric Analysis

6-Gravimetric Analysis - Chapter 27 Gravimetric Methods of...

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Chapter 27 - Gravimetric Methods of Analysis Gravimetric methods of analysis are one of the most accurate and precise methods for macro- quantitative analysis. Gravimetries are quite tedious but very useful!
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Chapter 27 - Gravimetric Methods of Analysis Gravimetric methods of analysis are based on: weighing some form of the analyte after it precipitates weighing the analyte after evolution of a gas weighing the gas evolved from a sample (evolved gas analysis) s aq aq AgCl Cl Ag → + - + (g) 2 (g) (s) Δ (s) 4 2 CO CO CaO O CaC + + → For good results, precipitating reagents should be selective , reacting with only a small number of analytes. For best results, precipitating reagents should be specific , reacting with only a single analyte.
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Gravimetric Analyses with Organic Agents
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Procedure Requirements for Precipitates used in Gravimetry: - Readily filterable and washed free of contaminants - Low solubility to ensure no significant loss during filtration and washing - Chemically inert to the atmosphere - Of known composition after it is dried or ignited CaC 2 O 4 CaCO 3 CaO PRECIPITATE FILTER DRY or IGNITE WEIGH PREPARE THE SOLUTION DIGEST WASH CALCULATE
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Obtaining the Right Particle Size for Filtration When the supersaturation is large, precipitate tends to be colloidal. When it is small, precipitate tends to be crystalline. S S Q (SS) ation Supersatur Relative - = Analyte concentration at any instant Equilibrium solubility Given by K sp S S S
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Precipitate under the right conditions. Obtaining the Right Particle Size Keep relative supersaturation low! Increase S (precipitate at low pH (anion is protonated and then precipitate is more soluble), precipitate from hot solution).
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