221-chapter-7

221-chapter-7 - Titrations Introduction 1.) Buret Evolution...

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Titrations Introduction 1.) Buret Evolution Primary tool for titration Descroizilles (1806) Pour out liquid Gay-Lussac (1824) Blow out liquid Henry (1846) Copper stopcock Mohr (1855) Compression clip Used for 100 years Mohr (1855) Glass stopcock
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Titrations Introduction 2.) Volumetric analysis Procedures in which we measure the volume of reagent needed to react with an analyte 3.) Titration Increments of reagent solution (titrant) are added to analyte until reaction is complete. - Usually using a buret Calculate quantity of analyte from the amount of titrant added. Requires large equilibrium constant Requires rapid reaction - Titrant is rapidly consumed by analyte Controlled Chemical Reaction
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Titrations Introduction 4.) Equivalence point Quantity of added titrant is the exact amount necessary for stoichiometric reaction with the analyte - Ideal theoretical result Analyte Oxalic acid (colorless) Titrant (purple) (colorless) (colorless)
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Titrations Introduction 5.) End point What we actually measure - Marked by a sudden change in the physical property of the solution - Change in color, pH, voltage, current, absorbance of light, presence/absence ppt. CuCl Titration with NaOH Before any addition of NaOH After the addition of 8 drops of NaOH End Point
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Titrations Introduction 5.) End point Occurs from the addition of a slight excess of titrant - Endpoint does not equal equivalence point Analyte Oxalic acid (colorless) Titrant (purple) (colorless) (colorless)
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Titrations Introduction 5.) End point Titration Error - Difference between endpoint and equivalence point - Corrected by a blank titration i. repeat procedure without analyte ii. Determine amount of titrant needed to observe change iii. subtract blank volume from titration Primary Standard - Accuracy of titration requires knowing precisely the quantity of titrant added. - 99.9% pure or better accurately measure concentration Analyte Oxalic acid (colorless) Titrant (purple)
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Introduction 6.) Standardization Required when a non-primary titrant is used - Prepare titrant with approximately the desired concentration - Use it to titrate a primary standard - Determine the concentration of the titrant - Reverse of the normal titration process!!! titrant known
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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-7 - Titrations Introduction 1.) Buret Evolution...

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