221-chapter-11

221-chapter-11 - Acid-Base Titrations Introduction...

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Acid-Base Titrations Introduction
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Acid-Base Titrations The p K of His-240 in the G6PD apoenzyme is found to be 6.4, which corresponds to an unidentified p K a value of 6.3 that was previously derived from the dependence of k on pH. These results suggest that the p K a of His-240 is unperturbed by Asp. Biochemistry, Vol. 41, No. 22, 2002 6945 Introduction 2.) Example: impact of the Asp on the p K a of His in the His-Asp catalytic dyad. - Glucose 6-phosphate dehydrogenase (G6PD) catalyzes the oxidation of glucose 6-phosphate using NAD + or NADP + - His-240 is the general base that extracts a proton from the C1-OH of G6P
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Acid-Base Titrations Introduction 3.) Overview Titrations are Important tools in providing quantitative and qualitative data for a sample. To best understand titrations and the information they provide, it is necessary to understand what gives rise to the shape of a typical titration curve. To do this, acid-base equilibria are used to predict titration curve shapes. J. Phys. Org. Chem. 2006; 19: 129–135 conformational change of the PAA from rod-like conformation to a random coil form, proton release from PAA decreases with increase in the degree of dissociation for the highest polymer concentration
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Acid-Base Titrations Titration of Strong Base with Strong Acid 1.) Graph of How pH changes as Titrant is Added Assume strong acid and base completely dissociate Any amount of H + added will consume a stoichiometric amount of OH - Reaction Assumed to go to completion Three regions of the titration curve - Before the equivalence point excess OH- in the solution - At the equivalence point , H + with all OH - to make H 2 O - After the equivalence point , pH is determined by excess H + in the solution. 14 w 10 K 1 K = =
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Acid-Base Titrations Titration of Strong Base with Strong Acid 1.) Graph of How pH changes as Titrant is Added Remember, equivalence point is the ideal goal Actually measure End Point - Marked by a sudden physical change: color, potential Different Regions require different kinds of calculations - Illustrated examples The “true” titration reaction is: Titrant Analyte
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Acid-Base Titrations Titration of Strong Base with Strong Acid 2.) Volume Needed to Reach the Equivalence Point Titration curve for 50.00 mL of 0.02000 M KOH with 0.1000 M HBr A t equivalence point , amount of H + added will equal initial amount of OH - ( 29 ( 29 ( 29 mL 00 . 10 V ) M 02000 . 0 ( mL 00 . 50 M 1000 . 0 ) mL ( V e e = = mmol of HBr at equivalence point mmol of OH - being titrated When 10.00 mL of HBr has been added, the titration is complete. Prior to this point, there is excess OH- present.
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Acid-Base Titrations Titration of Strong Base with Strong Acid 3.) Before the Equivalence Point Titration curve for 50.00 mL of 0.02000 M KOH with 0.1000 M HBr - Equivalence point (V e ) when 10.00 mL of HBr has been added - When 3.00 mL of HBr has been added, reaction is 3/10 complete ( 29 M 0132 . 0
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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-11 - Acid-Base Titrations Introduction...

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