07MANCVhydroxylation - Crystal Violet Hydroxylation Revised...

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Crystal Violet Hydroxylation Revised 11/03/10 1 CRYSTAL VIOLET HYDROXYLATION REACTION Adapted from "Chemistry with Computers" Vernier Software, Portland OR, 1997 OBJECTIVES For you, the student, to write…. SAFETY Wear safety goggles and lab aprons at all times in lab. Sodium hydroxide is caustic and can cause burns. Wash any affected areas immediately with cold water. Crystal violet leaves stains when spilled. Protect skin and clothing from contact and wash hands and glassware thoroughly when experiment is finished. INTRODUCTION In this experiment, you will investigate the kinetics of the reaction between crystal violet and sodium hydroxide. The equation for the reaction is shown below: C OH N(CH 3 ) 2 (H 3 C) 2 N N(CH 3 ) 2 C N(CH 3 ) 2 (H 3 C) 2 N N(CH 3 ) 2 + NaOH Cl Na + Cl C N(CH 3 ) 2 (H 3 C) 2 N N(CH 3 ) 2 + Cl C N(CH 3 ) 2 N(CH 3 ) 2 (H 3 C) 2 N Cl C (H 3 C) 2 N N(CH 3 ) 2 N(CH 3 ) 2 Cl + + Resonance Structures of Crystal Violet
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Crystal Violet Hydroxylation Revised 11/03/10 2 A simplified (and less intimidating!) version of the equation is: (1) CV + + OH CVOH crystal violet hydroxide ion Kinetics is the study of the speed or rate of a chemical reaction. The differential rate law for the hydroxylation of crystal violet is: (2) rate = - [CV + ] = k [CV + ] m [OH ] n t where k is the rate constant for the reaction, m is the order with respect to crystal violet (CV + ), and n is the order with respect to hydroxide ion. To determine the orders of reaction ( m and n ), the reaction will need to be done twice. Even though the balanced chemical reaction has a 1:1 mole ratio between CV + and - OH, the actual ratios of reactants used in lab will be much different. The concentration of - OH will be approximately 1000 times that of concentration of CV + in trial 1; and 500 times in trial 2. In both trials, the hydroxide ion is in huge excess and can be assumed constant - neither will change appreciably during the reaction. Therefore, the hydroxide's concentration term and reaction order is grouped with the rate constant, k, to create the pseudo rate constants, k 1 and k 2 . This allows for the simplification of the rate law: (3) rate 1 = - [CV + ] = k 1 [CV + ] m where k 1 = k[OH ] 1 n ; [OH ] 1 is 0.020 M. t (4) rate 2 = - [CV + ] = k 2 [CV + ] m where k 2 = k[OH ] 2 n ; [OH ] 2 is 0.010 M. t To find the reaction order of CV + , m, and the pseudo rate constants, k 1 and k 2 , differential rate laws expressed in equations 3 & 4 must be integrated. (You should review integrated rate laws in your lecture text before continuing.) Integrated rate laws, when arranged in line equation form, result in a mathematical function of concentration for the y axis and time on the x axis. The mathematical function of concentration and the slope reveal the values of m, k
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This note was uploaded on 11/21/2010 for the course CHEMISTRY Chem 1LE taught by Professor Dr.kimberlyedwards during the Spring '10 term at UC Irvine.

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07MANCVhydroxylation - Crystal Violet Hydroxylation Revised...

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