Kinetics of Crystal Violet Bleaching

Kinetics of Crystal Violet Bleaching - Kinetics of Crystal...

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Kinetics of Crystal Violet Bleaching 1, 2 Authors: V. C. Dew and J. M. McCormick* Last Update: December 29, 2006 Introduction Chemists are always interested in whether a chemical reaction can occur and exactly how it occurs. The first question is answered though thermodynamics, as you saw in the previous laboratory exercise , while the second is the domain of kinetics. In a kinetics experiment, a chemist attempts to understand the step-by-step transformation of reactants to products. Taken together these elementary steps gives us the mechanism by which the reaction proceeds. Note that a reaction's kinetics are very much tied to the pathway the reactants take to the products (i. e., the mechanism), which is very different from the reaction's thermodynamic properties (i. e., H, S and G) that do not depend on the path. While the thermodynamics and kinetics of a reaction may at times seem complimentary, and at other times seem contradictory, it is always important to have a detailed understanding of both. In this experiment you will determine the rate law for a chemical reaction. The rate law is a mathematical expression that relates the amount of time it takes a reaction to happen to the concentrations of the starting materials. The disappearance of reactant over time depends on the rate constant , and the concentration of each reactant raised to some power. This power, known as the order of reaction with respect that reactant. The sum of the individual orders is the overall order of the reaction . The order of reaction with respect to each reactant, as well as the rate law itself, cannot be determined from the balanced chemical equation; it must be found experimentally ( More Info ). The rate law is the basic equation of kinetics and it will be the standard against which we judge possible mechanisms. Scheme 1. Reaction of crystal violet with OH - .
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In this experiment you will determine the rate law for the reaction of a dye, crystal violet (CV) with OH - in aqueous solution according to the balanced net ionic equation given in Scheme 1. We will define the rate of reaction as the disappearance of the colored CV over time, which can be expressed in differential form as d [ CV ]/ dt . So, the rate law for this reaction can be written as shown in Eqn. 1 in terms of the concentration of CV and OH - and the rate constant for the reaction, k . In writing this equation we assume that both CV and OH - are involved in the reaction (that is x and y are both not zero and are likely integers), but only the experiment will tell us whether these assumptions are valid. (1)
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This lab report was uploaded on 04/17/2008 for the course CHEM 121 taught by Professor Baughman during the Spring '08 term at Truman State.

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Kinetics of Crystal Violet Bleaching - Kinetics of Crystal...

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