The concentration of hypochlorite ion ocl in the

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The concentration of hypochlorite ion, OCl - , in the reaction solution will be more than 500 times larger than the concentration of Blue#1. The large excess of OCl - ion means that its concentration will remain essentially constant during the reaction. Thus, we may combine the constant term, OCl n - é ù ë û , with the actual rate constant, k, into an apparent rate constant which is given the symbol k’. The equation is [ ] [ ] ' m d Blue#1 Rate k Blue#1 dt = - = (5.3) where k ' = k i OCl n (5.4) Thus, if we perform an experiment where the concentration of the OCl - ion remains essentially constant (as it will be for all of our kinetic experiments), analysis of the data will provide the values of m and k’ . At this stage you should review the integrated rate laws from Zumdahl. In brief, you will determine if the reaction is zero, first, or second order by a graphical analysis of the data. If the reaction is first order with respect to [Blue#1], that is, if m = 1, then a plot of ln Blue#1 ! " # $ as a function of time will best characterize the data because ln Blue#1 ! " # $ = k ' t + ln Blue#1 ! " # $ 0 (5.5) If the reaction is second order with respect to [Blue#1], that is, if m = 2, then [ ] [ ] 0 1 1 ' k t Blue#1 Blue#1 = + (5.6)
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Chemistry 132 Lab Manual Page 57 If the reaction is zero order with respect to [Blue#1], that is, if m = 0, then [ ] [ ] 0 ' Blue#1 k t Blue#1 = - + (5.7) where [ ] 0 Blue#1 represents the concentration immediately after mixing the reagents, at zero time, before reaction. If you know the concentration of the Blue#1 stock solution, and the volumes of the solutions added, you can calculate the value of [ ] 0 Blue#1 , although as you see from Eqns. 5.5 – 5.7, [ ] 0 Blue#1 is a constant term that does not impact the value of the slope determined. Part B. Design an experiment to determine the value of n , that is, the order of the reaction of Blue#1 (Blue food dye) with respect to the concentration of OCl - . Look back at Equations 5.5 – 5.7 where you notice that the coefficient n does not appear directly, but rather is there implicitly. Review Equation 5.2. If you think (and talk with your lab partner) about these kinetic equations you should be able to design an experiment that will allow you to determine the value of n . Discuss your plans with your TA, or ask for help if you are not certain how to proceed. Part C . Determine the rate constant for the reaction of Green food dye with OCl . Of course, the first step is to record the absorption spectrum of the Green food dye and compare this to the Blue food dye (Blue#1) absorption spectrum. Part D. Determine the rate constant for the reaction of Yellow food dye with sodium hypochlorite, NaOCl. It may help if you review the experiments used for Parts A-C, before designing experiments with Yellow food dye. Experimental Details . CAUTION: Sodium hypochlorite is a bleaching agent and may be caustic. In case of contact with skin, flush the area with large amounts of water for several minutes.
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