2007_prelab - Department of Chemical Engineering University...

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Department of Chemical Engineering University of Cambridge – Weblab Exercise (due April 6, 2007 at 1 pm) Note: Parts A – D should be completed before the Weblab on Monday, March 19, 2007, but don’t have to be turned in until April 6, 2007. Introduction This exercise concerns the reaction of phenolphthalein (PHEN) in an aqueous solution of sodium hydroxide: PHEN + 2OH - PHEN 2- + 2H 2 O (1) PHEN 2- + OH - PHENOH 3- (2) (pink) (colourless) Reaction (1) can be assumed to occur rapidly, so the rate determining step is reaction (2). The rate laws for reaction (2) are: r 1 = k 1 [PHEN 2- ][OH - ] ( 3 ) r 2 = k 2 [PHENOH 3- ] ( 4 ) The purpose of this exercise is to determine the reaction constants for this reaction, and to predict the operating conditions required to achieve a given conversion of PHEN 2- to PHENOH 3- in a non-ideal reactor. You will test your predictions by running experiments on the reactor in question. PART A http://weblabs.cheng.cam.ac.uk/reactors_batchdata.html contains experimental data from reactions (1) and (2) carried out in a batch reactor. To track the progress of the reaction, a spectrophotometer has been used to measure the intensity of light (550 nm) transmitted through the reaction solution. This intensity, I , is related to the concentration, c , by the Beer-Lambert law: c = –b * ln (I/I 0 ) (5) Note: As concentration increases (more pink stuff), the intensity of light passing through the sample decreases (c up, I down). b is positive, but knowing the value is unnecessary because it will cancel out. Show that the time variation of the intensity, I, through the experiment can be expressed
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2007_prelab - Department of Chemical Engineering University...

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