Mirco-Scale Acid-Catalysed Iodination of Acetone.

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Mirco-Scale Acid-Catalysed Iodination of Acetone. Abstract: The purpose of this experiment was to titrate different concentrations of HCl and ClCHCOOH against Na2S2O3. The volumes found were plotted against time and values for Kobs , KH+ and KHA were found from these graphs. The Kobs values found for each experiment were (i)Kobs = 2.48x10-6, (ii)Kobs = 6.2x10-7, (iii)Kobs = 5.3x10-7, (iv)Kobs = 4.6x10-7. The values found for KH+ for the reaction using HCl as the acid were found to be (i)KH+ = 4.96x10-5, (ii)KH+ = 1.24x10-5, (iv)KH+ = 1.84x10-5. The KHA value for the reaction using ClCHCOOH as the acid was found to be (iii) KHA = 2.985. Introduction: The aim of this experiment is to perform a titration of an acid, HCl/ClCHOOH against Na2S2O3. Form plotting the results we then want to find Kobs for each reaction and KH+/KHA for the reactions. Kobs is the slope on the graph plotting Vol of NaaS2O3 against time. Specific hydrogen ion catalysis Kobs = KH+[H+] This is used when a strong acid is being used in the reaction as it acid fully dissociated and there is no A- value. This is the equation used for reactions (i), (ii) and (iv) as they used HCl as the acid. General acid catalysis Kobs = KH+[H+] + KHA[HA]. This is used when a weak acid is being used in the reaction as it acid does not fully dissociated and there is an A- value. This is the equation used for reaction (ii) as it used ClCHCOOH as the acid. Results, Observations and Discussion: (ii) 0.25M HCl | (iii) 0.5M Cl2CHCOOH | (iv) 0.125M HCl | Time(mins) | Vol (Na2S2O3) | Time(mins) | Vol(Na2S2O3) | Time(min) | Vol (Na2S2O3) | 0 | 0.46 | 0 | 0.4 | 0 | 0.33 | 6 | 0.44 | 8 | 0.4 | 6 | 0.28 | 12 | 0.4 | 16 | 0.36 | 12 | 0.24 | 18 | 0.36 | 24 | 0.29 | 18 | 0.22 | 24 | 0.32 | 32 | 0.26 | 24 | 0.2 | 30 | 0.28 | 40 | 0.2 | 30 | 0.19 | Calculations: Finding Kobs - (ii) -dI2dt=0.005

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