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Chemical Method for Studying the Variation of [A] with Time

p.01. Chemical Method for Studying the Variation of [A] with Time. C. Y. Yeung (CHW, 2009). sampling,. quenching, and. titration. p.02. Chemical Method = …. Monitoring the change of conc. along with time by:. p.03. Example 1:. O. O. +. +. R’OH. OH -. O -. R. C. OR’. R. C.

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Chemical Method for Studying the Variation of [A] with Time

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  1. p.01 Chemical Method for Studying the Variation of [A] with Time C. Y. Yeung (CHW, 2009)

  2. sampling, quenching, and titration p.02 Chemical Method = … Monitoring the change of conc. along with time by:

  3. p.03 Example 1: O O + + R’OH OH- O- R C OR’ R C (aq) (aq) (aq) (aq) Step1: Known amounts of ester and NaOH in beakers are placed in a thermostatic bath at known temperature. Step2: Start the reaction by mixing the reactants rapidly. The time is noted. Step3: At regular time intervals, a fixed volume of the mixture is pipetted into about 5 volumes of ice-water to quench the reaction.

  4. p.04 Example 1 (continued): O O + + R’OH OH- O- R C OR’ R C (aq) (aq) (aq) (aq) Step4: Remaining [OH-] in the reaction mixture is determined by titration against standard HCl using phenolphthalein. Step5: Repeat steps 3 and 4 to obtain variation of [OH-] against t.

  5. p.05 Example 2: O O H+ catalyst + + HI I2 CH2I R C CH3 R C Step1: Known amounts of ketone, I2 and HCl in beakers are placed in a thermostatic bath at known temperature. Step2: Start the reaction by mixing the reactants rapidly. The time is noted. Step3: At regular time intervals, a fixed volume of the mixture is pipetted into NaHCO3(aq) to quench the reaction by removing the H+ catalyst.

  6. p.06 Example 2 (continued): O O H+ catalyst + + HI I2 CH2I R C CH3 R C Step4: Remaining [I2] in the reaction mixture is determined by titration against standard Na2S2O3(aq) using starch indicator. Step5: Repeat steps 3 and 4 to obtain variation of [I2] against t.

  7. p.07 Example 3: MnO2(s) O2(g) 2H2O(l) 2H2O2(aq) + Step1: Known amounts of H2O2 is mixed with a small amount of MnO2(s) catalyst in a beaker placed in a thermostatic bath at known temperature. Step2: At regular time intervals, a fixed volume of the mixture is pipetted into excess dilute H2SO4(aq) to quench the reaction by removing the MnO2(s) catalyst.

  8. p.08 Example 3 (continued): MnO2(s) O2(g) 2H2O(l) 2H2O2(aq) + Step4: Remaining [H2O2] in the reaction mixture is determined by titration against standard KMnO4(aq). 5H2O2 + 2MnO4- + 6H+ 2Mn2+ + 8H2O + 5O2 Step5: Repeat steps 3 and 4 to obtain variation of [H2O2] against t.

  9. O O H+ + + C2H5OH H2O OH CH3 C OC2H5 CH3 C QUESTION: p.09

  10. p.10 Next …. Physical Method for Studying the Variation of [A] with Time

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