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General Chemistry Lab

General Chemistry Lab. Rates of Chemical Reactions, I: The Iodination of Acetone Experiment 20, p.155. ( aq ). I 2 ( aq ). H 3 C. CH 2 I. + H + ( aq ) + I - ( aq ). +. [I 2 ]. Rate = —. acetone.  t. O. O. CH 3. C. C. H 3 C. Rate = k [acetone] m [I 2 ] n [H + ] p.

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General Chemistry Lab

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  1. General Chemistry Lab Rates of Chemical Reactions, I: The Iodination of Acetone Experiment 20, p.155

  2. (aq) I2(aq) H3C CH2I + H+(aq) + I-(aq) + [I2] Rate = — acetone t O O CH3 C C H3C Rate = k [acetone]m [I2]n [H+]p We want you to determine the value of m, n, and p. Abbreviate [acetone] as [A]

  3. (aq) I2(aq) H3C CH2I + H+(aq) + I-(aq) + acetone O O CH3 C C H3C colored colorless We can follow the course of the reaction by observing color changes. Rate = k [A]m [I2]n [H+]p The reaction is zero order with respect to I2 (n = 0). So the rate does not depend on [I2] at all, as long as [I2] is not = 0. In the lab, you will make I2 the limiting reagent, present in a large excess of acetone and H+, so the [ ] of these effectively do not change.

  4. (aq) I2(aq) H3C CH2I + H+(aq) + I-(aq) + acetone O O CH3 C C H3C The rate of the reaction is constant during its course under these conditions, so we can vary the rate by changing the initial [A] and [H+].

  5. (aq) I2(aq) H3C CH2I + H+(aq) + I-(aq) + acetone ( ) Rate 2 k 2[A]m Rate 1 k [A]m m 2[A] = 2m O O = = CH3 [A] C C H3C If we double the [A] while holding the [ ] of the other two constant Rate 2 = k 2[A]m [I2]0 [H+]p Rate 1 = k [A]m [I2]0 [H+]p What happened to the other terms in these equations?

  6. So by timing these two reactions, we can discover the order of the reaction with respect to [A] (that is, the value of m).

  7. (aq) I2(aq) H3C CH2I + H+(aq) + I-(aq) + acetone O O CH3 ( ) Rate 2 k 2[H+]p Rate 1 k [H+]p p 2[H+] = 2p C C = = [H+] H3C Next we double the initial [H+] while holding the [ ] of the other two constant Rate 2 = k [A]m [I2]0 2[H+]p Rate 1 = k [A]m [I2]0 [H+]p

  8. So by timing these two reactions, we can discover the order of the reaction with respect to [H+] (that is, the value of p).

  9. Before you arrive at chemistry lab, read and study the introduction to Lab Exercise 20 (p.155). Then read and re-read the “Experimental Procedure” on pp.157-161 until you completely understand what you will do. Next week you will need to do this for Lab Exercise 21: Rates of Chemical Reactions, II. A Clock Reaction (p.165). This ppt file is available on my web sitehttp://www.evangel.edu/Personal/badgers/Web/

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