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Clock Reaction Inconsistency ?

  1. Aug 9, 2010 #1
    Hello,
    I have recently been conducting a Clock reaction but has come up with a few inconsistency's. The aim is to measure the effect of verying amounts of catalyst on a clock reaction rate. The rate in turn is measured by a colorimeter.
    I started out by doing an initial experiment by adding .1ml of catalyst to 20ml of reactants and increased the amount of catalyst to .6ml each trial was done 3 times. The initial problem here was .2ml and .3ml were practically identical (took 40 seconds ruffly) but so were .05ml and 6ml (took 10 seconds)

    I though it was perhaps varying the overall volume of the reactants as well as the concentration, so i re-designed the experiment adding water to eliminate any volume differences. I did this as accurately as humanly possible for me.
    2ml of each reactant was measured out with a pipete with a max volume of 2ml.
    Then identical droppers were used to add water and catalyst. This time it was looking good till I got to 4/10 drops as catalyst in which the first one went as planned. The second one had only half the darkness in blue and the third one didn't react at all.

    I than went on to test ten out of ten drops as a catalyst. In case the Catalyst (HCL) was breaking down the starch in the reaction which would cause a failure in color change. This is where things get weird. If i combine the two and shook them when combining i get the expected color. If i don't shake it i get about 1/100th of what the color should be. Shaking it after the reaction occurred does not change anything about the color The reactionrate was the same for shaken or not. This then suggests that by shaking the reaction i shift the equilibrium position. Is this possible or am i overlooking a simple variable?

    Any input would be greatly appreciated. I can post my raw data as well as images of color if it's needed.

    Moss,
     
  2. jcsd
  3. Aug 9, 2010 #2

    Borek

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    Staff: Mentor

    You better post information about the reaction you are researching. While I guess I know what reaction it is, guessing is not the best starting point.

    Was the starch fresh?

    I always thought you don't need a colorimeter, you just wait till solution turns blue.

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  4. Aug 9, 2010 #3
    Note that the color in the test tube have reverted back to clear. All the color in the petrie dishes have stayed the same
     

    Attached Files:

  5. Aug 9, 2010 #4
    Here is the graph. Feel free to ask question... I NEED HELP :'(
     
  6. Aug 9, 2010 #5
    Sorry upload failed before.
     

    Attached Files:

  7. Aug 10, 2010 #6

    chemisttree

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    Gold Member

    You should investigate the role diffusion plays in the rate of your reaction. How is diffusion affected by your catalysts? Is diffusion the factor most responsible for the rate of your reaction? If so, how would adding a catalyst affect the global rate of reaction?
     
  8. Aug 10, 2010 #7

    Borek

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    I already asked the question and asked you to post information about the reaction... We are still forced to guess what reagents you have used, what concentrations and so on.

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    methods
     
    Last edited: Aug 10, 2010
  9. Aug 10, 2010 #8
    We where not told exactly what each substance was they where simply labeled solution A and solution B the catalyst used was HCL of .1 mol/L. I will try and get the exact chemicals tomorrow.
     
  10. Aug 10, 2010 #9

    Borek

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    Staff: Mentor

    Ah OK, that's the way it is done.

    Think about what chemisttree posted. Have you just added the catalyst? Have you shaken the solution, so that it was properly mixed and homogeneous?

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