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Experiment for testing type of catalyst on reaction rate?

  1. Oct 12, 2015 #1
    < Mentor Note -- thread moved to HH from the technical forums, so no HH Template is shown >

    experiment for testing type of catalyst on reaction rate?

    I need an experiment (just the method) Where I can test the reaction rate of changing the catalyst type

    I need about 3 differnet catalysts e.g. manganese oxide

    it's the rate of decomposition of hydrogen peroxide

    Thanks
    !!!!
     
    Last edited by a moderator: Oct 13, 2015
  2. jcsd
  3. Oct 12, 2015 #2

    Ygggdrasil

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    In general, what you'd want to do is to measure the concentration of reactant or product at different timepoints during the reaction to measure the rate of reactant disapearance or product generation. So, for the decomposition of hydrogen peroxide, you could either look at the rate at which the catalyst uses up hydrogen peroxide or the rate at which the catalyst generates oxygen gas.

    For measuring hydrogen peroxide concentrations, there are some colorimetric assay you can use to measure its concentration (google h2o2 colorimetric assay). For measuring oxygen concentrations, here's a relatively simple, and fun method I found: http://www.nature.com/articles/srep03081
     
  4. Oct 12, 2015 #3
    Thank you. I am going to use the rate at which Oxygen is produced using a gas syringe. Shall I measure the product of Oxygen every 5 seconds or not because there will be three different types of catalysts I'm going to use?

    Also I need a hypothesis. Will this just be "The rate of reaction is affected by different types of catalysts" or not? I'm not entirely sure myself about this hypothesis
     
  5. Oct 12, 2015 #4

    Ygggdrasil

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    How frequently you measure depends on the overall rate of reaction. If the oxygen is generated very quickly, you'd likely need to sample very frequently. You could start with that rate (if it's feasible), look at the preliminary results and see whether you need to adjust.

    Sure, that's a reasonable hypothesis. Just be sure to devise your experiment and analysis to be able to address that hypothesis and its alternatives (for example, thinking about what sorts of statistics you'd need to accept/reject such a hypothesis).
     
  6. Oct 12, 2015 #5
    I was thinking maybe instead of measuring every 5 seconds, I could time how long it takes for 25ml of gas to be produced. Would this be a good idea? Because I could then work out the reaction rate by diving the 25 by the time taken in seconds using a stopwatch. Do you have any better idea that could get me more marks?
     
  7. Oct 12, 2015 #6

    Ygggdrasil

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    Measuring every 5 s would probably be best, especially if you want to run a negative control (no catalyst).
     
  8. Oct 12, 2015 #7
    This would give you the average rate of reaction over a (relatively long) period of time. It is unlikely to give precise results. An alternate method is to measure and compare the initial rate of reaction using different catalysts by finding the time taken to liberate a much smaller volume of oxygen, and then using this to find the average rates and compare.
     
  9. Oct 12, 2015 #8
    I'm not doing the experiment without a catalyst, though. I am just testing three catalysts to find the rate of reaction and which works the best. But
    So you mean basically measure how long it takes to get to 10ml or even less and then comparing?
     
  10. Oct 12, 2015 #9
    Yes, something along those lines. The volume selected should take around 5 seconds or less to be produced.
     
  11. Oct 12, 2015 #10

    Ygggdrasil

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    You should always try to do some form of negative control. For example, what if you didn't clean your glassware thoroughly and some catalyst from previous experiments contaminated one of your reagents?
     
  12. Oct 12, 2015 #11
    What do you mean by Negative Control? Also, what do you mean by a preliminary experiment. One before hand? But what's the purpose for that. And what catalysts would you test for it?
     
  13. Oct 12, 2015 #12
    It's a control experiment in which a result is not expected.
    It's usually an experiment done in the starting with relatively low accuracy to get a rough idea of the kind of values you are expecting. For example, it is common practice in titration experiments to perform a "rough titre" first, where the acid in the burette is not run off so carefully. The idea behind it is to obtain a rough value around which neutralization occurs (indicator changes color), such as between 25-30 cm^3. This enables you to run off the acid quickly and bring it close to 20 cm^3 in the next experiment and then slow down and carefully determine the end point (allowing you to zoom in on the value faster).
     
  14. Oct 12, 2015 #13

    Ygggdrasil

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    A reaction where your experimental variable (catalyst) is not present. For example, if you experiment involved mixing 5 mL of a hydrogen peroxide solution with 1mL of your catalyst dissolved a diluent, in your negative control, you would add 1 mL of the diluent (without any catalyst in it) to the 5 mL of hydrogen peroxide solution. In the case of solid-phase catalysts like Mn, you could probably just omit that step for your negative control.
     
  15. Oct 12, 2015 #14
    Hmm. Well in the case of my objective I don't think it is necessary for me to do one as instructed. Thanks, though; I'll remember for the future.

    I am using these equipment, but I would like some things queried.

    Rubber bung
    Delivery Tube
    Gas Syringe (do I need to state it's volume?)
    Conical Flash (to contain the catalyst)
    Manganese Oxide
    Copper Oxide
    Zinc Oxide
    Spatula (to measure the catalyst) (How much would be suitable to use?)
    Hydrogen Peroxide
    Measuring Cylinder (to measure the hydrogen peroxide)
    StopWatch
    Goggles
    Clamp Stand
     
    Last edited: Oct 12, 2015
  16. Oct 12, 2015 #15
    Another query too: Should I say, for the equipment, "A selection of catalysts" or just three catalysts that I want to use(Manganese Oxide, zinc oxide, copper oxide) - wouldn't this make it more reproducible?
     
  17. Oct 12, 2015 #16

    Ygggdrasil

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    In the materials, section you should clearly state which catalysts you're testing.

    When thinking about the amount of catalyst to add, it's worth thinking about how you will compare the efficiencies of the catalysts in order to test your hypothesis. Will the rate of reaction depend on the amount of catalyst added? Will it depend on the weight of catalyst added, the number of moles of catalyst, or some other factor?
     
  18. Oct 12, 2015 #17
    So I should list my three catalysts that I want to use?
    Is it manganese oxide or manganese dioxide

    I keep reading that they are the same but clearly not. Which should I use in an investigation? Manganese oxide?
     
  19. Oct 12, 2015 #18
    Actually it's manganese (IV) oxide. Manganese is a transition element (it has an incomplete d sub-shell) and has variable oxidation states. It is standard practice to give the oxidation state of the atom with variable ox. states in brackets while naming a particular compound (unless all the atoms in the compound have fixed ox. states).
     
  20. Oct 12, 2015 #19
    Thank you
    ALso are they the correct equipment? I'm not sure if I should say the volume of the containers e.g. the measuring cylinder or conical flask?
     
  21. Oct 12, 2015 #20
    Also, what would the independent variables and dependent variables be in this investigation?
     
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