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I'm designing an experiment to test the effect of surface area of a catalyst on the activation energy of hydrogen peroxide decomposition. However, I don't think I can use a powdered catalyst because determining its surface area would be too complex (specific surface area is beyond the scope of my course). So, I proposed using a potato as a catalyst because I can get a chunk of it and split it into smaller and smaller pieces every time I want to increase surface area but keep concentration constant. However, my chemistry teacher isn't a fan of the potato because it deals with biology as well. So I'm wondering if there is a heterogeneous catalyst for hydrogen peroxide that I can get in chunks and reasonably split it into smaller pieces? Preferably, it should be at least somewhat common to find in laboratories.

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  • $\begingroup$ Maybe titanium oxide (skittles, sun screen, road paint), see doi.org/10.1021/jp300255h $\endgroup$
    – Karsten
    Oct 19, 2022 at 3:24
  • $\begingroup$ Potato is bad in that the catalyst is the juice, not the surface. Titanium oxide is powdered. Come to think of it, I can hardly imagine finding anything which is not powdered and still active enough to be measured. $\endgroup$ Oct 19, 2022 at 7:41
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    $\begingroup$ Try manganese metal pieces. It works great. The bottle of it that I had was in the form of thin pieces with lumpy surfaces on one side and flat smooth surfaces on the other side. If I was doing it, I would melt some wax and place the manganese pieces lumpy side down on the wax. Then the smooth surfaces would be the relevant ones. $\endgroup$
    – Ed V
    Oct 19, 2022 at 13:37
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    $\begingroup$ If you search on ebay for “manganese metal”, you can see lots of the flake (electrolytic) manganese for sale. Pretty cheap, actually. Best of success with your project! $\endgroup$
    – Ed V
    Oct 19, 2022 at 13:59

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I think your question needs refinement.

Activation Energy is not affected by the surface area of the catalyst. The catalyst is providing a different mechanism to reach the final product than without it. It does this when particles of the reactants interact with the particles on the surface of the catalyst (since this is a heterogeneous catalyst).

The reason the reaction would go much faster if the heterogenous catalyst had more surface area is because of more particle-particle interactions able to take place between the catalyst and the reaction. This would be similar to why reacting a piece of iron in hydrochloric acid would go much slower than if the same sized iron were cut into 1000 pieces and placed into the same solution. The higher chance of particles to interact with each other, more likely they'll have the activation energy to form products.

A possible answer and improvement to your experiment:

If your goal is to determine how activation energy is affected by surface area, then performing the hydrogen peroxide reaction within a coffee cup calorimeter would be great. You could measure out the same amount of water for the calorimeter, use the same mass of reactants, and measure the temperature changed caused for each surface area tested. If activation energy is affected, the temperature change in the water of the coffee cup would be different.

Manganese metal suggested by @EdV is a good choice. A pricier option would be silver metal. It is very good at decomposing hydrogen peroxide, but at a higher price.

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    $\begingroup$ (+1) For the experiment improvement suggestions! I was going to suggest silver metal strip, since I have some and it works fine, but manganese is cheap and works well for this purpose. It is also very good for hydrogen generation from common mineral acids. Welcome to Chemistry Stack Exchange! $\endgroup$
    – Ed V
    Oct 19, 2022 at 20:54
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    $\begingroup$ Thanks both of you for these pieces of advice, suggestions, and improvements for my investigation. My only question is how I would go about manipulating the surface area of the catalyst. For the metal strips you suggested, for example, would cutting the strips create a big enough change in surface area to be noticeable? I also have to actually calculate the surface area so I can't use any weird shapes or anything. I originally wanted a solid chunk of something so that it would have some depth to it, allowing me to increase surface area easily by separating it into smaller pieces. $\endgroup$ Oct 20, 2022 at 2:54
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    $\begingroup$ I have posted two relevant photos at our temporary location: chemistry.meta.stackexchange.com/a/5143/79678. I tried the 99.9% pure (aka ‘fine’ or 3N) silver strip and a 20 g piece of silver of the same purity. It fails to do anything. I will check the hydrogen peroxide: maybe it has already decomposed. I know silver powder works, but then the surface area is unknown and there is no simple way, that I know of, to measure accurately the surface area of fine powder. I would go with the flake manganese. As for the silver strip failure, I will try roughening the surface with sandpaper. $\endgroup$
    – Ed V
    Oct 20, 2022 at 12:14
  • $\begingroup$ @EdV Thank you for testing this. I know I've done the powder as well. Silver does oxidize quite easily, so I am 'hoping' that the issue is with that and not somehow the metal in this form doesn't work. Which would at least give the original question asker something to discuss. Also thanks for the welcome! I <3 chemistry! $\endgroup$
    – Avogadro
    Oct 20, 2022 at 12:19
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    $\begingroup$ Sanding the silver strip works: chemistry.meta.stackexchange.com/a/5143/79678. Of course, now the surface area is not that of the formerly flat surface, but it is proportional, at least approximately, so the OP can use different size pieces. Anyway, good to know that roughened bulk silver metal works! $\endgroup$
    – Ed V
    Oct 20, 2022 at 22:55

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