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Thread: HELP!! PLEASE!! hydrogen peroxide in acidic conditions?

  1. #1 HELP!! PLEASE!! hydrogen peroxide in acidic conditions? 
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    please help i am doing an investigation into the rate of decomposition of hydrogen peroxide and as an extention i looked into the rate in acididic and alkaline conditions, thinking that le chatiers principle would make it shift to the right under acidic conditions and thefore the rate of reaction would be faster, however i cannot find anything written supporting my theory, is there any one out there that can help apart from my tutors who r refusing!! thankyou sooo much!!


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  3. #2 Erm 
    Forum Professor leohopkins's Avatar
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    H2O2 Is Alkeline, is it not ?

    Therefore adding an acid would slow down any reaction by reducing its Ph value towards 7.


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  4. #3  
    Forum Sophomore Matt Lacey's Avatar
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    Hydrogen peroxide is weakly acidic, though I'm not sure what effect this has on the reaction 2H<sub>2</sub>O<sub>2</sub> --> 2H<sub>2</sub>O + O<sub>2</sub> since acid/base isn't involved in this equilibrium.

    I believe hydrogen peroxide is sensitive to alkaline pH but I'm not sure how much, or what the mechanism is... perhaps something like

    H<sub>2</sub>O<sub>2</sub> + OH<sup>-</sup> --> HOO<sup>-</sup> + H<sub>2</sub>O

    HOO<sup>-</sup> + OH<sup>-</sup> --> H<sub>2</sub>O + O<sub>2</sub>

    I dunno, I have no evidence for that random guess.

    Still, I don't think Le Chatelier's principle will explain anything for you because this isn't an equilibrium, it's a spontaneous exothermic decomposition. Le Chatelier's principle tells you about position of equilibrium (ie forward and backward reaction rates are equal) - this is about rate constant for the forward reaction only - there is no equilibrium since one of your products, oxygen, is escaping.

    There is a catalyst for decomposition under acidic conditions which is something like KI, for example.
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  5. #4  
    Forum Professor leohopkins's Avatar
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    Quote Originally Posted by Matt Lacey
    Hydrogen peroxide is weakly acidic
    REALLY? I thought H2O2 was a bleaching agent and therefore alkaline ?
    The hand of time rested on the half-hour mark, and all along that old front line of the English there came a whistling and a crying. The men of the first wave climbed up the parapets, in tumult, darkness, and the presence of death, and having done with all pleasant things, advanced across No Man's Land to begin the Battle of the Somme. - Poet John Masefield.

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  6. #5  
    Forum Ph.D. Nevyn's Avatar
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    it is a bleaching agent, they use it in blonde hair dyes
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  7. #6  
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    Being a bleach says nothing about it's acidity just that it is an oxidising or reducing agent.
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  8. #7  
    Forum Ph.D. Nevyn's Avatar
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    it's an alkaline, it has a Ph of 11.65
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  9. #8  
    Forum Professor leohopkins's Avatar
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    'Nuff Said.
    The hand of time rested on the half-hour mark, and all along that old front line of the English there came a whistling and a crying. The men of the first wave climbed up the parapets, in tumult, darkness, and the presence of death, and having done with all pleasant things, advanced across No Man's Land to begin the Battle of the Somme. - Poet John Masefield.

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  10. #9  
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    Quote Originally Posted by Nevyn
    it's an alkaline, it has a Ph of 11.65
    11.65 is the pKa value which is the log of the acid dissociation constant not the pH. As pH is a measure of the dissociation of Hydroxide ions, its value is entierly dependant on the concentration of the solution. If you look at the pH values for hydrogen peroxide at different concs it is indeed weakly acidic as it will readily dissociate to donate H+ ions.

    To give a rough idea of Hydrogen Peroxides acidity a 10% solution will have a pH of around 5.5 and a 60% solution of 4.5.
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  11. #10  
    Forum Ph.D. Nevyn's Avatar
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    oops, sorry Leo, looks like i made a mistake :?
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  12. #11  
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    Peroxide reacts with most acids to form a peracid, your solution will still be acidic
    Man casts a long shadow only at morning and sunset. He stands in his own shadow at the height of his noon.
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  13. #12 Re: HELP!! PLEASE!! hydrogen peroxide in acidic conditions? 
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    Hello to all! I'm new on this Forum
    Quote Originally Posted by xjessiemagoox
    please help i am doing an investigation into the rate of decomposition of hydrogen peroxide and as an extention i looked into the rate in acididic and alkaline conditions, thinking that le chatiers principle would make it shift to the right under acidic conditions and thefore the rate of reaction would be faster, however i cannot find anything written supporting my theory, is there any one out there that can help apart from my tutors who r refusing!! thankyou sooo much!!
    When you say "rate of decomposition" you mean the speed of the reaction:
    H2O2 --> H2O + (1/2)O2
    or you mean the reaction's speed with a reducing substance? It's not the same thing.
    Furthermore, what you talk about Le Chatelier Principle, refers to the reaction's equilibrium constant, that is, the amount of products relative to the amount of reagents, and not to the reaction's rate.
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  14. #13 Re: Erm 
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    Quote Originally Posted by leohopkins
    H2O2 Is Alkeline, is it not ?

    Therefore adding an acid would slow down any reaction by reducing its Ph value towards 7.
    H<sub>2</sub>O<sub>2</sub> is a weak acid, but it can be basic under very acidic conditions, forming a [H<sub>3</sub>O<sub>2</sub>]<sup>+</sup> ion.
    "There is a kind of lazy pleasure in useless and out-of-the-way erudition." -Jorge Luis Borges
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  15. #14 Re: Erm 
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    Quote Originally Posted by Chemboy
    Quote Originally Posted by leohopkins
    H2O2 Is Alkeline, is it not ?

    Therefore adding an acid would slow down any reaction by reducing its Ph value towards 7.
    H<sub>2</sub>O<sub>2</sub> is a weak acid, but it can be basic under very acidic conditions, forming a [H<sub>3</sub>O<sub>2</sub>]<sup>+</sup> ion.
    Yes, H<sub>2</sub>O<sub>2</sub> is a bit more acid than H<sub>2</sub>O, even if I wouldn't say it's a weak acid: its Ka is 10<sup>-11.65</sup>.

    It's true that it can be basic under very acidic conditions forming [H<sub>3</sub>O<sub>2</sub>]<sup>+</sup>. It is more difficult than with water, however,

    so H<sub>2</sub>O<sub>2</sub> is less basic than water (and so [H<sub>3</sub>O<sub>2</sub>]<sup>+</sup> is more acid than H<sub>3</sub>O<sup>+</sup>), but I don't know how much.

    I would like to know it.
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