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Thread: chemistry titration question

  1. #1
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    chemistry titration question

    A solution of (NH4)2SO4·FeSO4·6H2O (hydrated ammonium iron(II) sulfate), used as a primary
    standard, was prepared by dissolving 8.82 g of the crystals in dilute sulfuric acid and making the
    solution up to exactly 250 cm3 with deionised water. This standard solution was titrated in
    25.0 cm3 portions, to which some more dilute sulfuric acid had been added, with a solution of
    potassium manganate(VII) (KMnO4). On average, 20.45 cm3 of the potassium manganate(VII)
    solution were required for complete oxidation of the Fe2+ ions.
    The equation for the titration reaction is:


    (MnO4^–1) + (5Fe^2+) + (8H^+1)→ (Mn^2+) + (5Fe^3+) + 4H2O




    (b) Explain why it was necessary
    (i) to use dilute sulfuric acid when preparing the standard solution from hydrated
    ammonium iron(II) sulfate,

    why did the sulfuric acid had to be dilute does anyone know?
    Last edited by markosheehan; Jul 29th 2017 at 02:55 AM.
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  2. #2
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    Re: chemistry titration question

    Acidic conditions are necessary, because in neutral or alkaline
    conditions Mn+7 is reduced only as far as Mn+4. Hydrochloric acid is not
    suitable as it would react with the KMnO4, and chlorine gas would be
    evolved. Nitric acid is not suitable as it is itself a very powerful oxidising
    agent - the NO3
    -
    ion is readily reduced.

    Google search produced this
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  3. #3
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    Re: chemistry titration question

    Thanks but why does it have to be dilute? And not concentrated sulfuric acid
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    Re: chemistry titration question

    It is concentrated sulfuric acid until the other compound is added to dilute it. That's what a dilution is, isn't it? Maybe I'm misunderstanding. Chemistry is not my forte. After all, this is a math help forum.

    Chemistry is not really a Math Topic.
    Last edited by SlipEternal; Jul 29th 2017 at 05:25 AM.
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  5. #5
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    Re: chemistry titration question

    There is a Chemistry Help tab at the top of the page ... can't say much about it other than it exists.
    Thanks from markosheehan
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    Re: chemistry titration question

    Sulfuric acid = hijklmnoooopqrs

    h to s, o four
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  7. #7
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    Re: chemistry titration question

    I can't understand you. It says dilute sulfuric acid is added instead of concentrated, so I am assuming it was dilute for a reason.

    It's says that chemistry questions can be posted in this section.
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  8. #8
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    Re: chemistry titration question

    Quote Originally Posted by markosheehan View Post
    It's says that chemistry questions can be posted in this section.
    Yes, that is true ... however, that doesn't mean your chemistry question(s) will get answered in a Math Topics forum.

    I mentioned the Chemistry Help tab to the Chemistry Help forum to give you another avenue to get your questions answered.

    Use it, or don't.
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  9. #9
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    Re: chemistry titration question

    How does this sound:

    "Iron(II) is very susceptible to air oxidation, forming iron(III), under neutral or alkaline conditions but this oxidation is inhibited in the presence of acids. The ammonium iron(II) sulfate solution is made up in dilute acid solution to make it stable towards air oxidation."
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