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Thread: chemistry base/acid question

  1. #1 chemistry base/acid question 
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    I'm confused about something.
    I have a chemistry test soon, and I'm practicing, but the answer given by the book about a base/acid reaction seems to me to be wrong.

    the question is: what happens if you put HCl in water with NaF
    The book says this:
    HCl + H2O --> H3O+ + Cl-
    then: F- + H3O+ ---> H2O + HF

    I have the first part as wel, but the second part is wrong, right?
    Shouldn't it be:
    F- + H3O+ ---> H2O + HF
    ................ <---

    Because HF itself is a weak acid, it should be a reaction that moves to an equilibrium, right?

    I live in the netherlands so i don't know the english terminology perfectly, but it says in my book that H3O is a strong acid, and therefore there will not be an equilibrium, but all F-'s will react with H3O+.

    It might be that my book is simplifying it, because we're not supposed to do these calculations yet.


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  3. #2  
    Moderator Moderator AlexP's Avatar
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    Your answer seems correct to me. I agree, perhaps the book is just simplifying.


    "There is a kind of lazy pleasure in useless and out-of-the-way erudition." -Jorge Luis Borges
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  4. #3  
    Reptile Dysfunction drowsy turtle's Avatar
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    Quote Originally Posted by questioner1
    Because HF itself is a weak acid, it should be a reaction that moves to an equilibrium, right?
    Actually HF is a very strong acid. Realistically, at standard pressure and temperature the HF molecule would never actually form - dissociation would be essentially 100%.

    You are right to say there should be an equilibrium, by the way. It's just that the equilibrium would be shifted so much to the left that the HF molecule would never really form.
    "The major difference between a thing that might go wrong and a thing that cannot possibly go wrong is that when a thing that cannot possibly go wrong goes wrong it usually turns out to be impossible to get at or repair." ~ Douglas Adams
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  5. #4  
    Forum Masters Degree Twit of wit's Avatar
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    Quote Originally Posted by drowsy turtle
    Actually HF is a very strong acid. Realistically, at standard pressure and temperature the HF molecule would never actually form - dissociation would be essentially 100%.
    HF is a weak acid.
    http://en.wikipedia.org/wiki/Hydrofluoric_acid
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  6. #5  
    Reptile Dysfunction drowsy turtle's Avatar
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    Oh, fair enough. I would have thought from its polarity that it would be a very strong acid.
    "The major difference between a thing that might go wrong and a thing that cannot possibly go wrong is that when a thing that cannot possibly go wrong goes wrong it usually turns out to be impossible to get at or repair." ~ Douglas Adams
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  7. #6  
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    Quote Originally Posted by drowsy turtle
    Oh, fair enough. I would have thought from its polarity that it would be a very strong acid.
    It's so polar that it forms fairly strong hydrogen bonds with water and with other HF molecules, which helps stabilize it.
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