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Aqueous solutions and whether they are acidic/basic/neutral

  1. Apr 10, 2009 #1

    ~christina~

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    This isn't a homework question but a general question which I should know the answer to but am not sure.

    If you have a basic/acidic compound and add it to water to form an aqueous solution, the water should turn basic/acidic respectively, right? no exception?

    Thank you
     
  2. jcsd
  3. Apr 11, 2009 #2

    Borek

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    Define basic/acidic compound.
     
  4. Apr 11, 2009 #3

    ~christina~

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    Lewis Base/Acid
    Acid- accepts e- pair
    Base- donates e- pair

    Bronsted-Lowry Acid/Base
    Acid -donates H+ ion
    Base- accepts H+ ion
     
  5. Apr 11, 2009 #4

    Astronuc

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    I think Borek was thinking in the context of an aqueous solution.

    How would one characterize HBr or H2SO4, NaAc (Ac = acetate), or BF3, anhydrous, i.e. pure and out of water?

    BF3 is interesting because it is used in gaseous neutron detectors, particularly with B enriched in B-10.
     
  6. Apr 11, 2009 #5
    Borek is right.
    Let's make another example: acetic acid. Is it a base or an acid? Would you say acid? With respect to what? If your answer is "with respect to water" then your question is meaningless...
    In general, every substance can be acid or base. Acetic acid ( [tex]CH_3COOH[/tex] ) for example is a base with respect to [tex]H_2SO_4[/tex] . If you mix them, you will find [tex]HSO_4^-[/tex] and [tex]CH_3COOH_2^+[/tex].
     
  7. Apr 11, 2009 #6

    ~christina~

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    Well, this would be comparing the relative strength of basicity/acidity of one compound to another...or the relative willingness of one compound to accept vs give away a H+ ion. (ex. H20 can gain a H+ to become H30+ or it can loose a H+ to have OH- ion)
     
  8. Apr 12, 2009 #7
    Yes, so, acetic acid, for example, can be considered a base. If you put it on water how will the solution become, acidic or basic? You see that your question doesn't have a definite solution until you give a definition of acid or base, that is, acid or base with respect to something.
     
  9. Apr 15, 2009 #8

    ~christina~

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    I understand. It's just that a professor asked me this question and did not ask me this with respect to anything. I do suspect that it would be respect to water, if you're placing it in water?
     
  10. Apr 16, 2009 #9
    Usually it's so. Then your question has an obvious answer.
    As you see, it really depends on how your professor define a "basic/acidic" compound. It could even define as "acidic" a compound which, in water solution, reacts (almost) quantitatively with a strong base, but a buffer compound can do it as well, and if you dissolve a buffer compound in water the solution can become acidic, basic, neutral...
     
    Last edited: Apr 16, 2009
  11. Apr 16, 2009 #10

    ~christina~

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    Yes. I understand what you're saying. It was just that I was probably thinking about it a little too simply.

    Thanks lightarrow
     
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