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Homework Help: Conjugate bases

  1. Mar 24, 2010 #1
    1. The problem statement, all variables and given/known data
    Indicate the conjugate bases of the following:

    NH2-
    NH2-

    2. Relevant equations



    3. The attempt at a solution
    This is the only information given. Can I assume that these species react with water? The ionic signs indicate that they are bases, but are they the conjugate bases?
     
  2. jcsd
  3. Mar 25, 2010 #2

    Borek

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    Staff: Mentor

    What are the definitions of acid and conjuagte base? Can you write acid-base reaction equation involving one of given ions as a reactant and the other as a product?

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    methods
     
  4. Mar 28, 2010 #3
    When species donates a proton, it becomes the conjugate base; when a species gains a proton, it becomes a conjugate acid...

    NH2- + H2O -> NH3 + OH-


    NH2- becomes a conjugate acid
     
  5. Mar 28, 2010 #4
    What does [tex]NH{_2}{^-}[/tex] become when it donates a proton?
     
  6. Mar 28, 2010 #5
    nh ?
     
  7. Mar 28, 2010 #6
    Close, but still missing something.

    What will the charge be?
     
  8. Mar 28, 2010 #7
    negative
     
  9. Mar 28, 2010 #8
    So is the conjugate base of NH2- N3-?
     
  10. Mar 28, 2010 #9

    Borek

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    Staff: Mentor

    No, acid and conjugate base must differ by exactly one proton. And PhseShifter didn't ask about positive/negative, but about exact value. You wrote nh (meaning NH) - but what is the exact charge?

    --
    methods
     
  11. Mar 28, 2010 #10
     
  12. Mar 28, 2010 #11

    Borek

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    Staff: Mentor

    Oops, sorry, somehow I missed track of hydrogens and charge :blushing:

    That was right. I misread it as NH2-, not NH2-.

    Still, nh was wrong - should be NH2-. Treat my mistake as a warning why you should never ignore capitalization and charge - it adds to the confusion.

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  13. Mar 28, 2010 #12
    I will, thank you so much for all your help and patience.
     
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