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Homework Help: Acid-Base solutions and their effectiveness for deprotonation of NH4+

  1. Feb 29, 2008 #1
    Consider the following solutions and their respective pH values. Which substance would be effective(K>1) for the deprotonation of NH4+ ?
    0.1 M A, pH = 6.85
    0.1 M B, pH = 7.22
    0.1 M C, pH = 8.34
    0.1 M D, pH = 11.88

    1) A
    2) B
    3) C
    4) D
    5) none are effective

    If the reaction to be effective
    doesn't Strong acid have to react with strong base?
    since NH4+ is strong acid, I thought it should react with the strongest
    base among the four substances,
    so i chose D, which has the highest pH value.

    Is it right, or am I doing something wrong here?
     
    Last edited: Feb 29, 2008
  2. jcsd
  3. Feb 29, 2008 #2
    oh.. NH4+ is not a strong acid..
    how do I approach this problem then?

    If K>1, net direction is right,
    then shouldn't the reactants be stonger acid and stronger base?
     
    Last edited: Feb 29, 2008
  4. Feb 29, 2008 #3
    anyone?????????
     
  5. Feb 29, 2008 #4

    symbolipoint

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    Dissociation of ammonium as an acid is weak; I would guess the choice D is the strongest base allowed for you and that would be most effective in deprotonating the ammonium ion. I say it is the strongest base there because all of your choices are 0.1 Molar; and D has the highest pH (therefore most alkaline).
     
  6. Mar 2, 2008 #5
    i thought NH4+ would be a strong acid. NH3 is a weak base, it's conjugate acid, NH4+ should then be strong.

    but you still need the strongest base..... therefore D
     
  7. Mar 3, 2008 #6

    chemisttree

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    Why do you think you were given the pH at a particular concentration? Have you studied the concept of pKa? What 'K' was referred to in the question "...(K>1)..."?
     
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