1. Limited time only! Sign up for a free 30min personal tutor trial with Chegg Tutors
    Dismiss Notice
Dismiss Notice
Join Physics Forums Today!
The friendliest, high quality science and math community on the planet! Everyone who loves science is here!

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
  5. Feb 29, 2008 #4


    User Avatar
    Homework Helper
    Education Advisor
    Gold Member

    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


    User Avatar
    Science Advisor
    Homework Helper
    Gold Member

    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)..."?
Share this great discussion with others via Reddit, Google+, Twitter, or Facebook