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Henderson hasselback equation

  1. Dec 6, 2012 #1
    1. The problem statement, all variables and given/known data

    . You have solutions of 0.200 M HNO2 and 0.200 M KNO2 (Ka for HNO2 = 4.00 × 10–4). A buffer of pH 3.000 is needed. What volumes of HNO2 and KNO2 are required to make 1 liter of buffered solution?
    A) 500 mL of each
    B) 286 mL HNO2; 714 mL KNO2
    C) 413 mL HNO2; 587 mL KNO2
    D) 714 mL HNO2; 286 mL KNO2
    E) 587 mL HNO2; 413 mL KNO2


    2. Relevant equations

    pH=pKa+log([A]-/[HA])

    3. The attempt at a solution

    3=3.4+log([A-]/[HA])
    -.4=log([A-]/[HA])
    10^-.4
    .398=[A-]/[HA]
    I get confused conceptually of what to do after this. I know I need .398M of conj base for every 1M of acid
     
  2. jcsd
  3. Dec 7, 2012 #2

    Borek

    User Avatar

    Staff: Mentor

    This is one equation. The other is

    [tex]V_{A^-} + V_{HA} = 1L[/tex]

    You need to combine volume with concentration - and you will have two equations in two unknowns. Just solve.
     
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