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I need some help in this question please check what i have done

  1. Mar 20, 2013 #1
    1. The problem statement, all variables and given/known data
    A 1.00dm3 buffer sollution contains 0.5 mol of ethanoic acid and 1.00 mol sodium ethanoate.

    CH3COOH: Ka= 1.8x10-5

    Calculate pH of solution
    Calculate change in pH when 1cm3 of 1M HCl is added
    Calculate change in pH when 2cm3 of 1.5M KOH is added

    2. Relevant equations

    pH=pKa + log [A-/HA]


    3. The attempt at a solution

    pH=pKa + log [A-/HA]

    So pH= 4.7 + log [1/0.5] (I changed Ka to pKa)

    pH=5.046

    Is that ok?


    The next part is confusing


    A- + HCl → HA + Cl-

    Initial conc.
    A-= 1M
    HCl =(What do i write for HCl conc)
    HA= 0.5
     
  2. jcsd
  3. Mar 20, 2013 #2

    Borek

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    Staff: Mentor

    1st part is OK.

    For the second and third simply assume reaction (A- protonation or HA neutralization) went to completion and concentrations can be calculated from a simple stoichiometry. This is not 100% accurate, but works in most cases.
     
  4. Mar 20, 2013 #3

    epenguin

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    Homework Helper
    Gold Member

    For first part doesn't [A-]/[HA] = 1?
     
  5. Mar 20, 2013 #4

    Borek

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    Staff: Mentor

    Why? Questions states explicitly 1 mole of A- and 0.5 mole of HA.
     
  6. Mar 20, 2013 #5

    epenguin

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    Gold Member

    Ah yes I had hastily read it for totals of all forms. :blushing:
     
  7. Mar 30, 2013 #6
    thank you very much i figured it out
     
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