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Homework Help: Very Urgent: Need Help With Buffers

  1. Mar 9, 2008 #1
    Very Urgent: Need Help With Buffers!!!

    I have a test coming up on Tuesday and I have no idea how to do buffers, I don't understand what Value of the Ka we are suppose to use from the chart. I get the equation a little bit: [H+]= Ka x moles HB/moles of B-

    I am very lost please help!!!!
     
  2. jcsd
  3. Mar 9, 2008 #2

    symbolipoint

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    What? Your problem description and question are poor. What are your knowns and what are you unknowns?
     
  4. Mar 10, 2008 #3
    ok.... i'll try to help you out a bit....

    you should know that buffers resist drastic change in pH.

    basically, the H+ ion concentration in a buffer solution is:

    Ka * [acid] / [salt]

    or for an alkaline buffer

    Kb * [alkali] / [salt]


    [acid] would mean the concentration of the acid in mol/dm3

    if you use ethanoic acid and sodium ethanoate as the buffer, then H+ concentration is

    dissociation constant of ethanoic acid * concentration of ethanoic acid / concentration of sodium ethanoate

    the question will usually ask you about the pH of the buffer. to get the pH:

    pH = -lg [H+]
     
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