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a buffer composed of 0.50mol acetic acid and 0.50mol sodium acetate is diluted to a volume of 1.0L. The pH of the buffer is 4.74. How many moles of NaOH must be added to the buffer solution to increase its pH to 5.74?

  • chemistry -

    I assume you are using pKa = 4.74 so that
    pH = 4.74 + log 0.5/0.5 =
    = 4.74 + log 1 = 4.74 + 0 = 4.74.
    If we call acetic acid HAc and the acetate ion (the base) Ac, then

    To make the pH 5.74 we calculate the B/A as follows:
    5.74 = 4.74 + log B/A
    You can go through the calculation but you should end up with (Ac)/(HAc) = 10

    Then we write the equation
    HAc + NaOH = NaAc + H2O
    HAc = 0.5 to start
    Ac = 0.5 to start.
    We add x moles NaOH.
    The HAc after the reaction will be 0.5 - x and the Ac will be 0.5+x
    Just plug those values into the
    (Ac)/(HAc) = 10 and solve for x.
    I always like to put that value in and resolve the equation to see if I get 5.74.
    Post your work if you get stuck.

  • chemistry -

    thanks for your help, it worked out :)

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