Chemistry

What is the pH of a 0.02M solution of potassium benzoate solution ( K+ -OOCC6H5). The pka of benzoic acid is 4.19. (Write answer to the hundredths place)

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asked by Delilah
  1. Let's call benzoic acid HBz so potassium benzoate is KBz. It is the Bz^- that is hydrolyzed and the pH is determined by that hydrolysis.
    ................Bz^- + HOH ==> HBz + OH^-
    I..............0.02M.....................0.............0
    C..............-x...........................x..............x
    E..............0.02-x....................x...............x

    Kb for Bz^- = (Kw/Ka for HBz) = (HBz)(OH^-)/(Bz^-)
    Plug in Kw, Ka(from pKa), the E line for HBz, OH^-, Bz^- and solve for x = (OH^-) and convert to pH. Post your work if you get stuck.

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