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March 28, 2017

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Ascorbic acid is a weak organic acid also known as vitamin C. A student prepares a 0.20 mol/L aqueous solution of ascorbic acid and measures its pH as 2.40. Based on this evidence, what is the Ka of ascorbic acid?

  • chemistry - ,

    Based on what I can find on the internet, ascorbic acid is a monoprotic acid. If that is so, then let's call ascorbic acid HC.
    Then HC ==> H^+ + C^-

    Ka = ((H^+)(C^-)/(HC)
    If pH = 2.40, then (H^+) = 0.00398/
    (C^-) is the same.
    (HC) = 0.2 = 0.00398
    Plug in the Ka expression and solve for Ka. I get a little over 8 x 10^-5 which gives a pKa of 4.09 which isn't far from the pKa listed in my quant book of 4.17.

  • chemistry - ,

    Thank you! Umm...Whats a quant book? A book read by extraterrestrials??:P

  • chemistry - ,

    Quantitative analysis chemistry book

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