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Calculate the volume of 0.05 M NaOH which must be added to 100 cm3 of 0.05 M methanoic acid to obtain a buffer of pH 4.23.�(Ka for methanoic acid = 1.77 x 10-4)

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asked by Teagan
  1. Use the Henderson-Hasselbalch equation.
    millimols HCOOH = mL x M = 100 x 0.05 = 5

    ......HCOOH + NaOH ==> HCOONa + H2O
    I.......5.......0........0........0
    add.............x................
    C.......-x.....-x........+x
    E.......5-x......0........x
    x = base
    5-x = acid

    Substitute into the HH equation.
    pH = pKa + log (base)/(acid)

    4.23 = pKa + log (x)/(5-x)
    Solve for x which is millimols NaOH that must be added. Then millimols NaOH = mL x M. You have mmols and M, solve for mL.

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    posted by DrBob222

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