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Calculate the volume of .300 M NaOH needed to prepare a pH=3.50 buffer with 250ml of .075M HF solution. pKa (HF) = 3.15

  • Chem -

    You have 250 mL x 0.075M = 18.75 mmoles HF.
    ........HF + NaOH ==> NaF + H2O
    initial.18.75..0.......0......0
    add.............x................
    change..-x.....-x......+x.....+x
    equil..18.75....0........x.....x

    pH = pKa + log [(base)/(acid)]
    3.50 = 3.15 + log(x/18.75-x)
    Solve for x which gives millimoles, then
    mmoles = mL x M
    You know mmoles and M, solve for mL of the 0.3M NaOH to add.

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