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General Chemistry

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How many milliliters of 0.5M NaOH must be added to 200 mL of 0.1M NaH2PO4 to make a
buffer solution with a pH of 6.9?

  • General Chemistry -

    200 mL x 0.1M H2PO4^- = 20 millimols.
    ?mL x 0.5M NaOH =?

    ........H2PO4^- + OH^- ==> HPO4^- + H2O
    I.......20........0..........0........0
    add...............x...................
    C.......-x.......-x...........x
    E.......20-x......0...........x

    pH = pK2 + log(base)/(acid)
    Substitute into HH equation the E line from the ICE chart above and solve for x = millimoles OH needed.
    Then M = millimols/mL. You know millimoles and M, solve for mL.

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