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Chemistry

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You want to make 1000 ml of an 0.1 M HA buffer so that the pH=pKa of HA. To make this buffer you need to add ____ HA and ____ mL of 1M NaOH and then add enough water to give 1000 mL. HA is a weak acid.

  • Chemistry -

    pH = pKa + log{[A-]/[HA]}
    or
    pH = pKa + log{[NaA]/[HA]}
    if pH = pKa, then {[log{[NaA]/[HA]} = 0
    or [NaA] = [HA]
    The reaction between NaOH and HA is:
    NaOH + HA --> NaA + H2O
    Since we start with no NaA, we must add enough NaOH so that [NaA] = [HA]
    That happens when we neutralize HALF of the HA by using NaOH. The mole ratio of NaOH added to HA is 1 to 2 or 1/2.
    I gave you most of the solution of the problem. You should be able to finish it on your own.

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