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March 27, 2017

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3. A chemistry student makes up a 0.10 M solution of NaF(aq) and finds the pH to be 8.09.
a. Explain why the presence of F- in this solution affects the pH.
b. Write out the acid/base equilibrium equation for the reaction of F- with water.
c. Use the measured pH value to solve for the Kb of this reaction.
d. Calculate the product of your calculated Kb and the Ka of HF (found on the table) and explain the familiarity of this number.

  • Chemistry - ,

    I will do b and c and from that work you can do a and d.
    b.
    .........F^- + HOH ==> HF + OH^-
    initial.0.1M...........0......0

    c.
    What pH value did you get? I need a number; let's call that y = OH and and you can substitute the value you measured it to be after converting from pH.
    ..........F^- HOH ==> HF + OH^-
    initial..0.1..........0.....0
    change...-y...........y.....y
    equil....0.1-y.........y.....y

    Kb for F^- = (HF)(OH^-)/(F^-)
    You know HF from the measured pH.
    You know OH from the measured pH.
    You know F^- = 0.1-y
    Solve for Kb for F^-

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