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March 30, 2017

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The triation of 50.00 mL of 0.025 00 M MES with 0.100 0 M NaOH. MES is a weak acid with pKa=6.27. Compute Ve, first. Show what happens at the four stages of the titration: Va = 0,2,5,10,10.1,11,12, and 12.2 mL.

I NEED HELP!!!!

  • Chemistry - ,

    Can you calculate volume to get to the equivalence point? Do that first.
    a. First stage: at the beginning.
    .........HA ==> H^+ + A^-
    initial..0.025..0.....0
    change...-x.....x.....x.
    equil...0.025-x..x....x

    Substitute into the Ka expression and solve for x, then convert to pH.

    b. At the equivalence point you have the salt. The hydrolysis of the salt:
    You will need to determine the concn of the salt. That will be (50*0.025/50+Ve)= ?
    .........A^- + HOH ===> HA + OH^-
    initial.. ?.............0.....0
    change..-x..............x.....x
    equil....?-x.............x....x

    Kb for A^- = (Kw/Ka for MES) = (HA)(OH^-)/(A^-)
    Substitute from the ICE chart and solve for x = (OH^-), then convert to pH.

    c. Everything between beginning and the equivalence point.
    mols MES = M x L
    mols NaOH = M x L
    Subtract which will leave an excess of MES PLUS the salt formed. I would use the Henderson-Hasselbalch equation which is pH = pKa + lopg (salt/acid)

    d. Everything after the equivalence point.
    mols EXCESS NaOH/total volume. This will be OH^-, convert to pOH, then to pH.
    Post your work if you get stuck.

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