Posted by Lance on Wednesday, April 11, 2012 at 7:03pm.
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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