Using tabulated Ka and Kb values, calculate the pH of the following solutions.
A solution made by mixing 100.00 mL of 1.000 M HOCl with 65.00 mL of 0.900 M NaOH.
Anytime that you have a weak acid (HOCl) and a
strong base (NaOH) mixed together, AND the mols of acid > mols of base added,
then you can safely use the Henderson-Hasselbalch equation.
pka + log(A-/HA)
where A- is the
conjugate base (ion after dissociation)
is the unassociated acid
First, neutralization occurs:
HA + OH- à
H20 + A-
Mols of OH- added =
0.065L * 0.900M = 5.85E-2 mols
Mols of HA before mixing = 0.10000L *
1.000M = 0.1000 mols
After neutralization occurs:
Mols of HA after mixing =
0.1000mols - 5.85E-2 mols =
Mols of A- after mixing = mols of OH- added = 5.85E-2 mols
Plug and chug into the Henderson Hasselbalch eqn
pH = -log(3.5E-8) + log(5.85E-2/4.15E-2)
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