Chemistry question: CHEM 251

Chemistry question: CHEM 251

1) (10 points) A mixture is made of two weak bases. A 15.00 mL aliquot of the base
mixture is analyzed by titration with a 0.140 M strong acid. The resulting titration
data is plotted in the graph below. Use this graph to determine the answers to the
questions in the table below

2) (15 points) A 25.00 mL aliquot of a solution
containing 40.00 mM phosphoric acid is
titrated with a 0.200 M LiOH titrant. Determine
the pH of the solution during the course of the
titration at the volumes indicated in the table to
the right.

3) (12 points) A 30.00 mL solution containing 45.00
mM iodine and buffered to pH 8.94 is titrated
with a solution of Pb4+. The concentration of
lead(IV) in the titrant is 75.00 mM. The cell
potential is monitored with a platinum wire
cathode, and a S.C.E. (0.241 V) anode as the
reference electrode. Determine what potential
will be measured for each of the titration
volumes listed in the table to the right.
Use the half reactions below to determine the cell potentials.
Pb4+ + 2e– ⇌ Pb2+ E° = 1.69 V
IO3– + 3H2O + 6e– ⇌ I– + 6OH– E° = 0.269 V



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