Solving Titration Problems (4.3.2)

Question 1

• In a redox titration, moles of an unknown reductant (or oxidant) are determined
by adding a known amount of a standardized oxidant (or reductant) that reacts with
the unknown stoichiometrically.

Answer 1

• In a redox titration, moles of an unknown reductant (or oxidant) are determined
by adding a known amount of a standardized oxidant (or reductant) that reacts with
the unknown stoichiometrically.

Question 2

• Knowing the stoichiometry of a titration allows for the calculation of the
concentration of an unknown.

Answer 2

• Knowing the stoichiometry of a titration allows for the calculation of the
concentration of an unknown.

Question 3

In a redox titration, moles of an unknown reductant
(or oxidant) are determined by adding a known
amount of a standardized oxidant (or reductant) that
reacts with the unknown stoichiometrically.
For example, cerium(IV) ion (Ce4+) reacts with
iron(II) ion (Fe2+) to form cerium(III) ion (Ce3+) and
iron(III) ion (Fe3+). In this oxidation-reduction
reaction, cerium(IV) ion gains electrons, and is
therefore the oxidant. Iron(II) ion loses electrons,
and is therefore the reductant.
Knowing the stoichiometry of a titration allows for
the calculation of the concentration of an unknown.
Problem: 20.00 mL of an unknown concentration
of FeSO4 is titrated with a 0.107 M solution of
Ce(NH4)2(NO3)6. If 5.72 mL of the cerium solution is
required to reach the equivalence point, what is
the concentration of the iron sulfate?
First, use the balanced chemical equation to
determine the stoichiometry of the reaction between
Ce4+ and Fe2+. In this example, the stoichiometry is
1:1.
Second, determine the number of moles of Ce4+ that
were consumed. This is accomplished by
multiplying the volume of the cerium solution used
(5.72 mL, converted to liters) by the concentration
of the cerium solution (0.107 M).
Since the stoichiometry is 1:1, the moles of Ce4+
consumed equal the moles of Fe2+ originally
present. Dividing moles of Fe2+ by volume of Fe2+
yields concentration of Fe2+, which is the same as
the concentration of FeSO4.

Answer 3

In a redox titration, moles of an unknown reductant
(or oxidant) are determined by adding a known
amount of a standardized oxidant (or reductant) that
reacts with the unknown stoichiometrically.
For example, cerium(IV) ion (Ce4+) reacts with
iron(II) ion (Fe2+) to form cerium(III) ion (Ce3+) and
iron(III) ion (Fe3+). In this oxidation-reduction
reaction, cerium(IV) ion gains electrons, and is
therefore the oxidant. Iron(II) ion loses electrons,
and is therefore the reductant.
Knowing the stoichiometry of a titration allows for
the calculation of the concentration of an unknown.
Problem: 20.00 mL of an unknown concentration
of FeSO4 is titrated with a 0.107 M solution of
Ce(NH4)2(NO3)6. If 5.72 mL of the cerium solution is
required to reach the equivalence point, what is
the concentration of the iron sulfate?
First, use the balanced chemical equation to
determine the stoichiometry of the reaction between
Ce4+ and Fe2+. In this example, the stoichiometry is
1:1.
Second, determine the number of moles of Ce4+ that
were consumed. This is accomplished by
multiplying the volume of the cerium solution used
(5.72 mL, converted to liters) by the concentration
of the cerium solution (0.107 M).
Since the stoichiometry is 1:1, the moles of Ce4+
consumed equal the moles of Fe2+ originally
present. Dividing moles of Fe2+ by volume of Fe2+
yields concentration of Fe2+, which is the same as
the concentration of FeSO4.