EXPERIMENT 2
Synthesis of Potassium Tris(oxalato)ferrate(III) Trihydrate
Objective:
Potassium tris(oxalato)ferrate(III) trihydrate [K
3
Fe(C
2
O
4
)
3
·3H
2
O] will be synthesized in a two-
step process and the actual, theoretical, and percent yields of this compound will be determined.
In addition, the number of waters of hydration will be confirmed by gravimetric analysis.
Introduction:
A chemical synthesis is the use of one or more chemical reactions to bring about the construction
of a desired chemical product or products. The reasons for carrying out a chemical synthesis are
varied. It might be the production of a useful substance not found in nature, plastics, for example,
or the production of a substance found in nature but difficult or expensive to isolate in large
quantities, such as ammonia. Then again, it might be the desire to create a substance with new,
useful properties, say, a new medication. Whatever the motivation for the synthesis, maximizing
the conversion of reactants to products is always a priority.
In this experiment, you will synthesize the compound potassium tris(oxalato)ferrate(III)
trihydrate [K
3
Fe(C
2
O
4
)
3
·3H
2
O] in a two-step process. The first step involves the reaction of
ferrous ammonium sulfate hexahydrate [Fe(NH
4
)
2
(SO
4
)
2
·6H
2
O] with oxalic acid (H
2
C
2
O
4
):
4 2
2
2
2
(Pale green)
Fe(NH
4
)
2
(SO ) ·6H O(
s
) + H C O
4
(
aq
)
→
FeC
2
O
4
·2H
2
O(
s
) + (NH
4
)
2
SO
4
(
aq
) + H
2
SO
4
(
aq
) + 4H
2
O(
l
)
(1)
(Yellow)
Where applicable, the colors of reactants and products are indicated in parentheses below their
molecular formula.
The iron(II) oxalate dihydrate (FeC
2
O
4
·2H
2
O) produced in the Reaction (1) will be separated
from the other products by decantation. In the second step, the iron(II) oxalate dihydrate will be
converted to potassium tris(oxalato)ferrate(III) trihydrate [K
3
Fe(C
2
O
4
)
3
·3H
2
O] through reaction
with oxalic acid, hydrogen peroxide (H
2
O
2
), and potassium oxalate (K
2
C
2
O
4
):
2 FeC
2
O
4
·2H
2
O(
s
) + H
2
C
2
O
4
(
aq
) + H
2
O
2
(
aq
)
+ 3 K
2
C
2
O
4
(
aq
)
→
(Yellow)
2 K
3
Fe(C
2
O
4
)
3
·3H
2
O(
s
)
(2)
(Green)
The potassium tris(oxalato)ferrate(III) trihydrate crystals then are separated from solution by
vacuum filtration.
Your objective is to prepare as great a yield of potassium tris(oxalato)ferrate(III) trihydrate as
possible. To measure the effectiveness with which this objective is met, you will calculate the
percent yield:
100
yield
l
theoretica
ield
y
actual
yield
Percent
×
=
(3)
2 – 1
Experiment 2: Synthesis of Potassium Tris(oxalato)Ferrate(III) Trihydrate
The theoretical yield is the calculated maximum amount of product that might be obtained under
ideal conditions from the reactants. In an experiment, the theoretical yield is seldom, if ever,
reached. In this experiment, the theoretical yield is the maximum number of grams of product
[K
3
Fe(C
2
O
4
)
3
·3H
2
