Student no#: 202003056
Name: Masobeng R.M
Co-workers: kaeane K.K
Day of lab: Friday
Date of lab: 24/03/2023
Submission day: Thursday 06/04/2023
Experiment 3: Determination of the formula, reactions and properties of the iron-oxalate
coordination compound.
AIM:
To determine the iron and oxalate ion content of the 𝐾3 [(𝐶2𝑂4)3] ∙ 3𝐻2 compound by performing
two independent analysis using titration with potassium permanganate solution.
ABSTRACT:
The purpose of the experiment was to determine the iron to oxalate ratio in the compound by
redox titration. This began by preparing the iron coordination compound then directly titrated it
with potassium permanganate. The oxalate was oxidized by the permanganate according to the
equation:
2MnO4- + 5C2O4-2 + 16H+ → 10CO2 + 2Mn+2 + 8H2O
The end-point of titration occurred when the pink colour of the last drop of the permanganate
added persisted for at least about 30 seconds.
On the other part, the samples of the iron coordination compound were first treated with
concentrated sulphuric acid. The concentrated sulphuric acid decomposed the oxalate ion present
in the complex into CO and CO2 according to the equation:
K3 [Fe(C2O4)3] • 3H2O + 6H2SO4 → 3K+ + Fe+3 + 6HSO4 - + 6H2O + 3CO +3CO2
The resulting solution, which now contains Fe+3, is diluted with water and treated with a sample
of zinc which has been amalgamated with a small amount of mercury to increase its surface
reactivity. The zinc quantitatively reduces the Fe+3 to Fe+2 according to the reaction:
2Fe+3 + Zn → 2Fe+2 + Zn+2
Then each solution is tested for complete reduction of Fe+3 and the solution containing Fe+2 ions
is then separated from the zinc amalgam by decantation. The solution is then titrated with
standard potassium permanganate solution to a faint pink endpoint. The reaction with
permanganate is:
5Fe+2 + MnO4- + 8H+ → 5Fe+3 + Mn+2 + 4H2O
Once all the data was collected, it was possible to begin analysis. The first was knowing molarity
of potassium permanganate to get both iron and oxalate ion compositions in the compound.
Stoichiometry was used to find moles of Fe3+ to C2O4-2 ,sample 1; 0.00040 mol to 0.001315mol.
Weight 0.1117g to 0.5785g respectively. Weight percentage 11.17% to 57.85 % respectively.
Sample 2 the number of moles of Fe3+ to C2O42- were found to be; 0.001mol to 0.001325mol.
Weight 0.27925g to 0.5830g. The weight percentage 27.93% to 58.30 % respectively. There was
a ratio of 3.3 moles oxalate to 1 mole iron for sample 1 and sample 2, 1 mole oxalate to 1.3
moles of iron after calculations for both oxalate and iron analysis were completed. Therefore,
when referencing previous lab , it can be concluded that the complex made was actually
𝐾3[𝐹𝑒(𝐶2𝑂4)3] ∙ 3𝐻2𝑂 because the percent weight of oxalate was found for the possible complex.
In conclusion, it was found that moles of Fe3+ to C2O4-2 are; sample 1; 0.00040 mol to
0.001315mol. Weight 0.1117g to 0.5785g respectively. Weight percentage 11.17% to 57.85 %
respectively. Sample 2; 0.001mol to 0.001325mol respectively. Weight 0.27925g to 0.5830g
respectively. Weight percentage 27.93% to 58.30 % respectively. There was a ratio of 3.3 moles
oxalate to 1 mole iron for sample 1 and sample 2, 1 mole oxalate to 1.3 moles of iron after
calculations for both oxalate and iron analysis were completed. When referencing previous lab,
it can be concluded that the complex made was actually 𝐾3[𝐹𝑒(𝐶2𝑂4)3] ∙ 3𝐻2𝑂 because the
percent weight of oxalate was found for the possible complex. The color of Fe3+ was found to
be yellow. And the colour of C2O4-2was colourless.
INTRODUCTION:
Iron and oxalate have marked redox properties so the iron and oxalate ion content of the
𝐾3[𝐹𝑒(𝐶2𝑂4)3] ∙ 3𝐻2𝑂 compound will be determined by using redox titration. The reaction is
heated to just below boiling point and done in acidic condition since it is slow at room
temperature and neutral conditions. The oxalate is oxidized by the permanganate according to the
equation:
2MnO4- + 5C2O4-2 + 16H+ → 10CO2 + 2Mn+2 + 8H2O
Oxalate ions must be eliminated in the complex to have only salt of iron after titration. This is
achieved by decomposing these oxalate ions with use of concentrated sulphuric acid. The
concentrated sulphuric acid decomposed the oxalate ion present in the complex into CO and CO2
according to the equation:
K3 [Fe(C2O4)3] • 3H2O + 6H2SO4 → 3K+ + Fe+3 + 6HSO4 - + 6H2O + 3CO +3CO2
The resulting solution, which now contains Fe+3, is diluted with water and treated with a sample
of zinc which has been amalgamated with a small amount of mercury to increase its surface
reactivity. The zinc quantitatively reduces the Fe+3 to Fe+2 according to the reaction:
2Fe+3 + Zn → 2Fe+2 + Zn+2
Each solution is tested for complete reduction of Fe+3 and the solution containing Fe+2 ions is
then separated from the zinc amalgam by decantation. The solution is then titrated with standard
potassium permanganate solution to a faint pink endpoint. The reaction with permanganate is:
5Fe+2 + MnO4- + 8H+ → 5Fe+3 + Mn+2 + 4H2O
PROCEDURE:
Part a
The analysis for oxalate involves several steps to determine the amount of C2O42- ion in a
complex iron salt sample. First, two separate samples of the salt are weighed to the nearest 0.001
g, each weighing 0.2 g. These samples are then transferred to separate 250 mL flasks, and a few
mLs of 3 M H2SO4 are added to each, followed by dilution to about 75 mL with water. The
flasks are labeled to avoid confusion between the two samples.
Next, a burette is rinsed and filled with standard KMnO4 solution. Each sample is heated to just
below boiling point, and 3 M H3PO4 is added before immediately titrating with the
permanganate solution. The end point of the titration is reached when the pink color of the last
drop of permanganate added persists for at least about 30 seconds. The solutions should not be
discarded at this point as they will be used in the analysis for iron in the next section.
Data for each sample, including initial and final volumes (Vi and Vf) of the permanganate
solution used in the titration, should be recorded in a lab notebook. From this data, the number of
moles, weight, and percentage weight of C2O4 2- ion in the complex salt can be calculated for
each sample. These calculations should be compared with the weight of C2O4 2- calculated from
the accepted formula of the complex ion salt to ensure accuracy.
Overall, this analysis for oxalate provides a quantitative measurement of the amount of C2O4 2ion in a complex iron salt sample. By following the proper procedures and accurately recording
data, researchers can obtain reliable results that can be used for a variety of applications in
chemistry and other fields.
Part b
Analysis for iron involves several steps, which are described below. Firstly, a Zn amalgam is
prepared by weighing about 10 g of granulated zinc into a 100 ml flask and adding about 0.3 g
HgCl2 and 20 mL of 1 M HCl. The mixture is then shaken for several minutes and the excess
solution is poured off, followed by washing the amalgam two or three times with 20-30 mL
portions of water.
Next, to each sample, 6 mL of concentrated H2SO4 is added and the sample is gently heated until
dense white fumes of sulphur trioxide begin to be evolved. This step should be carried out in a
fume hood to ensure safety. 30 mL of water is then added to each sample very slowly to avoid
acid sputtering caused by the evolution of large amounts of heat from the reaction of water with
any residual concentrated H2SO4.
Half of the washed zinc amalgam is then added to each flask, and the flasks are gently heated
and swirled alternatively for 10 minutes. At the end of this time, each solution is tested for
complete reduction of Fe3+ by dipping a stirring rod in the solution and transferring the drop
adhering from the stirring rod tip to a drop of KSCN in the spot tile. This heating and testing step
is repeated until the reddish color of the FeSCN2+ almost fades, indicating complete reduction.
When the reduction is complete, the flasks are cooled under tap water, and each sample is
carefully decanted into a separate clean 250 mL flask. The zinc amalgam is then rinsed with
three 10 mL portions of 3 M H2SO4, with each portion of rinse solution added to the flask
containing the sample solution. 10 mL of concentrated H3PO4 is added to each solution, warmed
up to about 60°C, and immediately titrated with standard KMnO4 solution to a faint pink
endpoint. Finally, the used zinc amalgam is disposed of into a container specially provided for
the purpose, and the data (Vi and Vf) is recorded in the lab notebook.
Part c
To conduct a series of tests on a complex solution, first, a 0.1 M test solution needs to be
prepared. This can be achieved by dissolving 5g of the complex in 100 ml of deionized water.
Once the solution is prepared, it can be used for further testing.
The first test involves taking 1 mL of the green solution and adding 3 drops of 6 M HCl to obtain
solution 2. Then, 3 drops of 0.5 M KSCN are added to solution 2, causing it to turn red (solution
3). To this red solution, 10 drops of 3 M KF are added, which results in the solution becoming
almost colorless (solution 4). Finally, 15 drops of 2 M K2C2O4 are added to solution 4.
In the second test, 1 mL of 0.1 M NaOH is added to 1 mL of solution 1. This produces a brown
precipitate, which is referred to as A, and a colorless solution 6. These two can be separated by
either centrifugation or filtration. The brown solid A is then shaken with 1 mL of 1 M H2C2O4,
while the colorless solution 6 is treated with 1 mL of 0.2 M BaCl2 to obtain precipitate B. After
centrifugation or filtration, the white solid B is treated with 10 drops of 1 M Fe2(SO4)3, which
results in the green solution 1 being obtained again and a white precipitate C.
The third test involves adding 5 mL of 0.2 M BaCl2 to 1 mL of solution 1. This causes a palegreen precipitate, D, to appear, which can be separated by centrifugation or filtration. The palegreen solid D is then treated with 3 mL of distilled water and heated until complete dissolution of
the solid occurs. This produces a solution 7, to which 3 drops of 0.5 M K2SO4 are added,
resulting in the white precipitate C and the green solution 1.
In the fourth test, 1 mL of freshly prepared solution 1 is taken, and 1 drop of 0.1 M K3[Fe(CN)6]
is added to test for Fe2+. Then, 20 mL of solution 1 is placed in a 50-mL beaker and exposed to
light from a flashlight/torch or a 60 W bulb at 15 cm from the surface of the solution. The Fe2+
test is repeated every 90 seconds for 5 minutes with aliquots of 1 mL. The tests are kept in the
test tube rack to observe the progress of the reaction. After 10 minutes of exposure to light, the
Fe2+ test is repeated and compared to the previous ones. Finally, the remaining solution is put
under a mild vacuum, and the observer can observe what happens to the solution.
RESULTS AND CALCULATIONS:
Table 1: Analysis for oxalate
Sample
1
2
Average
Mass[g]
0.200
0.200
0.200
Vi[ml]
0
26.30
13.15
Vf[ml]
26.30
52.80
39.55
Table 2: Analysis for iron
Mass[g]
Vi[ml]
Vf[ml]
Sample 1
Sample 2
Average
0.200
0.00mL
4.00mL
0.200
4.00mL
14.00mL
0.200
2.00mL
9.00mL
Table 3: masses of substances used in analysis of iron
Substances
Zinc granules
HgCl2
10.0149
0.3089
Table 4: results and deduction for analysis of the reactions and properties of the iron-oxalate
complex.
Test
Water + complex
green solution 3 drops 6M
HCl
Solution 2 + 3 drops KSCN
Solution 3 plus 10 drops of
2M KF
Solution 4 + 15 drops of 2M
K2C2O4
observation
A green solution was
formed
Green solution turned
yellow-green(solution 2)
The solution turned
red(solution 3)
The solution turned almost
colourless (SOLUTION4)
Solution turned light green
Solution 1+0.1M NaOH
Brown precipitate was
formed in clear
solution(solution6)
Brown precipitate + 0.1M
H2SO4
Brown precipitate dissolve
and green solution was
formed
Deduction
The solution is more soluble
in hot water
The yellow-green solution
was due to FeCl3
The red solution was due to
Fe(SCN)3
The colourless solution was
due to FeF3
The green solution was due
to [Fe(C2O2)3]. Whe more
of potassium oxalate was
adde the intensity of green
colour decreases
The brown precipitate was
due to Fe(OH)3.
More of the brown
precipitate was formed
when more of the base was
added.
The green solution was due
to [Fe(C2O4)3]3-
Solution 6 + 0.2M BaCL2
White precipitate was
formed in a colourless
solution
White precipitate was
BaC2O4
Balanced Chemical Equations:
1. The oxalate oxidization by the permanganate:
2MnO4- + 5C2O4-2 + 16H+ → 10CO2 + 2Mn2+ + 8H2O
2. Decomposition of the oxalate with concentrated sulphuric acid:
K3 [Fe(C2O4)3] • 3H2O + 6H2SO4 → 3K+ + Fe3+ + 6HSO4 - + 6H2O + 3CO +3CO2
3. Reduction of Fe3+ to Fe2+
2Fe+3 + Zn → 2Fe+2 + Zn+2
4. Titration of Fe2+ with standard potassium permanganate:
5Fe+2 + MnO4- + 8H+ → 5Fe+3 + Mn+2 + 4H2O
A. Analysis of oxalate
Sample 1
Molarity of MnO4 = 0.02M
Volume of MnO4 = Vf-Vi
= 26.30mL-0.00mL
= 26.30ml  0.0263 L
Moles MnO4= [molarity MnO4] [volume MnO4]
= [0.02M] [0.0263 L]
= 0.000526 mol
The oxalate oxidization by the permanganate:
2MnO4- + 5C2O4-2 + 16H+ → 10CO2 + 2Mn2+ + 8H2O
Mole Ratio of MnO4- to C2O4-2 = 2:5 respectively
Therefore stoichiometric ratio in terms of moles:
5
C2O4-2 = [2][0.000526mol]
= 0.001315mol
Mass of C2O4-2 = [moles of C2O4-2 ][molar mass of C2O4-2 ]
= [0.001315mol][88.019g/mol]
= 0.1157 g
𝑚𝑎𝑠𝑠 𝑪 𝑂−2
𝟐 4
Weight of C2O4-2 = 𝑚𝑎𝑠𝑠 𝑠𝑎𝑚𝑝𝑙𝑒
1
=
0.1157𝑔
0.200𝑔
= 0.5785g
𝑚𝑎𝑠𝑠 𝑪 𝑂−2 /
𝟐 4
Percentage weight of C2O4-2 = [𝑚𝑎𝑠𝑠 𝑠𝑎𝑚𝑝𝑙𝑒
][100%]
1
=
0.1157𝑔
0.200𝑔
×100%
= 57.85 %
Sample 2
Molarity of MnO4 = 0.02M
Volume of MnO4 = Vf-Vi
= 52.80mL-26.30mL
= 26.50ml  0.0265 L
Moles MnO4= [molarity MnO4][volume MnO4]
= [0.02M][ 0.0265 L]
= 0.00053 mol
The oxalate oxidization by the permanganate:
2MnO4- + 5C2O4-2 + 16H+ → 10CO2 + 2Mn2+ + 8H2O
Mole Ratio of MnO4- to C2O4-2 = 2:5 respectively
Therefore stoichiometric ratio in terms of moles:
5
C2O4-2 = [2] [ 0.00053mol]
= 0.001325 mol
Mass of C2O4-2 = [moles of C2O4-2 ][molar mass of C2O4-2 ]
= [0.001325 mol][88.019g/mol]
= 0.1166g
𝑚𝑎𝑠𝑠 𝑪 𝑂−2
𝟐 4
Weight of C2O4-2 = 𝑚𝑎𝑠𝑠 𝑠𝑎𝑚𝑝𝑙𝑒
2
=
0.1166𝑔
0.200𝑔
= 0.5830g
𝑚𝑎𝑠𝑠 𝑪 𝑂−2 /
𝟐 4
Percentage weight of C2O4-2 = [𝑚𝑎𝑠𝑠 𝑠𝑎𝑚𝑝𝑙𝑒
][100%]
2
=
0.1166𝑔
0.200𝑔
×100%
= 58.30 %
B. Analysis for iron
Sample 1
Molarity of MnO4 = 0.02M
Volume of MnO4 = Vf-Vi
= 4.00mL-0.00mL
= 4.00 ml  0.004 L
Moles MnO4= [molarity MnO4][volume MnO4]
= [0.02M][0.004L]
= 0.00008 mol
The iron oxidization by the permanganate:
5Fe+2 + MnO4- + 8H+ → 5 Fe3+ + Mn+2 + 4H2O
Mole Ratio of MnO4- to Fe3+ = 1:5 respectively
Therefore stoichiometric ratio in terms of moles:
5
Fe3+ = [1][0.00008]
= 0.0004 mol
Mass of Fe3+ = [moles of Fe3+ ][molar mass of Fe3+ ]
= [0.0004mol][55.85g/mol]
= 0.02234g
𝑚𝑎𝑠𝑠 𝑭𝒆𝟑+
Weight of Fe3+ = [ 𝑚𝑎𝑠𝑠 𝑠𝑎𝑚𝑝𝑙𝑒 1]
=
0.02234𝑔
0.200𝑔
= 0.1117 g
Percentage weight of Fe3+
𝑚𝑎𝑠𝑠 𝑭𝒆𝟑+
= [ 𝑚𝑎𝑠𝑠 𝑠𝑎𝑚𝑝𝑙𝑒 1]× 100%
=
0.02234𝑔
0.200𝑔
× 100% = 11.17%
Sample 2
Molarity of MnO4 = 0.02M
Volume of MnO4 = Vf-Vi
= 14.00mL-4.00mL
= 10.00mL  0.01 L
Moles MnO4= [molarity MnO4][volume MnO4]
= [0.02M][0.01L]
= 0.0002 mol
The iron oxidization by the permanganate:
5Fe+2 + MnO4- + 8H+ → 5 Fe3+ + Mn+2 + 4H2O
Mole Ratio of MnO4- to Fe3+ 1:5 respectively
Therefore stoichiometric ratio in terms of moles :
5
Fe3+ = [1][0.0002]
= 0.001mol
Mass of Fe3+ = [moles of Fe3+ ][molar mass of Fe3+ ]
= [0.001mol][55.85g/mol]
= 0.05585g
𝑚𝑎𝑠𝑠 𝑭𝒆𝟑+
Weight of Fe3+ = [ 𝑚𝑎𝑠𝑠 𝑠𝑎𝑚𝑝𝑙𝑒 2 ]
=
0.05585𝑔
0.200𝑔
= 0.27925g
Percentage weight of Fe3+
𝑚𝑎𝑠𝑠 𝑭𝒆𝟑+
= [ 𝑚𝑎𝑠𝑠 𝑠𝑎𝑚𝑝𝑙𝑒 2]× 100%
=
0.05585𝑔
0.200𝑔
× 100% = 27.93%
Ratio of the number of moles of C2O4-2 to the number of moles of Fe3+ :
-divide each mole with the smallest number of moles
Sample 1
C2O4-2 = [0.001315 mol/0.0004mol]
=3.3
C2O4-2: Fe3+
3.3:1
Fe3+ = [0.0004mol/0.0004mol]
=1
Sample 2
C2O4-2 = [0.001 mol/0.001 mol]
Fe3+ = [0.001325/0.001mol]
=1
=1.3
C2O4-2: Fe3+
1:1.3
There is a ratio of 3.3 moles oxalate to 1 mole iron.
Analysis C
Table 5: identification of solutions and precipitates
Solution
1
2
3
4
5
6
7
Identity
K3[Fe(C2O4)3]
FeCl3
Fe(SCN)3
FeF3
K3[Fe(C2O4)3]
NaC2O4
K3[Fe(C2O4)3]
Precipitate
A
B
C
D
Identity
Fe(OH)3
BaC2O4
BaSO4
Ba3[Fe(C2O4)3]
DISCUSSION:
Once all the data was collected, it was possible to begin analysis. The first was knowing molarity
of potassium permanganate to get both iron and oxalate ion compositions in the compound.
Stoichiometry was used to find moles of Fe3+ to C2O4-2 ,sample 1; 0.00040 mol to 0.001315mol.
Weight 0.1117g to 0.5785g respectively. Weight percentage 11.17% to 57.85 % respectively.
Sample 2 the number of moles of Fe3+ to C2O42- were found to be; 0.001mol to 0.001325mol.
Weight 0.27925g to 0.5830g. The weight percentage 27.93% to 58.30 % respectively. There was
a ratio of 3.3 moles oxalate to 1 mole iron for sample 1 and sample 2, 1 mole oxalate to 1.3
moles of iron after calculations for both oxalate and iron analysis were completed. Therefore,
when referencing previous lab , it can be concluded that the complex made was actually
𝐾3[𝐹𝑒(𝐶2𝑂4)3] ∙ 3𝐻2𝑂 because the percent weight of oxalate was found for the possible complex.
The large sources of error in this experiment trials could be attributed to many different factors.
These factors include inconsistent heating while creating each complex.
CONCLUSION:
In conclusion, it was found that moles of Fe3+ to C2O4-2 are; sample 1; 0.00040 mol to
0.001315mol. Weight 0.1117g to 0.5785g respectively. Weight percentage 11.17% to 57.85 %
respectively. Sample 2; 0.001mol to 0.001325mol respectively. Weight 0.27925g to 0.5830g
respectively. Weight percentage 27.93% to 58.30 % respectively. There was a ratio of 3.3 moles
oxalate to 1 mole iron for sample 1 and sample 2, 1 mole oxalate to 1.3 moles of iron after
calculations for both oxalate and iron analysis were completed. When referencing previous lab,
it can be concluded that the complex made was actually 𝐾3[𝐹𝑒(𝐶2𝑂4)3] ∙ 3𝐻2𝑂 because the
percent weight of oxalate was found for the possible complex. The color of Fe3+ was found to
be yellow. And the colour of C2O4-2was colourless.
References:
1- Muller H., Iron oxalate, https://www.mdpi.com, (accessed March 25, 2023)
2- Inorganic Chemistry, http://www.saylor.org/courses/chem107/ (accessed March 25, 2023)
3- Christine L., Project 4 Final, https://www.studylib.com, (accessed March 25, 2023)