LABORATORY REPORT
CHM361
ANALYSIS OF COORDINATION COMPOUND K3[Fe(C2O4)3].
3H2O
NAME
: SITI NUR WATIQAH BTE ADILAH
STUDENT ID : 2018275972
GROUP
: AS1205A1
CRITERIA
FUL
L
Procedure
2%
Results / Data / Observation (Datasheet)
2%
Data Analysis / Justification / Validation
4%
Question
2%
Discussion
2%
Conclusion
1%
Format
2%
Data Sheet EXP 1
5%
Total
20%
OBTAINED
1.0 OBJECTIVE
-To synthesis a coordination compound, potassium tris (oxalato) ferrate(III) Trihydrate under
carefully controlled conditions.
- To standardize the Potassium Permanganate Solution
- To determine the percentage of ligands in K
! 3 [Fe(C2O4 )3] ∙ 3H2O
2.0 INTRODUCTION
Coordination compound is a compound consisting of a central metal ion chemically bound by a
coordinate covalent bond to one or more atoms or groups of atoms known as ligands. Potassium tris
(oxalato) ferrate (III) is a metal complex of iron with three oxalate ligands C2O42− bonded to every
central metal atom. These ligands are binds to the metal atom at two different places. It has a
chemical formula of K3 [Fe(C2O4 )3] ∙ 3H2O . The structure is also 3 dimensional structure that is
proposed in figure 1.
In experiment 2, , to synthesis a coordination compound, potassium tris (oxalato) ferrate(III)
Trihydrate, this compound will be synthesised by adding Oxalic acid to ferrous ammonium
sulphate hexahydrate Fe(NH4 )2(SO4) ∙ 6H2O under acidic conditions. This will then form
2
iron(II) Oxalate FeC2O4with a yellow precipitate which is then, added to Potassium Oxalate
K2C2O4 and hydrogen peroxide. Lastly a synthesised product is formed.
Fe(NH4 )2(SO4) ∙ 6H2O (aq) + H2C2O4 (aq)
2
FeC2O4 + K2C2O4 ∙ H2O+H2O2
Fe(OH3) + H2O2 + K2C2O4
FeC2O4 (s) + … etc ——-> (1)
Fe(OH3) (s) + …etc
———> (2 and 3)
K3 [Fe(C2O4 )3] ∙ 3H2O (aq) +… etc
———> (4)
Next, in experiment 3, to determine the percentage of ligands in K3 [Fe(C2O4 )3] ∙ 3H2O, the
coordination compound that is used in this experiment is the compound that has been synthesised
from experiment 2 , which is potassium tris (oxalato) ferrate(III) trihydrate. This compound will
then be titrated with standard potassium permanganate solution.
In this session, two parts of experiment are performed. The titration process takes place in both
part. In part A, the potassium permanganate solution is standardised. This part is important in order
to calculate the molarity of the potassium permanganate solution. Later on, the potassium
permanganate solution will be used as the titrant for part B.
In part B, the titration process for the coordination compound that has been prepared in previous
experiment are performed. The compound is potassium tris (oxalato) ferrate (III) trihydrate. This
compound is titrated with standard potassium permanganate solution.
This experiment also required the percentage of ligands in the coordination compound, thus it
needed to be calculated. The molarity of the Potassium permanganate solution that acts as the titrant
in part B needed to be calculated too, as well as the molarity for the coordination compound which
later being converted its form from solid to solution by adding sulphuric acid to its solution.
3.0 APPARATUS
3.1 Balance
3.2 125 mL Erlenmeyer flask
3.3 Measuring cylinder, 50 mL (2 pieces)
3.4 Beaker, 400 mL
3.5 Glass rod
3.6 Ice bath
3.7 Bunsen burner
3.8 Tripod stand
3.9 Thermometer
3.10 Buchner Funnel
3.11 Vacuum filtration apparatus
3.12 Filter paper
3.13 Beakers ( two mL, one 250 mL)
3.14 Volumetric flask (250 mL)
3.15 Storage bottle( 250 mL)
3.16 Pipette (20 mL)
3.17 Pipette filler
3.18 Burette and stand
3.19 Filter funnel
3.20 Conical flask ( 250 mL)
4.0 CHEMICALS
4.1 Ferrous Ammonium Sulphate Fe(NH4 )2(SO4) ∙ 6H2O
2
4.2 0.5 M oxalic acid , H2C2O4 (aq)
4.3 1M potassium oxalate monohydrate K2C2O4 ∙ H2O (aq)
4.4 3M sulphuric acid H2 SO4
4.5 6% hydrogen peroxide , H2O2
4.6 Ethanol
4.7 1:1 ethanol/water solution
4.8 Deionised water
4.9 Potassium permanganate solution , K MnO4 0.02M (300mL)
4.10 Oxalic acid H2C2O4 ∙ 2H2O , 0,05 M (250 mL)
4.11 sulphuric acid H2 SO4 1M (250 mL)
4.12 Complex compound
4.13 K3 [Fe(C2O4 )3] ∙ 3H2O
5.0 PROCEDURE
SYNTHESIS OF POTASSIUM TRIS (OXALATO) FERRATE(III) TRIHYDRATE
5.1 About 5g ferrous ammonium sulphate salt is weighted. The actual weight used was recorded. It
was put into a 125 mL Erlenmeyer flask. This compound was dissolved with 15 mL of distilled
water and 5 drops of 3M sulphuric acid was added.
5.2 50 mL of oxalic acid was added to this solution and was heated until boiling. Solution was
stirred constantly to prevent bumping.
5.3 The Erlenmeyer flask was removed from the heat. Yellow precipitate of FeC2O4 was allowed
to settle. The supernatant liquid was decant and the precipitate were washed using 20 mL of hot
distilled water. The mixture was swirled and the precipitate was allowed to settle. The washing were
repeat and decant once more.
5.4 20 mL of 1M K2C2O4 was added to the precipitate. It was stirred and heat to 40℃, 10 mL of 6%
H2O2 was added immediately. It was dropwise and stirred continuously. The temperature was made
sure does not go below 40℃ and not above 50℃ during the addition of hydrogen peroxide. Some
brown precipitate of Fe(OH3) was form at this time.
5.5 The resulting solution was heated until boiling. 20 ml of 0.5M H2C2O4 was added all at once
while maintaining the temperature near boiling. The solution turned clear green. Some brown
residue remained, more 0.5M H2C2O4was added dropwise while the solution boiled, until it turned
clear green.
5.6 The solution was cloud, a clean 125 mL Erlenmeyer flask was gravity filter. Solution was
swirled constantly while 15mL of ethanol was added to the solution slowly. An ice bath was
prepared in a 400 mL beaker to allow cooling. The bottom portion of the flask was immersed in the
ice bath and the solution was slowly stirred until crystal formed. Stirring was stopped to allow the
solution to stand in the ice bath for 20 minutes. A good crop of crystal was formed before the
solution was filtered.
5.7 The vacuum filtration apparatus was prepared.
5.8 the supernatant liquid was decant away from the green crystals. The crystal was transferred to
the Buchner funnel with the aid of a clean rod and suction was applied for about 2 minutes.
5.9 The suction was stopped and 10 mL 1:1 ethanol/water solution was added. Wait for 30 seconds
and suction was applied for 2 minutes. The washing process was repeated . The suction was allowed
to continue for a further 2 minutes after the final wash.
5.10 The crystal was transferred to a preweighted labelled dry 50 mL beaker . The Wash solution
was discarded.
6.0 PROCEDURE
PART A
STANDARDISATION OF POTASSIUM PERMANGANATE SOLUTION
6.1 The burette was filled with the K MnO4 solution to be standardised
6.2 20 mL of the standard oxalic acid solution was pipette into a 250 mL conical flask and 20 mL
of 2 M H2 SO4 was added.
6.3 The conical flask warmed for about 80℃ and the permanganate solution was titrated against the
oxalic acid solution. The K MnO4 solution was added slowly or manganese IV oxide ( a brown
solid) may form instead of manganese (II) ion. The end point was reached when the addition of one
drop permanganate solution produce a permanent pink colour. The results was recorded in a table
shown below.
6.4 The titration was repeated until consistent results are obtained.
PART B
DETERMINATION OF THE PERCENTAGE LIGANDS IN K3 [Fe(C2O4 )3] ∙ 3H2O
6.5 0.20 g of the coordination compound that was previously prepared was weighted out .
6.6 The sample was boiled with 50 mL of 1M sulphuric acid in a conical flask.
6.7 The solution was allow to ccol down to 60℃ and titrated slowly with the K MnO4 solution
provided .
6.8 The endpoint reached when the addition of one drop of permanganate solution produced a
permanent pink colour. The results was recorded in the table shown below.
6.9 The titration was repeated until consistent results are obtained.
7.0 RESULT
Synthesis of potassium tris (oxalato) ferrate (III)
1.
Mass of Fe(NH4)2(SO4)2.6H2O used = 5.0246 g
2.
Moles of Fe(NH4)2(SO4)2.6H2O used = 0.0128 mol
3.
Mass of K3[Fe(C2O4)3].3H2O obtained = 4.9822 g
4.
Theoretical yield of K3[Fe(C2O4)3].3H2O (moles) = 0. 0128mol
5.
Theoretical yield of K3[Fe(C2O4)3].3H2O (mass) =6.2851g
6.
Percent yield of K3[Fe(C2O4)3].3H2O = 79.27%
A. Standardization of potassium permanganate solution
Rough
Accurate titrations
estimation
1
2
Final burette reading (mL)
19.00
18.55
38.45
Initial burette reading (mL)
0.00
0.00
20.00
Vol. of KMnO4 used (mL)
19.00
Mean vol. of KMnO4 used (mL)
18.55
18.45
18.50
B. Determination of Percentage of Ligands in K3[Fe(C2O4)3].3H2O
Rough
Accurate titrations
estimation
1
2
Mass of K3[Fe(C2O4)3].3H2O (g)
0.2012
0.2004
0.2002
Final burette reading (mL)
23.20
22.50
32.20
Initial burette reading (mL)
0.00
0.00
10.00
Vol. of KMnO4 used (mL)
Mean vol. of KMnO4 used (mL)
23.20
22.50
22.35
22.20
8.0 CALCULATION
SYNTHESIS OF POTASSIUM TRIS (OXALATO) FERRATE (III)
!
Fe(NH
4 )2(SO4) ∙ 6H2O (aq) + !H2C2O4 (aq)
!
FeC
2O4 (s) + … etc ——-> (1)
2
5.0246g Fe(NH
!
! !
4 )2(SO4) ∙ 6H2O ×
2
1 m ol
Fe(NH4)2(SO4 ) ∙ 6H2O
392.13 g /m olFe(NH4)2(SO4 ) ∙ 6H2O
= 0.0128 mol
FeC2O4 + K2C2O4 ∙ H2O+H2O2
H2O
!Fe 3+ +
HO−2 +
+
Fe(OH3) (s) + …etc
2Fe 2+ → 2Fe 3+ +
———> (2 and 3)
3OH −
3OH − → Fe(OH )3
0.0128 mol !FeC2O4 ! ×
= 0.0128 mol !Fe(OH3)
1 m ol Fe2+
×
1 m ol FeC2O4
Fe(OH3) + H2O2 + K2C2O4
0.0128 mol K3 [Fe(C2O4 )3] ∙ 3H2O ×
2
m ol
2
m ol
Fe 3+
Fe2+
×
1 m ol Fe(OH )3
1 m ol Fe 3+
K3 [Fe(C2O4 )3] ∙ 3H2O (aq) +… etc
2
m ol
2
———> (4)
K3 [Fe(C2O4 )3] ∙ 3H2O
m ol
Fe(OH )3
= 0.0128 mol K3 [Fe(C2O4 )3] ∙ 3H2O
Theoretical yield
0.0128 mol K3 [Fe(C2O4 )3] ∙ 3H2O ×
6.2851 g K3 [Fe(C2O4 )3] ∙ 3H2O
Percentage yield
4.9822g
×
6.2851
100 = 79.27%
491.21 g /m ol
1
m ol
K3 [Fe(C2O4 )3] ∙ 3H2O
Fe(C2O4 )3 ∙ 3H2O
PART A
STANDARDISATION OF POTASSIUM PERMANGANATE SOLUTION
2K MnO4 + 3H2 SO4
+
5H2C2O4 ∙ 2H2O ⟶ K2 SO4 +
1) No of moles of oxalic acid
0.05M × 0.020 L
mol= 1 × 10−3
5 mol of C2O4 : 2 mol of MnO−
4
1 × 10−3 mol : 4 × 10−4
Molarity of Potassium permanganate
M= mol/L
M=
4 × 10−4 m ol
0.01850l
M= 0.0216
2Mn SO4 + 18H2O + 10CO2
PART B
DETERMINATION OF THE PERCENTAGE LIGANDS IN K3 [Fe(C2O4 )3] ∙ 3H2O
22.50 + 22.20
=
2
22.35ml
2(MnO4− + 5e − + H + ⟶ Mn2+ +
4H2O)
5(H2C2O4 ⟶ 2CO2 + 2e − + 2H +)
2MnO−4 + 6H + + 5H2C2O4 ⟶ 2Mn2+ +
8H2O
+
10CO2
Moles of MnO−
4 = M(L)
2 moles of MnO−
4 = 5 moles ofH2C2O4
0.0216M
=
×(
4.83 × 10−4
4.83 × 10−4
20.35
ml
×
1l
)
1000ml
m ol
m ol MnO−4
×
5
m oles of H2C2O4
2 m oles of MnO−4
Mass of potassium tris (oxalato)ferrate (III) trihydrate.
1.21 × 10−3
m ol × 88.02 g/mol
= 0.1065g
0.1065g
×
0.2003
100 = 53.17%
=
1.21 × 10−3
m ol
H2C2O4
9.0 DISCUSSION
The objective of this experiment is to synthesis a coordination compound, Potassium tris
(oxalato) ferrate (III) trihydrate under carefully controlled conditions, and to standardise the
potassium permanganate solution as well as, to discover the percentage of ligands in
! 3 [Fe(C2O4 )3] ∙ 3H2O. The concept of the experiment is based on the purpose of synthesising a
K
coordination compound. The synthesising process is generally applied in many chemical
researches. Synthesis process often involves a number of chemical reactions.
Moreover, for the experiment of synthesising potassium tris (oxalato) ferrate (III), it involves in
the formation of a new compound called coordination compound. Coordination compounds can be
defined as compounds in which several ligands are coordinated to a transition metal cation. Ligands
are coordinated to a transition metal cation. A ligand is any substance (neutral or anion) which can
act as a Lewis base donating electron to the transition metal which act as a Lewis acid. Thus,
coordination complex must contain a transition metal cation and a several ligands.
The potassium tris (oxalato) ferrate (III) trihydrate, is synthesised by two processes. The first
reaction involves dissolving of ferrous ammonium sulphate in excess oxalic acid. The process result
in the isolation of the iron (II) oxalate, FeC
!
2O4, in the form of yellow precipitation.
Fe(NH4 )2(SO4) ∙ 6H2O (aq) + H2C2O4 (aq)
2
FeC2O4 (s) + H2 SO4 +(NH4 )2(SO4 ) +
6H2O
The compound is then heated to ensure dehydration of solution and isolation all of the iron as
ferrous oxalate. After all the yellow precipitates allowed settling, decantation of the supernatant is
performed. This step is essential to remove more oxalic acid and improves purity of precipitate.
In the second process potassium tris (oxalato) ferrate (III) trihydrate was formed after addition of
potassium oxalate, hydrogen peroxide and oxalic acid .
First during the heating of iron complex with potassium oxalate, continuous stirring are essential
to prepare a well mixed uniform suspension for a complete oxidation in the next step. Secondly,
during the addition of H2O2 the hot suspension to oxidise the iron in the suspended particles from
ferrous to ferric, it is a must to keep solution at 40℃ throughout handling this step. Since they are
solid tiny crystals they only react through their surface area. Stirring and several minutes cooking
time are also necessarily here. This step should completely dissolve the yellow precipitate. At some
point, a brown precipitate of Fe(OH3) remains and is reluctant to dissolve. This will affect the
yield as not all ferric iron is available to make the ferric oxalate molecular anion for the core of the
green crystals.
After addition of potassium oxalate and hydrogen peroxide has occurred, the equation involved in
H2O
Fe 3+ +
HO−2 +
+
2Fe 2+ → 2Fe 3+ +
3OH −
3OH − → Fe(OH )3
Because of the high concentration of OH − ion brown precipitate was formed. After that, more
oxalic acid was added which caused the brown precipitate to dissolve and the soluble complex was
formed. The full equation is
3K2C2O4 +
3H2C2O4 → 2K3 [Fe(C2O4 )3] ∙
2Fe(OH )3 +
3H2O
+
3H2O
After crystallization, a bright green crystal was formed. From this, the actual yield is obtained by
weighting. The theoretical yield is calculated by using the number of moles of product from the
limiting reactant, which is 6.2851g. The percentage yield obtained with the formula of
Act u al yiel d
T h eoret ical yiel d
×
100 which is equal to 79.27%
Next for, the experiment of determination of percentage ligands K3 [Fe(C2O4 )3] ∙ 3H2O. In order
to find the percentage , titration method that involves redox titration process must first be
conducted, to identify the amount of oxalate ligands that are attached to each of the metal centers.
For this experiment, potassium permanganate solution is used as the titrant.
In the first part of the experiment, the standardisation of potassium permanganate solution takes
place. For the titration, the standard solution is oxalic acid. Oxalic acid is suitable to be used
because it is available in solid form so it is not hygroscopic. The titration was stopped once a
permanent pink colour was produced. This indicates that the procedure already reached the end
2+
point as there was no more oxalic acid able to reduce MnO−
4 ion to Mn . The overall reaction
involved is as below :
2MnO−4 + 6H + + 5H2C2O4 ⟶ 2Mn2+ +
8H2O
+
10CO2
Because the molarity and volume of oxalic acid has already been calculated, therefore, the amount
of oxalic acid that reacted with potassium permanganate solution can be identified. For the equation
above, the molarity of potassium permanganate is 0.0216 M
In part B, the determination of the percentage ligands in K3 [Fe(C2O4 )3] ∙ 3H2O takes place. The
coordination compound that was prepared earlier was titrated with a standardised potassium
permanganate solution until it produced a permanent pink colour to show the end point had already
reached. The percentage by weight of ligands in K3 [Fe(C2O4 )3] ∙ 3H2O was 53.17%
Some errors might occur during handling these experiments. During transferring compounds from,
some of it left in the weighting boat, leading to inaccuracy of the compound mass. The compound
was not completely dissolved in the solvent before mixing with other solution because of improper
stirring condition. There was also an error while transferring the mixture into the Buchner funnel
during suction filtration. The mixture was not poured carefully onto the very center of filter paper
which may cause the sample to be under the edges of filter paper.
During conducting the experiment, there are several safety precautions needed such as, while
handling the hot glassware, use tongs to hold and white tile to place the flassware after heating.
Next, do not use thermometer to stir the solution. furthermore, pour acid into water, not water into
acid and wear gloves as some chemicals such as concentrated acid is corrosive to skin. The eyes
must also be perpendicular to the scale to avoid parallax error.
In order to improve accuracy, there are several suggestions such as , during transferring the
compound from the weighing boat. Rinsing can be done to ensure the entire compound is
successfully transferred. Instead of using the glass rod stir, we can also use the magnetic stirrer to
ensure that all salts are completely dissolved in the solvent.
10.0 CONCLUSION
The objective is achieved and that is, synthesis a coordination compound, potassium tris (oxalato)
ferrate(III) Trihydrate under carefully controlled conditions. Hence, Potassium tris (oxalato) Ferrate
(III) Trihydrate, was K
! 3 [Fe(C2O4 )3] ∙ 3H2O synthesized. The actual mass obtained 4.9822g while
the theoretical yield obtained 6.2851g. Therefore, the percentange yield is 70.13% . Next, the
objectives of the experiment to standardised the potassium permanganate solution and to discover
the percentage ligands in !K3 [Fe(C2O4 )3] ∙ 3H2O was achieved. The amount of molarity of the
Potassium permangante is 0.0216M. Thus, based on the result that has been obtained, the
percentage of the ligands in !K3 [Fe(C2O4 )3] ∙ 3H2O is found to be 53.17%.
11.0 QUESTIONS
PART A
1) From the average volume of K MnO4 solution used, calculate the concentration of the solution.
- 0.0216M
2) Why is it necessary to heat the oxalic acid solution?
- The oxalic acid is heated before the titration with K MnO4 is because the reaction happens at
certain temperature only. If the oxalic acid is not heated, the permanent pink color at the endpoint
will turn brown soon and the reaction will take a longer time.
3) In this experiment oxalic acid is used as a reducing agent, could oxalic acid be used as a primary
standard to standardise a solution of a base such as sodium hydroxide? Explain your answer.
- yes oxalic acid can be used as the primary standard to standardise a solution of a base. This is
because it can be precisely weighed out in pure form so that the number of moles present can be
accurately determined from the measured weight and the known molar mass.
PART B
2+
1) Given that MnO−
ion, and C2O42− ion is being oxidized to CO2, write
4 is being reduced to Mn
a balanced redox equation for the above titration. Use the equation to calculate the
concentration of the oxalate ions in the coordination compound.
- MnO−4 + 16H + + 5C2O4 ⟶ 2Mn2+ + 8H2O
- Concentration : 0.63 M
+
10CO2
2) Calculate the percentage by weight of oxalate ions in the complex. Compare this with the
theoretical value and thus obtain the percentage purity of the complex.
Moles of MnO−
4 = M(L)
2 moles of MnO−
4 = 5 moles ofH2C2O4
0.0216M
=
×(
4.83 × 10−4
4.83 × 10−4
20.35
ml
×
1l
)
1000ml
m ol
m ol MnO−4
×
5
m oles of H2C2O4
2 m oles of MnO−4
Mass of potassium tris (oxalato)ferrate (III) trihydrate.
1.21 × 10−3
m ol × 88.02 g/mol
= 0.1065g
0.1065g
×
0.2003
100 = 53.17%
=
1.21 × 10−3
m ol
H2C2O4
12.0 REFERENCES
1.
N., P. (2013). Determine concentration of KMnO4 solution. Retrieved May 29, 2020, from
https://amrita.olabs.edu.in/?sub=73
2.
Harvey, D. (2016, July 21). Complexation Titration. Retrieved May 29, 2020, from https://
chem.libretexts.org/Bookshelves/Ancillary_Materials/Demos,_Techniques,_and_E
xperiments/General_Lab_Techniques/Titration/Complexation_Titration
3.
Bae, J. (2018, April 11). How do you calculate the percentage of ligands bound to receptors
given specific kDa and concentration? Retrieved May 29, 2020, from https://
www.researchgate.net/post/How_do_you_calculate_the_percentage_of_ligands_b
ound_to_receptors_given_specific_kda_and_concentration
EXPERIMENT 1
Predicting Molecular Shape and Polarity Using VSEPR Theory