Download Preparation of Potassium tris oxalate fe

Chim367:Inorganic Lab
Exp.3: Preparation of Potassium
tris(oxalate) ferrate(III)
trihydrate. K3[Fe(C2O4)3].3H2O
Name: Doha Faraj
File No. : 77022
Group (7)
1
o Abstract:
▪
▪
▪
In this experiment, The Fe3+ complex K3 [Fe (C2O4)3].3H2O was prepared. This was achieved by
first making a Fe2+ complex (ferrous oxalate - FeC2O4) and then adding potassium ion.
Followed by oxidation of Fe2+ to Fe3+ using hydrogen peroxide.
The crystals obtained are green in color.
o Introduction:
▪
Potassium tris(oxalato)ferrate (III) is an iron metal complex having three oxalate ligands(C2O42bonded to the central metal atom. The ligand is a bidentate, meaning that it binds to the metal
atom at 2 different places.
▪
The metal complex has the chemical formula K3[Fe(C2O4)3].3H2O.
▪
This compound is a photosensitive material ( changes upon exposure to light ) and therefore it is
commonly used as acidometer to determine monochromatic radiant fluxes from the ultraviolet to
visible wavelengths, and it's also used in Platinum/Palladium photographic printing.
▪
The resulting geometry is an octahedral structure, which can be considered as distorted
octahedral due to strict effect due to the bending of the ligand, the different ways the ligands
attach causes the appearance of a stereoisomers.
▪
In this experiment the complex was synthesized via oxalic acid which was added to ferrous
ammonium sulfatehexahydrate (Fe (NH4)2(SO4)2·6H2O) under acidic conditions.
▪
This forms iron (II) oxalate (FeC2O4), a yellow precipitate.
▪
This is then added to potassium oxalate (K2C2O4) followed by hydrogen peroxide to oxidize the
Fe from a (II+) to (III+) state, which will finally synthesize the desired product that is green in
color.
2
▪
An alternative procedure exists which involves adding potassium oxalate directly to Iron (III)
chloride hexahydrate which gives the desired product, in the method we used there are more
steps, more intermediates and more reactants required, in addition to the fact that some of the
reactants used are also rather dangerous and harmful, such as hydrogen peroxide.It is therefore
the less favored method out of the two.
▪
In the second part after the complex has been prepared it was subjected to analysis to determine
the percentage of oxalate in the sample.
▪
This was done by decomposing the complex to its ions by adding hot acid and then titrating the
oxalate ions with MnO4- ( Ox-Red reaction). The obtained values were then compared with the
theoretical percentage of oxalate ions.
▪
It must be further noted that extra precaution must be held during analysis of the the complex
sample due to its photosensitivity.
o Reactions:
▪ The experiment involves two parts. The first part is the formation of the yellow precipitate [iron
(II) oxalate (FeC2O4)] according to the following reaction:
Fe (NH4)2(SO4)2.6H2O + H2C2O4  FeC2O4 + 6H2O + H2SO4 + (NH4)2SO4
▪ The second part is the formation of the complex and composed of 2 reactions:
3 H2O2 + 6 FeC2O4 + 6K2C2O4   4K3 [Fe (C2O4)3].3H2O + 2Fe (OH) 3
▪ The second reaction is the reaction of formation of the complex.
K2C2O4.H2O + Fe (OH) 3 + 3 H2C2O4  2K3 [Fe (C2O4)3].3H2O
▪ The side reactions that might occur:
- The photosynthetic decomposition of the complex:
2[Fe (C2O4)3]3+ + h𝞾  2[Fe (C2O4)2]2+ + C2O42- + CO2
- The thermal decomposition of hydrogen peroxide:
2 H2O2  2 H2O + O2
3
o Discussion & Procedure:
Name
Formula
Ferrous
ammonium
sulfate
hexahydrate
Sulfric acid
Oxalic acid
Sulferic acid
Hydrogen
peroxide
Fe(NH4)2(SO4)2.6H2O
H2SO4
H2C2O4.2H2O
H2SO4
H2O2
Molar
mass
(g/mol)
392
98
126
98
34
BP
MP
--
280
-337
108
Quantity
used(mlg)
100-110
5g
-35
101.5
10
-33
1ml
10g
1.84
9ml
o Observation:
 Upon the addition of oxalic acid, the color becomes yellow due to the
precipitate Fe2C2O4.
4
 Upon the addition of Potassium oxalate, a brown color is observed. Fe
(OH) 2 precipitate.
 Upon the addition of Hydrogen peroxide H2O2, a black color is observed.
 Hydrogen peroxide with its oxidative role causes the transformation of Fe (II) to Fe
(III) and during this process a black color is observed.
Finally
the green color upon the addition of H2C2O4 that leads to the dissolving of all brown
colored Fe(OH) 3 precipitate ,where it continues with the formation of
K3 [Fe (C2O4)3].3H2O. Clearly the green color is the color of our component.
o Calculation:
All Fe ions that were present in the starting material Fe (NH4)2(SO4)2.6H2O have been
transformed K3 [Fe (C2O4)3].3H2O, moreover the total number of moles of iron in starting material
is equal to that of the product.
So:
𝑛𝑢𝑚𝑏𝑒𝑟 𝑜𝑓 𝑚𝑜𝑙𝑒𝑠 𝑜𝑓 Fe (NH4)2(SO4)2.6H2O
1
𝑜𝑏𝑎𝑡𝑎𝑖𝑛𝑒𝑑
= 𝑛𝑢𝑚𝑏𝑒𝑟 𝑜𝑓 𝑚𝑜𝑙𝑒𝑠 𝑡ℎ𝑒𝑜𝑟𝑎𝑡𝑖𝑐𝑎𝑙𝑙𝑦
1
5
The moles theoretical of is K3 [Fe (C2O4)3].3H2O= 0.0128g
Thus the Mtheoretical = 0.0128×491.24 = 6.287g
Mexperimentally =
The % yield =
𝑀𝑒𝑥𝑝
𝑀𝑡ℎ𝑒𝑜
× 100
=
6