PREPARATION OF POTASSIUM TRIS(OXALATO)FERRATE(III) TRIHYDRATE K3[Fe(ox)3].3H2O
To synthesise the potassium tris(oxalate)ferrate(III) trihydrate complex using ferric sulphate in the presence of excess oxalate ions present in both the reactants barium oxalate and potassium oxalate monohydrate.
II. INTRODUCTION The synthesis of the potassium tris(oxalate)ferrate(III) trihydrate complex was first noted in 1939 by Blair and Jones.1
The reaction featured below is the focus of the experiment, yielding the product of interest, potassium tris(oxalate)ferrate(III) trihydrate.
Fe2(SO4)3 (s) + 3 Ba(ox)(s) + 3K2(ox).H2O(s) 2K3[Fe(ox)3].3H2O(aq) + 3BaSO4 (s)
Potassium tris(oxalate)ferrate(III) trihydrate is a octahedral complex with three oxalate ligands coordinating to the hard metal centre, Iron. The iron is coordinated to a hard base as oxygen acts as the electron donor, promoting the stability of the complex. The stability of this complex is heightened by the fact that oxalate is a bidentate ligand, that is, each oxalate as two binding sites available.
The following chemicals were weighed out; 5.0195 grams of Ba(ox), 2.762 grams of K2(ox).H2O and 2.5417 grams of Fe2(SO4)3 using an electronic mass balance appropriately. All the chemicals were dissolved in 60 cm3 of deionised water using a clean dry beaker of appropriate size. The mixture was heated on the steam bath for an hour whilst stirring consistently. The two people making up the group took turns with the stirring aspect of the procedure. 10 cm3 of deionised water was added at when required to counteract the evaporation of water. After the mixture was heated for one hour, it was filtered twice through suction. The filtrate was then collected in a sample beaker was labelled and left in a dark cupboard for a week. A week later the solution was taken out of the cupboard. The crystal that was anticipated to form had not formed. To obtain a yield sufficient acetone was added to the solution to stir. It was left for a few minutes to allow crystals to develop and then filtered by suction. The residue was then weighed. Three samples of 0.2 grams were weighed out into 3 dry conical flasks to act as individual analytes. These samples were each dissolved in 10 cm3 of H2SO4 and then heated to 80 using a hot plate before it was titrated with 0.0218M of KMnO4.
Steps taken to calculate the moles and mass of K3(Fe(ox)3).3H2O n[Ba(ox)]
5.0195/225.32= 0.022278mol for ratio purposes: 0.0190686mol n[K2(ox).H2O]
for ratio purposes: 0.0190686mol n[Fe2(SO4)3] 2.5417/399.88= 0.0063562mol for ratio purposes: 0.0063562mol n[K3(Fe(ox)3).3H2O] n[K3(Fe(ox)3).3H2O]: n[K2(ox).H2O]= 1:3 n[K3(Fe(ox)3).3H2O]= (2/3)x 0.01410mol
= 0.0094mol m(K3(Fe(ox)3).3H2O) 0.0094x491.258= 6.245g (theoretical)
ACTUAL MASS WEIGHED: 4.6178g
Percentage yield = (4.6178/6.245) x 100%= 73.94%
Titration calculations from Part B
5C2O4- + 2MnO4- + 16H+ => 10 CO2 + 2Mn+2 +8H2O
Titre (c= 0.0218) n(KMnO4) n(ox) Sample 1: mass of K3(Fe(ox)3).3H2O= 0.2045g v(KMnO4)= 0.0237L
Sample 2: mass of K3(Fe(ox)3).3H2O= 0.2056g v(KMnO4)= 0.0240L
Sample 3: mass of K3(Fe(ox)3).3H2O= 0.2044g v(KMnO4)= 0.0236L (best result based on visual observation)
IR spectrum of K3(Fe(ox)3).3H2O
Obtained peak (cm-1)
Expected peak (cm-1)
1720-1700 C=O group (bond shifted)
1320-1200 C-O (bond is shifted)
V. SAFETY AND PRECAUTIONS
Comment and precautions
Harmful if swallowed, may cause serious eye irritation, may cause respiratory irritation.
Avoid breathing dust/fume therefore perform experiment in the fume cupboard. Wash skin thoroughly if skin is exposed to the chemical. Avoid exposure by wearing gloves.
Barium chloride dihydrate
Toxic if swallowed, harmful if inhaled, may cause skin