THE Preparation, Photochemistry AND Analysis OF Potassium Ferrioxalate PDF

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Analysis of Potassium Ferrioxalate experimental...

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InorgChem Experiment No. 2 THE PREPARATION, PHOTOCHEMISTRY AND ANALYSIS OF POTASSIUM FERRIOXALATE (POTASSIUM TRIOXALATO-FERRATE(III)) Aims 

To prepare Potassium Ferrioxalate.



To examine the product using Infra-red spectroscopy.



To explore and gather a deeper knowledge about Iron complexes and their formation.



To explore the technique of recrystallization, as a method of purification.

Introduction Iron is a metal within the transition metal series. Transition metals are described as metals within the d block of the periodic table, of whom have partially filled d levels which can give rise to cations that have partially filled d levels. There are many characteristics of the transition metals that are not found in other compounds. They can form many compounds with different oxidation states and this is due to the fact that there is a relatively low energy gap between the different possible oxidation states. (2) In addition transition metals can form many paramagnetic compounds due to the unpaired d electrons, these two characteristics can be seen in the product of this experiment, Potassium Ferrioxalate. In addition, a wide range of colours can be observed in transition metal complexes and this is due to charge transfers. Charge transfer transitions are when electrons jump from a ligand orbital to a metal orbital charge, this gives rise to a ligand to metal transfer. D-d transfers can also occur and this is when an electron jumps from one d-orbital to another d-orbital. The different colours can be observed when this occurs, as not all d-orbitals have the same energy in the transition metals. Charge transfers result in much deeper colours than d-d transitions do.

Pre-practical questions

1. Oxalate dianion

2.

.

Three bidentate oxalate ions bind to the iron centre and their geometrical configuration around the iron atom is octahedral.

3. The electronic configuration of iron in this atom is [Ar] 3d6, 4s2. I predict it has 4

unpaired electrons, because in the diagram it has four unpaired electrons. Crystal field

splitting diagram for Iron complex:

4.

This configuration is often associated with colourless compounds due to the fact the distance between the electrons in the eg level and t2g level. This distance dictates the energy that the complex will absorb from white light, meaning that not a lot of energy from white light will be absorbed and therefore this configuration is normally associated with colourless compounds.

Experimental Procedure A. Preparation FeCl3.6H2O (5.3 g; 0.0278 moles) was dissolved in deionized water (8 cm3). Hence, K2C2O4.H2O (12 g; 0.0654 moles) was dissolved in a beaker with water (20 cm3), the solution was placed on a hot plate (at 50◦C) with a magnetic stirrer. The iron solution was added to the beaker. The yellow- brown colour of FeCl 3 was replaced by the deep- green colour of the complex. The solution was cooled in an ice bath until Crystals formed. The liquid that remained in the beaker was then decanted and the solid crystals were dissolved in warm water (20 cm3). The solution was allowed to crystallize again by cooling in the ice-bath. The final product was filtered using Buchner filtration. The Crystals were washed using a mixture of equal volumes of water and ethanol (10 cm3). The Crystals were then just washed with ethanol (8 cm3). The Crystals were then placed on a preweighed boat and the weight of the Crystals was calculated to be 6.79 g. The percentage yield of Potassium ferrioxalate was calculated to be 61%. B. Tests on the Product

1. In a fume hood a small sample of the Crystals were taken and placed in a porcelain crucible. Upon ignition and heating the product went from Green  Yellow  Brown. 2. A Blueprint experiment was carried out by the demonstrator. The procedure for what was observed is as follows: A key was selected as the object to photograph. Ferrioxalate (0.2 g) was taken and dissolved in the minimum amount of water. The filter paper was dampened with the solution. The object was placed on the filter paper and it was exposed under UV light for two minutes. The light source was hence removed and the paper was sprayed with a solution of potassium hexacyanoferrate (III) using a tweezers. It was observed that the area surrounding the key went a Prussian blue colour, but underneath the key the colour did not change. C. Determination of Oxalate (Chemical Analysis) Using an analytical balance, Ferrioxalate salt from A (0.2046 g) was weighed out and then dissolved in dilute sulfuric acid (20 cm3) in a conical flask (250 cm3). The solution was heated nearly to boiling on a hot plate and hence the solution was titrated with Potassium permanganate (0.02M), until the liquid went very pale pink. The percentage weight of oxalate in the compound was calculated to be -------------. Results Results sheet Name: Aloisia King/ Etaoine McDermott-partner

POTASSIUM FERRIOXALATE

Wt. boat + crystals

= 9.19g/mol

Wt. boat

= 2.70g/mol

Wt. crystals

=

6.49g/mol

"

=

0.2046g/mol

"

(total) ( after removal for tests)

Moles FeCl3.6H2O

= 0.0278 moles

Moles K2C2O4.H2O

= 0.0654 moles

Theoretical yield, moles

= 0.0312/ 0.0218 x 100 = 60.55 approx equal to 61%

Mr of FeCl3.6H2O= 55.847 + 3(35.453) + 6(2(1.0079) + 15.9994) = 190g/ mol Mr of K2C2O4.H2O = 2(39.0983) + 2(12.011) + 4(15.9994) + 2(1.0079) + 15.9994 = 184g/ mol Mr of Potassium Feroxalate = 3(39.0983) + 55.8473 + 3((2(12.011) + 4(15.9994)) + 3(2(1.0079+15.9994)) = 491.25 g/mol

Test 1 observations upon heating the crystals went from Green  Yellow  Brown.

Test 3 observations and 'blueprint' everything surrounding the key went Prussian blue, but underneath the key didn’t change colour it stayed the colour of the filter paper.

POTASSIUM FERRIOXALATE

(2)

Oxalate analysis

Wt. sample

= 0.2024g

Burette readings, using permanganate of molarity:__0.02________M

After (first)

= 0 cm3

Before

= 0 cm3

Titre (first)

= 29.2 cm3

29.2/1000

= 0.0292L 0.0292x0.02= 0.000584 moles of permanganate.

For every potassium permanganate there was 2.5 of oxalate 0.000584 x 2.5 = 0.00146 moles of oxalate. Mr of oxalate= 2(12.011) + 4(15.9994) = 88.0196. 0.00146 x 88.0198 = 0.1285g of oxalate in solution. 0.1285/0.2046 x 100 = 62.80% approx 63% is the percentage of oxalate in the product. 3(88.0196)/ 491.25 x 100 = 53.75 approx 54% yield for all the oxalate.

Post-practical questions: 1) Haemoglobin and myoglobin are two biologically significant compounds containing complexed iron. 2) Cyanide is more poisonous because it binds irreversibly to the iron within haemoglobin of the red blood cells, which ultimately prevents the transportation of oxygen within the body. In ferricyanide the cyanide ligands are already bonded strongly to an iron atom, therefore they cannot move as freely. This means they are not as able to bond to haemoglobin if they enter the bloodstream. This means potassium ferricyanide is much less poisonous than potassium cyanide. Swallowing large amounts of iron oxide is a possible antidote for cyanide poisoning as 3) Colorimetric analysis is based on the change in the intensity of the color of a solution with the variations in concentration. Infrared spectroscopy was used as the method of colorimetric analysis in this experiment, it is a characterization tool that is used to help determine the molecular structure. IR is based on the fact that functional groups absorb specific frequencies of energy based on their structures. (1) The molar extinction coefficient was calculated to be 1170.21 mol-1cm-1 using the formula : E=A/Cl 1.10=A obtained from spectrum C= 0.00094 mol/L-1 L= 1cm E=1.10/0.00094 (1) 1170.21/1000= 1.17 if knew E and was plugging into eqn. 0.94 mM was given but it was converted to moles per litre, so could use the beer lambert equation by multiplying by 10-3 .

References: 1) www.chegg.com 2) Matsumoto, Paul S (2005). "Trends in Ionization Energy of TransitionMetal Elements". Journal of Chemical Education. 82 (11)...