Experiment 4: Preparation of Potassium Tri(oxalate)aluminate(III)trihydrate
Objective
1. Synthesis potassium tri(oxalate)aluminate(III) trihydrate
Reagents
Apparatus
Potassium Hydroxide (KOH)
Beaker (250 Ml)
Oxalic Acid Dehydrate (H2C2O4. 2H2O)
Graduated Cylinder
Ethanol
Hot Plate
Acetone
Glass Rod
Distilled Water
Buchner Funnel Filter Paper Watch Glass Aluminium Foil
Introduction
Aluminium, like many of the transition metals, forms octahedral complex ions. In this lab we will synthesize potassium tris(oxalato)aluminate(II tris(oxalato)aluminate(III), I), K 3[Al(C2O4)3]•3H2O.
First, let’s cover some background on aluminium. Like several other metals, aluminium is reactive enough to displace hydrogen from water. However, this does not take place because aluminium develops a layer of aluminium oxide that protects the metal surface. This oxide coating can be dissolved by acid, according to the equation shown below. -
3+
Al2O3 + 3HCl → 6Cl + 2Al + 3H2O
But, in this experiment the oxide coating is dissolved by excess hydroxide, forming the -
[Al(OH)4] ion. The chemical equation for this particular reaction is as follows: -
Al2O3 + 2OH + 3H2O → 2[Al(OH)4]
-
Procedure
1. Aluminium foil was cut into roughly one-centimetre squares and measure approximately 0.50 grams (this should require 12-14 squares of foil). The exact mass used was recorded.
2. The foil was transferred to a 250-mL beaker.
3. Using a graduated cylinder, 30 mL of water and 15 mL of 4.0 M KOH was added. A stirring rod was used to ensure that the aluminium foil is submerged.
4. When the reaction has subsided, the solution was heated to boiling on a hotplate to dissolve any unreacted aluminium.
5. Next, 8.0 grams of oxalic acid dihydrate was added, in small portions, to the hot solution.
6. The hot solution was filtered through a Buchner funnel and the filtrate was transferred back to the 250-ml beaker.
7. The beaker was placed in an ice bath and was cooled to 10 C.
8. 20 mL of ethanol was added approximately and the beaker was leave in the ice bath until crystallization appears complete.
9. The product was recovered by suction filtration, rinsed with 10mL of acetone, and was allowed to dry.
10. The sample was weighted and recorded.
Result
Discussion
In this experiment, K 3[Al(C2O4)3]•3H2O was synthesized. First, aluminium metal is -
reacted with potassium hydroxide to produce the [Al(OH)4] ion. Next, oxalic acid (H2C2O4) is added, which neutralizes the excess hydroxide and provides a source of the oxalate ion. Lastly, 3-
the [Al(C2O4)] ion that is produced is precipitated as the potassium salt by the addition of ethanol. Ethanol is added to reduce the polarity of the solution. The overall reaction is represented by the equation shown below.
Al + 3KOH + 3H2C2O4•2H2O → K 3[Al(C2O4)3]•3H2O + 6H2O + 3/2 H2
From the calculation the limiting reagent are both aluminium and potassium hydroxide. The theoritical
value
that
calculated
should
yield
about
7.4
gram
of
potassium
tri(oxalate)aluminate(III) trihydrate. From the experiment we managed to synthesized 5.389 gram of potassium tri(oxalate)aluminate(III) trihydrate. From the formula :
Conclusion
We have successfully synthesized our desired product Potassium Tri(oxalate)aluminate(III)trihydrate with a yield of 73%.
References
House, J. E. (2013). Inorganic Chemistry 2nd Edition. Oxford: Elsevier. McClure, M. (2009). Retrieved December 2, 2014, from University of North Carolina at Pembroke web site: http://www2.uncp.edu/home/mcclurem/courses/chm226/introduction_Coordination Silberberg, M. S. (2013). Chemistry: The Molecular Nature of Matter and Cha nge 6th edition. New York: McGraw-Hill.
