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MAKERERE UNIVERSITY COLLEGE OF NATURAL SCIENCES DEPARTMENT OF CHEMISTRY TRANSITION ELEMENTS PRACTICAL EXPERIMENT ONE
NAME: KWIHANGANE ANNE STUDENT NO.: 212026318 REG NO.:12/X/25708/Ps GROUP NO.: 10 INSTRUCTOR: MR. MULINDA STEPHEN COURSE CODE: CHM 2220/PS DATE OF SUBMISSION: 18TH MARCH, 2014
©Kwihangane Anne
12/X/25708/Ps
Page 1
TITLE: SYNTHESIS OF POTASSIUM TRIOXALATOALUMINATE(III), K3[Al(C2O4)3] Aim: To illustrate the complex formation of a non transition element ABSTRACT Potassium trioxalatoaluminate (III) was prepared by boiling aluminium hydroxide precipitate with an aqueous solution of oxalic acid dehydrate and potassium oxalate. The percentage of oxalate ligand in the product was determined by titrating the prepared product solutions against standard 0.002M potassium tetraoxomanganate solution. Solutions were prepared as follows; 0.002M potassium tetraoxomanganate solution prepared by measuring 25cm3 of 0.02M potassium tetraoxomanganate solution stock into a 250ml volumetric flask followed by 25cm3 of 2M sulphuric acid and the volume made up to the mark with distilled water, 1% potassium trioxalatoaluminate (III) solution prepared by measuring 0.5g of the product stock into 50ml of distilled water in a volumetric flask. No indicator was necessary since in this case, the intense purple color of the permanganate ion serves as a built-in indicator. The percentage yield of potassium trioxalatoaluminate (III) as well as the percentage of oxalate ligand in the product was calculated using stoichiometry. The percentage yield of the 1.103g of product was found to be 64.3%.The percentages of oxalate ligand were found to be 40.18, 39.72, 39.49 and 39.03 in the product. Actual mean composition of oxalate ligand by percentage was found to be 73.5 ± 0.4787%with variance of 0.2292 for the product. Theory Potassium trioxalatoaluminate (iii) is a metal complex formed between aluminium and oxalate ions both bonded to potassium as the central metal ion. According to J.D.Lee, a complex is formed when transition elements have an un parallel tendency to form co-ordination compounds with groups which are able to donate an electron pair. These groups are called ligands. The most important octahedral complex are formed with chelating ligands for example the reaction between aluminium and oxalate ions gives a complex [Al(C2O4)3]. 2Al(s) + 3C2O42-(aq)
2[Al(C2O4)3]3-(aq)
In the synthesis of potassium trioxalatoaluminate, aluminium is reacted with potassium hydroxide to form a complex and later oxalic acid is introduced to provide the oxalate ions in the solution and also neutralizes the potassium hydroxide in solution. Al(s) + 3KOH(aq) +H2C2O4 •3H2O(aq)
K3[Al(C2O4)3]•3H2O(aq) + 6H2O(l) + H2(g)
We are required to determine the concentration of the oxalate ions in solution, this will involve the introduction of potassium permanganate as the reducing agent through titration with oxalate ions in solution. The oxalate ion reduces the permanganate ions (MnO4ˉ) to Mn2+ which is nearly a colourless solution and the oxalate ions are oxidized to carbon dioxide. This is called a redox reaction where both ©Kwihangane Anne
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reduction and oxidation take place. Reduction is the addition of electrons while oxidation is the removal of electrons. No indicator is required during titration because the purple colour of the permanganate serves as a built in indicator. 16H+(aq)+ 5C2O42-(aq)+ 2MnO4-(aq)
10CO2(g)+ 2Mn2+(aq)+ 8H2O(l)
In this practical we are provided with aluminium sulphate hexahydrate and first reacted with sodium hydroxide to form a precipitate according to the equation; Al2(SO4).16H2O(aq) + 6NaOH(aq)
2Al(OH)3(s) + 3Na2SO4(aq) + 16H2O(l)
Oxalic acid is introduced in the solutions to provide an acid medium and potassium oxalate is also added to provide the oxalate ions and also provide the potassium ions that are required to form the complex which is potassium trioxalatoaluminate (iii); 2Al(OH)3(s) + 3H2C2O4.2H2O(aq) + 3K2C2O4(aq)
2K3[Al(C2O4)3](aq) + 12H2O(l)
Procedure Aluminium sulphate hexahydrate (3.5g) were dissolved in water (25cm3) and to this solution, a solution of sodium hydroxide (1.5g in10cm3 of water) was added while stirring to produce an hydroxo complex. The freshly precipitated alumimium hydroxide was filtered off and washed with (3×20cm3) of water. This precipitate was boiled with aqueous solution of oxalic acid dehydrate (2.5g) and potassium oxalate which was first prepared by dissolving them in water (50cm3) to introduce oxalate ions in the solution. Any un-reacted aluminium hydroxide was filtered off and then the filtrate was evaporated to a volume that could affect crystallization. The potassium trioxalatoaluminate (iii) was filtered off, washed with cold water and then dried in the oven at 70oC. The potassium trioxalatoaluminate(iii) was weighed after cooling in the disiccator and this mass was used to calculate the percentage yield, the sample was submitted in for inspection. To investigate the effect of sodium hydroxide on the small volumes of the potassium trioxalatoaluminate (iii), a small volume was put in the test tube and sodium hydroxide (2M) solution was added and the effect was noted. The procedure was repeated for sodium hydroxide (4M), sodium ethanoate (2M), sodium carbonate (2M). The experiment was performed on aluminium sulphate solution using the same concentration of the reagents to compare the results with that of the potassium trioxalatoaluminate(iii). Potassium trioxalatoaluminate (iii) (1g) was put in a small volumetric flask (100ml) and dissolved in water up to the mark. The solution of the product (10ml) were measured and placed in a conical flask. The potassium permanganate in the burette was ran into the flask until the colour of the solution in the flask changed to pink. The volume of potassium permanganate used was measured and noted. The procedures were repeated for replicated values of potassium permanganate and were recorded in the table. The results obtained were used to calculate the percentage yield of the oxalate ion present in the solution. ©Kwihangane Anne
12/X/25708/Ps
Page 3
When preparing potassium permanganate wear gloves because it is a strong oxidant and it stains both skin and clothes also sulphuric acid should be handled with care because it is corrosive and damages the skin when ed. One end of a capillary tube was sealed and a small amount of the product was inserted through the open end and later the tube was tied on the thermometer. The later was inserted in the beaker containing liquid paraffin. The whole set up was placed on the heat source while stirring to determine the melting point of the potassium trioxalatoaluminate. The temperature at which the first portion of the sample melted was recorded and the temperature when the whole sample melted was recorded. The melting point of the potassium trioxalatoaluminate was determined.
©Kwihangane Anne
12/X/25708/Ps
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Results Mass of samples used Mass (g)
Mass of container (g) Mass of container + sample (g) Mass of sample used (g)
Aluminium sulphate hexacahydrate 1.994
Sodium hydroxide
Oxalic acid
Potassium oxalate
1.995
1.995
1.994
5.484
3.495
4.477
5.493
3.490
1.500
2.482
3.499
Weight of the product Mass of container (g) Mass of container + product (g) Mass of product only (g)
1.995 4.245 2.250
Effect of the reagents on the product Reagent Sodium hydroxide (2M) Sodium hydroxide (4M) Sodium ethanoate Sodium carbonate Sodium orthophosphate
Observation No observable change No observable change No observable change No observable change No observable change
Effect of the reagents on simple aluminium sulphate Reagent Sodium hydroxide(2M) Sodium hydroxide (4M) Sodium ethanoate(2M) Sodium carbonate(4M) Sodium orthophosphate
©Kwihangane Anne
Observation White precipitate was formed soluble in excess White precipitate was formed soluble in excess No observable change White precipitate was formed soluble in excess White precipitate insoluble in excess
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Melting point of the product Initial temperature = 287˚C Final temperature =289˚C Melting point = = = 288˚C
Treatment of results Percentage yield = = = 64.3% 1000ml of solution contain 0.02 moles of MnO42- ions 16.80ml of solution contain
16.80 moles of MnO42- ions
=0.000336moles of MnO42- ions 2MnO42-(aq) + 5C2O42-(aq) + 16H+(aq)
10CO2(aq) + 2Mn2+(aq) + 8H2O(l)
2moles of MnO42- ions react with 5 moles of C2O4 ions 0.000336 moles of MnO42- ions react with
0.000336 moles of C2O42- ions
= 0.00084moles of C2O42- ions RFM of C2O42- = (12 2) + (4 16) = 88 Mass of the oxalate ions = Number of moles = 0.00084
RRM
88
0.0739g % of oxalate ions =
100% 100%
©Kwihangane Anne
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= 73.9%
Discussion During re-crystallization of the product Ethanol would be used because it eliminates the impurities that might otherwise escape with the final product. So the impurities in this compound may have raised the melting point of the product thus resulting into a higher value. The thread to use when tying the thermometer with the capillary tube should be strong in order to overcome the high temperature of the liquid paraffin, probably the sisal thread can be recommended.
Conclusion The experiment was successful as the complex was prepared and its melting point found without difficulty. Potassium trioxalatoaluminate (III) is a metal complex of aluminium and three ligands, all bonded to a central cation (potassium ion). Each of the three ligands binds to the metal atomt different places thus, bidentate ligands.
The melting point of potassium trioxalatoaluminate(III) was determined as 302.5oC which is in the range of the theoretical value of its melting point.
Reference J.D.Lee (1991) Concise Inorganic Chemistry, 4thedition Chapman and Hall Pg (170, 657) G. and H. Sutcliffe (1974) Practical Inorganic Chemistry, 2nd edition, Chapman and Hall.Pg (10-11) ©Kwihangane Anne
12/X/25708/Ps
Page 7
NAME: KWIHANGANE ANNE STUDENT NO.: 212026318 REG NO.:12/X/25708/Ps GROUP NO.: 10 INSTRUCTOR: MR. MULINDA STEPHEN COURSE CODE: CHM 2220/PS DATE OF SUBMISSION: 18TH MARCH, 2014
©Kwihangane Anne
12/X/25708/Ps
Page 1
TITLE: SYNTHESIS OF POTASSIUM TRIOXALATOALUMINATE(III), K3[Al(C2O4)3] Aim: To illustrate the complex formation of a non transition element ABSTRACT Potassium trioxalatoaluminate (III) was prepared by boiling aluminium hydroxide precipitate with an aqueous solution of oxalic acid dehydrate and potassium oxalate. The percentage of oxalate ligand in the product was determined by titrating the prepared product solutions against standard 0.002M potassium tetraoxomanganate solution. Solutions were prepared as follows; 0.002M potassium tetraoxomanganate solution prepared by measuring 25cm3 of 0.02M potassium tetraoxomanganate solution stock into a 250ml volumetric flask followed by 25cm3 of 2M sulphuric acid and the volume made up to the mark with distilled water, 1% potassium trioxalatoaluminate (III) solution prepared by measuring 0.5g of the product stock into 50ml of distilled water in a volumetric flask. No indicator was necessary since in this case, the intense purple color of the permanganate ion serves as a built-in indicator. The percentage yield of potassium trioxalatoaluminate (III) as well as the percentage of oxalate ligand in the product was calculated using stoichiometry. The percentage yield of the 1.103g of product was found to be 64.3%.The percentages of oxalate ligand were found to be 40.18, 39.72, 39.49 and 39.03 in the product. Actual mean composition of oxalate ligand by percentage was found to be 73.5 ± 0.4787%with variance of 0.2292 for the product. Theory Potassium trioxalatoaluminate (iii) is a metal complex formed between aluminium and oxalate ions both bonded to potassium as the central metal ion. According to J.D.Lee, a complex is formed when transition elements have an un parallel tendency to form co-ordination compounds with groups which are able to donate an electron pair. These groups are called ligands. The most important octahedral complex are formed with chelating ligands for example the reaction between aluminium and oxalate ions gives a complex [Al(C2O4)3]. 2Al(s) + 3C2O42-(aq)
2[Al(C2O4)3]3-(aq)
In the synthesis of potassium trioxalatoaluminate, aluminium is reacted with potassium hydroxide to form a complex and later oxalic acid is introduced to provide the oxalate ions in the solution and also neutralizes the potassium hydroxide in solution. Al(s) + 3KOH(aq) +H2C2O4 •3H2O(aq)
K3[Al(C2O4)3]•3H2O(aq) + 6H2O(l) + H2(g)
We are required to determine the concentration of the oxalate ions in solution, this will involve the introduction of potassium permanganate as the reducing agent through titration with oxalate ions in solution. The oxalate ion reduces the permanganate ions (MnO4ˉ) to Mn2+ which is nearly a colourless solution and the oxalate ions are oxidized to carbon dioxide. This is called a redox reaction where both ©Kwihangane Anne
12/X/25708/Ps
Page 2
reduction and oxidation take place. Reduction is the addition of electrons while oxidation is the removal of electrons. No indicator is required during titration because the purple colour of the permanganate serves as a built in indicator. 16H+(aq)+ 5C2O42-(aq)+ 2MnO4-(aq)
10CO2(g)+ 2Mn2+(aq)+ 8H2O(l)
In this practical we are provided with aluminium sulphate hexahydrate and first reacted with sodium hydroxide to form a precipitate according to the equation; Al2(SO4).16H2O(aq) + 6NaOH(aq)
2Al(OH)3(s) + 3Na2SO4(aq) + 16H2O(l)
Oxalic acid is introduced in the solutions to provide an acid medium and potassium oxalate is also added to provide the oxalate ions and also provide the potassium ions that are required to form the complex which is potassium trioxalatoaluminate (iii); 2Al(OH)3(s) + 3H2C2O4.2H2O(aq) + 3K2C2O4(aq)
2K3[Al(C2O4)3](aq) + 12H2O(l)
Procedure Aluminium sulphate hexahydrate (3.5g) were dissolved in water (25cm3) and to this solution, a solution of sodium hydroxide (1.5g in10cm3 of water) was added while stirring to produce an hydroxo complex. The freshly precipitated alumimium hydroxide was filtered off and washed with (3×20cm3) of water. This precipitate was boiled with aqueous solution of oxalic acid dehydrate (2.5g) and potassium oxalate which was first prepared by dissolving them in water (50cm3) to introduce oxalate ions in the solution. Any un-reacted aluminium hydroxide was filtered off and then the filtrate was evaporated to a volume that could affect crystallization. The potassium trioxalatoaluminate (iii) was filtered off, washed with cold water and then dried in the oven at 70oC. The potassium trioxalatoaluminate(iii) was weighed after cooling in the disiccator and this mass was used to calculate the percentage yield, the sample was submitted in for inspection. To investigate the effect of sodium hydroxide on the small volumes of the potassium trioxalatoaluminate (iii), a small volume was put in the test tube and sodium hydroxide (2M) solution was added and the effect was noted. The procedure was repeated for sodium hydroxide (4M), sodium ethanoate (2M), sodium carbonate (2M). The experiment was performed on aluminium sulphate solution using the same concentration of the reagents to compare the results with that of the potassium trioxalatoaluminate(iii). Potassium trioxalatoaluminate (iii) (1g) was put in a small volumetric flask (100ml) and dissolved in water up to the mark. The solution of the product (10ml) were measured and placed in a conical flask. The potassium permanganate in the burette was ran into the flask until the colour of the solution in the flask changed to pink. The volume of potassium permanganate used was measured and noted. The procedures were repeated for replicated values of potassium permanganate and were recorded in the table. The results obtained were used to calculate the percentage yield of the oxalate ion present in the solution. ©Kwihangane Anne
12/X/25708/Ps
Page 3
When preparing potassium permanganate wear gloves because it is a strong oxidant and it stains both skin and clothes also sulphuric acid should be handled with care because it is corrosive and damages the skin when ed. One end of a capillary tube was sealed and a small amount of the product was inserted through the open end and later the tube was tied on the thermometer. The later was inserted in the beaker containing liquid paraffin. The whole set up was placed on the heat source while stirring to determine the melting point of the potassium trioxalatoaluminate. The temperature at which the first portion of the sample melted was recorded and the temperature when the whole sample melted was recorded. The melting point of the potassium trioxalatoaluminate was determined.
©Kwihangane Anne
12/X/25708/Ps
Page 4
Results Mass of samples used Mass (g)
Mass of container (g) Mass of container + sample (g) Mass of sample used (g)
Aluminium sulphate hexacahydrate 1.994
Sodium hydroxide
Oxalic acid
Potassium oxalate
1.995
1.995
1.994
5.484
3.495
4.477
5.493
3.490
1.500
2.482
3.499
Weight of the product Mass of container (g) Mass of container + product (g) Mass of product only (g)
1.995 4.245 2.250
Effect of the reagents on the product Reagent Sodium hydroxide (2M) Sodium hydroxide (4M) Sodium ethanoate Sodium carbonate Sodium orthophosphate
Observation No observable change No observable change No observable change No observable change No observable change
Effect of the reagents on simple aluminium sulphate Reagent Sodium hydroxide(2M) Sodium hydroxide (4M) Sodium ethanoate(2M) Sodium carbonate(4M) Sodium orthophosphate
©Kwihangane Anne
Observation White precipitate was formed soluble in excess White precipitate was formed soluble in excess No observable change White precipitate was formed soluble in excess White precipitate insoluble in excess
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Melting point of the product Initial temperature = 287˚C Final temperature =289˚C Melting point = = = 288˚C
Treatment of results Percentage yield = = = 64.3% 1000ml of solution contain 0.02 moles of MnO42- ions 16.80ml of solution contain
16.80 moles of MnO42- ions
=0.000336moles of MnO42- ions 2MnO42-(aq) + 5C2O42-(aq) + 16H+(aq)
10CO2(aq) + 2Mn2+(aq) + 8H2O(l)
2moles of MnO42- ions react with 5 moles of C2O4 ions 0.000336 moles of MnO42- ions react with
0.000336 moles of C2O42- ions
= 0.00084moles of C2O42- ions RFM of C2O42- = (12 2) + (4 16) = 88 Mass of the oxalate ions = Number of moles = 0.00084
RRM
88
0.0739g % of oxalate ions =
100% 100%
©Kwihangane Anne
12/X/25708/Ps
Page 6
= 73.9%
Discussion During re-crystallization of the product Ethanol would be used because it eliminates the impurities that might otherwise escape with the final product. So the impurities in this compound may have raised the melting point of the product thus resulting into a higher value. The thread to use when tying the thermometer with the capillary tube should be strong in order to overcome the high temperature of the liquid paraffin, probably the sisal thread can be recommended.
Conclusion The experiment was successful as the complex was prepared and its melting point found without difficulty. Potassium trioxalatoaluminate (III) is a metal complex of aluminium and three ligands, all bonded to a central cation (potassium ion). Each of the three ligands binds to the metal atomt different places thus, bidentate ligands.
The melting point of potassium trioxalatoaluminate(III) was determined as 302.5oC which is in the range of the theoretical value of its melting point.
Reference J.D.Lee (1991) Concise Inorganic Chemistry, 4thedition Chapman and Hall Pg (170, 657) G. and H. Sutcliffe (1974) Practical Inorganic Chemistry, 2nd edition, Chapman and Hall.Pg (10-11) ©Kwihangane Anne
12/X/25708/Ps
Page 7
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