Inorganic Chemistry

Transition elements contain ions that present in aqueous solution as complex ions. A metal ion with a molecule called a ligand are called complex ion and it attached through coordinate covalent bonds. A complex salt is an ionic compound but it differs in the fact that there are these covalent bonds attaching the metal to the ligand. For example in iron(II) ion, it exists in water as Fe(H2O)62+. In this ion, water molecules are arranged about the iron atom with their oxygen atoms bonded to the metal by donating electron pairs to it. A coordination compound is a compound that have either of complex ions and other ions of a neutral species or opposite charge.

As an example of coordination compound is the compound K4[Fe(CN)6] which contains the complex ion Fe(CN)6 4- and four K+ ions. Some of the transition elements have biological activity and their role in human nutrition depends in most cases on the formation of complexes and coordination compounds. In this experiment, three compound were prepared which are potassium tris(oxalate)chromium(III) trihydrate# copper(II)oxalate complex and potassium tris(oxalate)ferrate(III) trihydrate. The amount of coordination compound expected from a given mass of reactants can be calculated and is called the theoretical yield . The percentages of yield are calculated at the end by dividing the actual yield with its theoretical and multiply with 100.

Procedure
Experiment 3
About 5.00 g of oxalate acid was dissolved in 1% ml distilled water in a conical flask. 1.8 g of potassium dichromate was added into the mixture in small portions and the funnel was placed on the mouth of conical flask.
After the reaction had stopped, 2.10 g of potassium oxalate monohydrate was added into the hot green black liquid and it was heated until boiling for 5 minutes.
The flask was cooled down at room temperature and 10 ml of 95% ethanol was added into the flask and it was cooled in ice bath with frequent stirring.
After cooling in ice for 15 minutes or when the precipitate completely formed, the precipitate was collected by suction filtration.
The crystals were washed with 5 ml portion 1:1 ethanol-distilled water and followed by 13 ml of 95% ethanol.
The crystals were placed on the watch glass and it was allowed to dry in the oven.
The mass of the synthesis crystals and percentage yield were determined.
The crystals were transferred into a plastic packet. It was kept for next experiment.

Experiment 4
2.00 g of copper(II) sulphate was weighed and it was placed in conical flask. 30 ml of distilled water was added in the flask. The flask was heated slowly on a hot plate until the solid dissolves.
6.20 g of potassium oxalate monohydrate was dissolved in 30 ml of distilled water in another flask.
The heated CuSO4 solution was added slowly into the flask that contained potassium oxalate monohydrate. The flask was swirled slowly to mixed.
The mixture was cooled in ice bath for 30 minutes. Blue crystals were formed.
The crystals were placed on the watch glass and it was allowed to dry in the oven.
The mass of the synthesis crystals and percentage yield were determined.
The crystals were transferred into a plastic packet. It was kept for next experiment

Experiment 5
Procedure (A)
5.00 g of ferrous ammonium sulphate was dissolved in 25 ml distilled water containing 1 ml of diluted sulphuric acid in the beaker.
2.5 g of oxalate acid dihydrate was dissolved in 25 ml of distilled water in another beaker. Then it was added into the beaker containing ferrous ammonium sulphate
The mixture was heated slowly until boiling and then the yellow precipitate was allowed to settle down . The supernatant was discarded. 15 ml hot water was added into the yellow precipitate. It was stirred and the supernatant was discarded.

15 ml of hot water was added to precipitate. 3.5 g of solid potassium oxalate monohydrate was added. It was heated to approximately 40°C.

Then immediately 10 ml of 10% H2O2 was added drop wisely and it was stirred continuously.
It was heated to boiling and the dissolved solution of 2.0 g of oxalic acid in 30 ml of distilled water was added into the mixture until the brown precipitate was dissolved.
It was boiled until the solution was clear. The solution was filtered through buchner funnel. 3o% ml of 95% ethanol was added slowly to the solution. Any crystals that are formed was redissolved. Then it was leaved for storage that are not exposed direct light to crystallise for a week.

Procedure (B)
The crystals were collected by suction filtration process. The beaker was rinsed with 10 ml of 1:1 ethanol-distillation water for two times. The crystals were washed with cold acetone.
The crystals were placed on the watch glass and it was allowed to dry on air.
The mass of the synthesis crystals and percentage yield were determined
The crystals were kept for next experiment.

Result
Experiment 3:
Mass of K2Cr2O7 1.8029 g
Mass K2C2O4. H2O 2.107 g
Mass of glass watch + filter paper 32.451 g
Mass of glass watch + filter paper + K3[Cr(C2O4)3].3H2O 35.345 g
Mass of K3[Cr(C2O4)3].3H2O 2.894 g
Theoretical yield 5.9706 g
Percent yield 48.47 %
Experiment 4:
Mass CuSO4.5H2O 2.0546 g
Mass K1C2O4.H2O 6.2194 g
Mass of glass watch + filter paper 31.5282 g
Mass of glass watch + filter paper + copper (II) oxalate 33.4469 g
Mass of crystal 2.9011 g
Theoretical yield 1.9187 g
Percent yield 66.14%
Experiment 5:
Mass of Fe(OH)4 5.1095 g
Mass of K2C2O4 3.4984 g
Mass of filter paper 0.3357 g
Mass of glass watch + filter paper + K2[Fe(C2O4)3].3H2O 3.4148 g
Mass of crystal 3.0791 g
Theoretical yield 6.9231 g
Percent yield 44.48%
Calculation
Experiment 3
Theoretical mass of K2[Cu(C2O4)2(H2O2)]
No. of mole K2Cr2O7 = massmolar mass = 1.8029 g294 g/mol = 0.00613 molNo. of mole K2C2O4 .H2O = massmolar mass = 2.107 g 184 g/mol = 0.01145 molThus, the limiting reactant is K2Cr2O7
From chemical equation below:
H2C2O4 + K2Cr2O7 + K2Cr2O7 2 K3[Cr(C2O4)3].3H2O + 4CO2 + 3H2O
1 mol of K2Cr2O7= 2 mol of K3[Cr(C2O4)3].3H2O
0.00613 mol of K2Cr2O7 = 0.01226 mol of K3[Cr(C2O4)3].3H2O
Theoretical mass of of K3[Cr(C2O4)3].3H2O
= no. mol of K3[Cr(C2O4)3].3H2O x molar mass
= 0.01226 mol x 487 g/mol = 5.9706 g
Percent yield of of K3[Cr(C2O4)3].3H2O = actual theoretical x 100
= 2.894 g 5.9796 x 100
= 48.47 %
Experiment 4
Theoretical mass of K2[Cu(C2O4)2(H2O2)]
No. of mole CuSO4.5H2O = massmolar mass = 2.0546 g250 g/mol = 0.0082 molNo. of mole K1C2O4.H2O = massmolar mass = 6.2194 g 184 g/mol = 0.0338 molThus, the limiting reactant is CuSO4.5H2O
From chemical equation below:
CuSO4.5H2O + K1C2O4.H2O K2[Cu(C2O4)2(H2O2)] + K2SO4 + 5H2O
1 mol of CuSO4.5H2O = 1 mol of K[Cu(C2O4)2(H2O2)]
0.0082 mol of CuSO4.5H2O = 0.0082 mol of K2[Cu(C2O4)2(H2O2)]
The theoretical mass of K2[Cu(C2O4)2(H2O2)] = no. mol K2[Cu(C2O4)2(H2O2)] x molar mass
= 0.0082 mol x 352 g/mol = 2.8864 g
Percent yield of of K2[Cu(C2O4)2(H2O2)] = actual theoretical x 100
= 1.9187 g 2.8864 x 100
= 66.47 %

Experiment 5
Theoretical mass of K3[Fe(C2O4)3].3H2O
No. of mole K2C2O4 = massmolar mass = 3.4984 g166 g/mol = 0.0211 molNo. of mole Fe(OH)4= massmolar mass = 5.1095 g 124 g/mol = 0.0416 molThus, the limiting reactant is K2C2O4
From chemical equation below:
3K2C2O4 + 2Fe(OH)4 + 3H2C2O4 2 K3[Fe(C2O4)3].3H2O + 3H2O
3 mol of K2C2O4 = 2 mol of K3[Fe(C2O4)3].3H2O
0.0211 mol of K2Cr2O7 = 0.0141 mol of K3[Cr(C2O4)3].3H2O
Theoretical mass of of K3[Fe(C2O4)3].3H2O
= no. mol of K3[Fe(C2O4)3].3H2O x molar mass
= 0.0141 mol x 491 g/mol = 6.9231 g
Percent yield of of K3[Fe(C2O4)3].3H2O = actual theoretical x 100
= 3.0791 g 6.9231 G x 100
= 44.48 %

Discussion

In experiment 3, the coordination compound which is potassium tris (oxalato) chromium (III) trihydrate, K3[Cr(C2O4)3].3H2O are synthesized. The experiments were started by adding potassium dichromate, K2Cr2O7 into acidic solution which are oxalic acid. The mixtures are warmed up immediately after added and it result in orange coloured solution. When potassium oxalates were further added, the solution changes its colour into dark green. The chemical equations of the reaction are expressed as followed

H2C2O4 + K2Cr2O7 + K2Cr2O7 2 K3[Cr(C2O4)3].3H2O + 4CO2 + 3H2O
The crystals of emerald or dark green colour are formed when it was filtered and washed with 1:1 ethanol/water and followed by 13 ml of 95% ethanol. The dark green crystal were known as K3[Cr(C2O4)3].3H2O . The chromium(iii) in the coordination compound are the most stable oxidation state of chromium as it formed a number of complexes in which six monodentate ligands surround the cation octahedral manner. The actual or experimental weight of the crystal are 2.894 g. Based on calculation, the theoretical weight of K3[Cr(C2O4)3].3H2O are 5.9706 g. Thus, the percentages of yield are calculated by dividing the actual mass with its theoretical mass and multiply with 100. The percentage of yield that was calculated is 48.47 % which are considered as low. There is 51.53% different than the total percent of yield which occurred due to some errors. One of the errors was due to incomplete reaction during the mixing of reactants. Besides, the mixture of K3[Cr(C2O4)3].3H2O may not be cooled enough during the precipitation process. Thus, the amount of crystal formed after filtrations are decreased.

In experiment 4, the coordination compound that are synthesized are copper (II) oxalate complexes, K2[Cu(C2O4)2(H2O2)] in which copper are known as a transition element. The experiments are started by reacting copper (II) sulphate pentahydrate, CuSO4.5H2O with potassium monohydrate, K1C2O4.H2O. The mixture must be heated afterwards. The crystal formed after the solutions are cooled in ice bath which result in blue coloured crystal.

The chemical equation of the reactions are expressed as followed:
CuSO4.5H2O + K1C2O4.H2O K2[Cu(C2O4)2(H2O2)] + K2SO4 + 5H2O
The crystal were filtered, washed and dried. The experimental weight of the crystal or K2[Cu(C2O4)2(H2O2)] are 2.9011 g. Based on calculation, the theoretical weight of K2[Cu(C2O4)2(H2O2)] are 1.9187 g. Thus, the percentages of yield are calculated by dividing the actual mass with its theoretical mass and multiply with 100. The percentage of yield that was calculated is 66.14 % which are slightly above than half of the total of yield.

In experiment 5, the coordination compound which are potassium tris (oxalato) ferrate (III) trihydrate, K3[Fe(C2O4)3].3H2O were synthesized. The experiment begun by adding ferrous ammonium solution with the oxalic acid dihydrate and a yellow precipitate are formed. The chemical equation that takes place is as followed:

Fe(NH4)2(SO4)2.6H2O + H2C2O4 FeC2O4 + H2SO4 + (NH4)2SO4 + 6H2O
The solutions are then heated until boiling and the yellowish supernatant are discarded. Potassium oxalates are added exacty at 40 C while H2O2 are added dropwise. The solution formed a precipitate with dark brown colour. It occurred due to the oxidation of ferrous ion into ferric ion. The reactions are shown in the following chemical equation:
H2O + HO2 – + 2 Fe2+ 2Fe3= + 3OH-
Fe3+ + 3OH- Fe(OH)3
Lastly, oxalic acid dihydrate were added into the mixture solution to dissolve the brown precipitate. The solutions are then turned into light green colour. Crystal are filter by suction and washed with 30 ml of 95% ethanol followed by 1:1 of ethanol/water. The experimental weight of K3[Fe(C2O4)3].3H2O are 3.0791g. Based on the calculation, the theoretical yield of of K3[Fe(C2O4)3].3H2O are 6.9231 g. The percentage of yield that was calculated is 44.48 % which are slightly lower than half of the total of yield. Some of the error that occurs might be during the process of heating where the solutions were not heated to the boiling temperature which result an incomplete reaction. Some of the precaution that should be taken is to make sure that the apparatus used are free from impurities to avoid contamination. Other than that is to avoid loss of product mass during the transferring and heating process.

Conclusion
In conclusion, the coordination compound such as potassium tris (oxalato) chromium (III) trihydrate , copper (II) oxalate complex and potassium tris (oxalato) ferrate (III) trihydrate were synthesized. Their actual mass were obtained from the experimental yield while the theoretical yield are calculated manually. The percentage of yield are then calculated which are 48.47 %, 66.14% and 44.48% for K2[Cu(C2O4)2(H2O2)] , K2[Cu(C2O4)2(H2O2)] and K3[Fe(C2O4)3].3H2O respectively.
References
Introduction to coordination chemistry. Retrieved November 7, 17 from https://aassofia.files.wordpress.com/2013/12/introduction_coordination_chemistry-ibchemlab.pdfSynthesis of coordination compound. Retrieved November 7, 17 from http://chemistry.bd.psu.edu/jircitano/labsynfes034.pdfQuestions
What is the oxidation state of chromium in K2Cr2O7 and in the product?
298474071084003056255105410K3[Cr(C2O4)3].3H2O = 0
(+1)(3) + (x)+ (-2)(3)+ (3)(0)= 0
X = +6 – 3 = +3
Thus, oxidation state of chromium for product is +3
020000K3[Cr(C2O4)3].3H2O = 0
(+1)(3) + (x)+ (-2)(3)+ (3)(0)= 0
X = +6 – 3 = +3
Thus, oxidation state of chromium for product is +3

K2Cr2O7 = 0
(+1)(2) + (x)(2) + (-2)(7) = 0
2x = 14 – 2
X = +6

Thus, oxidation state of chromium is +6.Write two half equation for each reaction involved in the preparation of the complex using oxalic acid dehydrates, K2C2O4. H2O and potassium dichromate, K2Cr2O7 and a balanced equation for the overall equation.
Half equation :5C2O42- 10CO2 + 10 e
Cr2O72- + 14H+ + 10e 2Cr2+ + 7H2O
Overall equation:
5C2O42- + 14H+ + Cr2O72- 10CO2 + 2Cr2+ + 7H2O