PPA1 Preparation of Potassium Trioxalatoferrate

(NH4)2Fe(SO4)2.6H2O         → 2K3(Fe(C2O4)3) + 6H2O

Molar ratio                              1    :      1

Actual Yield                          4.86g

mol= 0.0128 mol -1                                mol= 0.0128 mol -1        

mass= 5.03g                                                    mass=6.28g                                                                                        

GFM= 392g                                                    GFM= 491.1

Mol= mass/GFM                                         Mass= GFM x mol

Mol=5.03/392                                             Mass= 491.1 x 0.0128

Mol= 0.0128                                               Mass= 6.28g

                                                        Theoretical Yield = 6.28g

Percentage Yield =Actual Yield        x 100

                       Theoretical Yield

                    = 4.86g  x 100

                        6.28g        

                    = 77.39%

Discussion

a) Reasons for the fact the yield of Potassium Trioxalatoferrate are less than 100% are:    

• Products may be  lost during the decanting stage
• Products may be washed away
• Products may be left on filter paper
• Products may react with chemicals in the beakers from previous experiments

b) Hydrogen Peroxide is used in the preparation of Potassium Trioxalatoferrate as it is an extremely strong oxidising agent. This reduces iron (II) ions to iron (III) ions.

Procedure

• A 100 cm3  glass beaker was weighed and approximately 5g hydrated ammonium iron(II) sulphate was added. The beaker and its contents were then reweighed.
• Approximately 15 cm3 and 1 cm3  sulphuric acid were added to the ammonium iron(II) sulphate. The mixture was then warmed to dissolve the solid
• After the ammonium iron(II) sulphate was dissolved 25 cm3 oxalic acid was added.

   

(NH4)2Fe(SO4)2.6H2O + H2C2O4 → FeC2O4 + H2SO4 + (NH4)HSO4 +6H20

                        Green              →       Yellow

• The beaker was then placed on a hot plate and slowly heated and stirred until it boiled.
• The beaker was removed from the heat in order to allow the precipitate (Iron (II) Oxalate) to form at the bottom of the beaker.
• The liquid was then decanted and 50 cm3 of deionised water was added to the remaining precipitate. The mixture was then stirred, this allowed the precipitate to settle again, and then it decanted again.
• 10 cm3 of Potassium Oxalate was added to the washed precipitate and heated to 40º C.
• 20 cm3  “20 Volume” Hydrogen Peroxide was added to the solution. The temperature was kept as close as possible to 40º C.

6FeC2O4 + 3H2O2 + 6K2C2O4 → 4K3[Fe(C2O4)3] + 2Fe(OH)3

                        Yellow →  Brown/Orange

• The mixture was heated until it nearly reached boiling point, oxalic acid was then added drop by drop until the brown precipitate had disappeared.

      2Fe(OH)3 + 3H2C2O4 +3K2C2O4 → 2K3(Fe(C2O4)3) + 6H2O

                        Brown/Orange → Green

• The hot solution is filtered through fluted filter paper into a crystallising basin
• 25 cm3 of Ethanol is added to the filtrate and any crystals that formed were dissolved by gentle heating.
• The solution was covered and stored in a dark cupboard to allow crystallisation to occur.
•  The crystals were filtered then washed with a 1 : 1 mixture of Ethanol and water.
• The crystals were weighed in a clock glass and then covered with filter paper and retuned to the cupboard.
• Once dry, the crystals and clock were reweighed.
• The percentage yield of hydrated Potassium Trioxalatoferrate was calculated.

Hazards

Eye protection was worn and if any chemicals were splashed onto skin it was washed off immediately. Cation was taken at all times to wear the safety equipment provided, in this case safety goggles and latex gloves.