in pH. In some cases, [Fe(C 2 O 4 ) 2 ] 3– forms, and in other cases it is destr
ID: 562132 • Letter: I
Question
in pH. In some cases, [Fe(C2O4) 2]3– forms, and in other cases it is destroyed. What is happening on the molecular level? What conditions favour its formation and what favour its destruction?
Scheme I Ir Felll O)l" (2) SCN [Fe(SCN)J (3) (Fe(SCN).] (3) [FeFal" (4) FeF J (4) Place I mL of the green solution I in a test tube and add 3 drops of 6 M HCl: the solution turns yellow-orange (2) to 2 add 3 drops of 0.5 M KSCN; the solution turns red (3) . to 3 add 10 drops of 3 M KF, the solution becomes almost colorless (4) to 4 add 15 drops of 2 MK,C,O, the green solution I is obtained again Scheme2 oir Ba* Fe(SO) Baco, (B) [Fe(C,04b]. (1) + Baso, (c) Place I mL of the green solution I in a test tube and add I mL of 0.I M NaOH to I mL of solution I slowly! A brown precipitate (A) and a colorless solution (6) are obtained that can be separated by centrifugation (3 minutes) or filtration. (Do you think you should wash the precipitate? If so with what?) Shaking the brown solid A with I mL of I M H,C,O, gives the green solution I again. Treatment of the colorless solution 6 with I mL of 0.2 M BaCh gives a white precipitate After centrifugation or filtration, the white solid B is treated with 10 drops of I M Fe,(SO), Centrifugation gives the green solution I again and a white precipitate (C). CHE204-Laboratory Manual-2017 Expt IS2- Page 3 of 4 02017Farmer, C Anbidge & TP BenderExplanation / Answer
Scheme I
[Fe(C2O4)3]3+ + H+ -----------> [Fe(H2O)6]3+ + H2C2O4
When [Fe(C2O4)3]3+complex is treated with acid like oxalic acid, EDTA etc. The free H+ ion concentration is decreased due to formation of H2C2O4, hence the pH of the reaction solution increases.
Scheme II
[Fe(C2O4)3]3+ + OH- -----------> [Fe(OH)3] + C2O42-
When [Fe(C2O4)3]3+ is treated with basic solution it forms ferric hydroxide and oxalate ion, the H+ ion concentration is low concentration of OH- is high so, the pH of the solution increases.
[Fe(OH)3] + H2C2O4 ------------>[Fe(C2O4)3]3+ + H+
When ferric hydroxide is again made to react with oxalic acid, [Fe(C2O4)3]3+ is formed, simultaneously the concentration of H+ ions increases and the pH decreases.
Conclusion:
a.The [Fe(C2O4)3]3+ is sustained when solution has low pH i.e. is acidic.
b.The [Fe(C2O4)3]3+ is destroyed if the pH of the solution increases.
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