ethanedioate complex of iron

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Title: The preparation, analysis, and reactions of an ethanedioate complex of iron

Objective:

* To prepare oxalate complex of iron from the reaction with ammonium iron (II) sulphate

* To deduce the oxidation states of iron in the complex

* To determine the amount of iron and oxalate in the oxalate complex of iron by

titration.

* To investigate the molecular formula of the complex formed by preparation, analysis and the reaction of an ethanedioate (oxalate) complex of iron

* To deduce the chemical properties of the complex of iron from the reactions with dilute sodium hydroxide, ammonium thiocyanate solution, and ammonium

thiocyanate solution in the presence of dilute sulphuric acid respectively, compared to the reaction of iron(III) chloride and the reagents above.

Introduction

Iron is nearly always determined by reduction to the dipositive state followed by titration with manganate(VII) or dichromate(VI). However oxalate would interfere and must be determined first by titration with permanganate. After titration, any iron present will be Fe(III) then reduced by tin(II) chloride and hydrochloric acid, and the Fe(II) determined with dichromate.

Materials and Methods

Procedure for prepartion

10.53g of ammonium iron(II) sulphate, (NH4)2Fe(SO4)2?6H2O , was weighed using a rough balance and put into a 400cm3 beaker, followed by the addition of few drops of dilute sulphuric acid and 30cm3 of water, and heated until a clear solution was obtained. Then a solution of 5.08g oxalic acid dihydrate in 30cm3 of water was added. The mixture was heated cautiously, with continuous stirring to boil. Then the yellow precipitate of hydrated iron(II) oxalate was allow to settle. The supernatant liquid was poured off and the precipitate was washed once with hot water by decantation. A hot solution of 7.49g of potassium oxalate monohydrate in 20cm3 of water was added and the mixture was cooled to 40?. 20cm3 of 6% hydrogen peroxide solution was added a few drops at a time with continuous stirring. The temperature must be kept below 50?. Then the mixture was heat to the boiling point and 2.503g of oxalic acid dihydrate was added. After stirring for 2-3 minutes, a clear green solution was obtained. Then, it was filtered using a filter paper and a long-stemmed funnel. 10cm3 of 95% ethanol was added to the clear solution to redissolve any precipitated crystals by warming on a steam bath. The solution bottle was then covered by aluminum foil and was set-aside in a dark cupboard for crystallization to occur. The crystals were separate by filtration using a sintered-glass funnel. Then it were washed twice with a mixture of equal volumes of ethanol and water, and followed by twice with acetone. The solid was allowed to air dry by suction. The weight of the dry solid was weighed and the yield was calculated.
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Procedure for Analysis

(a)Oxidation with permanganate

Two portions of 0.38g of the sample complexes were added into two conical flasks separately. Each sample was dissolved in 10cm3 of water and 15cm3 of dilute sulphuric acid. When the solution was heated to 70?, the thermometer was removed and washed down, and was titrated with the standard, approximately 0.02M solution of permanganate. A pink color was persisting for 30 seconds at the end-point. The resulting solution was kept for the determination of iron in (b).

(b)Percentage of iron

15cm3 of concentrated hydrochloric acid was added to ...

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