Preparation of Potassium Ferric Oxalate

Potassium Ferric Oxalate crystals is a light green colour complex compound prepared from ferric sulphate and barium oxalate in the presence of oxalic acid. This preparation of potassium ferric oxalate is an example of an Oxidation-Reduction reaction.

Aim:

To prepare the pure samples of crystals of Potassium Ferric Oxalate from oxalic acid dihydrate, potassium monohydrate and ferric chloride.

Theory:

Potassium ferric oxalate is prepared when freshly prepared ferric hydroxide is dissolved in a solution of oxalic acid, a yellow precipitate of ferrous oxalate will be formed. It is further treated with potassium oxalate monohydrate, and a green precipitate of Potassium Ferric Oxalate is formed. Potassium ferric oxalate is a complex compound with the formula K₃[Fe(C₂O₄)₃].3H₂O.

The chemical reactions are given below.

FeCl₃ + 3KOH → Fe(OH)₃ + 3KCl

2Fe(OH)₃ + 3(COOH)₂.2H₂O → Fe₂(C₂O₄)₃ + 12H₂O

Fe₂(C₂O₄)₃ + 3(COOK)₂.H₂O → 2K₃[Fe(C₂O₄)₃].3H₂O

(Potassium Ferric Oxalate)

Oxalic acid is added in excess so that ferric hydroxide dissolves and the soluble complex is formed. Alcohol is added to the solution to precipitate the complex iron salt as it is less soluble in alcohol than water.

Other names – Potassium Trioxalatoferrate (III), Potassium ferrioxalate, Potassium iron(3+) oxalate, Potassium tris(oxalato)ferrate(III)

Materials Required:

1. Oxalic acid hydrate
2. Ferric chloride
3. Potassium oxalate
4. Potassium hydroxide
5. Beaker
6. Conical flask
7. Tripod stand
8. Glass rod
9. Wire gauze
10. Filter paper
11. China dish
12. Funnel

Apparatus Setup:

1. Ferric oxalate solution – Fe₂(C₂O₄)₃
2. Potassium Ferric Oxalate – K₃[Fe(C₂O₄)₃].3H₂O

Procedure:

1. In a beaker dissolve 3.5 g of freshly prepared ferric chloride in 10 ml of water.
2. Take another beaker and dissolve 4 g of potassium hydroxide in 50ml of water.
3. Add the potassium hydroxide solution slowly to the ferric chloride solution with constant stirring. A brown colour ferric hydroxide precipitate is formed
4. Filter the precipitate of ferric hydroxide through the funnel and wash the precipitate with hot water.
5. In another beaker take 4 g of oxalic acid and 5.5 g of potassium oxalate. Add 100 ml water and stir well to get a clear solution of potassium oxalate.
6. Add the freshly prepared ferric hydroxide precipitate to potassium oxalate solution gradually with constant stirring so that precipitate dissolves completely, and the green colour solution is formed.
7. Filter the solution in order to remove any insoluble impurities.
8. Transfer the green-coloured solution to a china dish and concentrate the solution till the crystallisation point is achieved.
9. Place the china dish in cold water and allow cooling for an hour.
10. Green crystals of potassium ferric oxalate are formed. Remove the crystals from the mother liquor.
11. Wash the crystals with ethyl alcohol and dry them between the folds of filter paper.
12. Weigh the crystals in order to know the yield.

Observations:

Results and Discussion:

The yield of Potassium ferric oxalate is _______gm.

Precautions:

1. Do not concentrate the solution too much.
2. Do not disturb the solution during crystallisation in order to get big crystals.
3. While washing the crystals, wash them with hot water in order to dissolve unwanted salt.