Preparation of Potassium Ferric Oxalate

Dhristi JEE 2022-24

Introduction

Potassium Ferric Oxalate crystal is an inorganic complex that is light green in color and is prepared in the presence of oxalic acid from ferric sulfate and barium oxalate. This is one of the examples of an Oxidation-Reduction reaction.


Potassium Ferric Oxalate is also called Potassium ferrioxalate, Potassium Trioxalatoferrate (III), Potassium tris (oxalato) ferrate(III), and Potassium iron(3+) oxalate.


Aim

To prepare the pure Potassium Ferric Oxalate from three chemicals such as potassium monohydrate, oxalic acid, and ferric chloride dihydrate.


Theory

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


The chemical reactions,


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)


Ferric hydroxide gets dissolved and the soluble complex is formed when the oxalic acid is added excessively. To precipitate the complex iron salt alcohol is added to the solution, as it is less soluble in alcohol than water.


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

Procedure

  1. Dissolve 3.5g of freshly prepared ferric chloride in 10 ml of water, in a beaker.

  2. Dissolve 4g of potassium hydroxide in another beaker with 50ml of water.

  3. With constant stirring, slowly add the potassium hydroxide solution to the ferric chloride solution to form a brown color ferric hydroxide precipitate.

  4. Through the funnel, filter the ferric hydroxide precipitate and wash it with hot water.

  5. Take 4g of oxalic acid and 5.5g of potassium oxalate in another beaker. Add 100ml of water and stir it well to get a clear potassium oxalate solution.

  6. To potassium oxalate solution, gradually add the freshly prepared ferric hydroxide precipitate by stirring it constantly so that precipitate dissolves completely and the green color solution is formed.

  7. Remove the insoluble impurities by filtering the solution.

  8. Take a china dish and transfer the green-coloured solution into it and concentrate the solution till the crystallization point is reached.

  9. In cold water, place the china dish and let it cool for an hour.

  10.  Green crystals of potassium ferric oxalate are formed. From the mother, liquor removes all the crystals.

  11.  With ethyl alcohol, wash the crystals and dry them between the folds of filter paper.

  12.  To know the yield, weigh the crystals.


Observations


Color of the crystals

Green color

Shape of the crystals

Octahedral

Melting point

230oC

Expected yield

10 gm


Results and Discussion:

The Potassium ferric oxalate yield is _______gm.


Precautions

Do not concentrate too much on the solution.


To get big crystals during crystallization, do not disturb the solution.


To dissolve unwanted salt, wash the crystals with hot water.

FAQs on Preparation of Potassium Ferric Oxalate

1. Give the chemical reaction for the preparation of Potassium Ferric Oxalate?

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


The chemical reactions,


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

2. What is the aim, precautions and materials required for the experiment?

Aim:
To prepare the pure Potassium Ferric Oxalate from three chemicals such as potassium monohydrate, oxalic acid, and ferric chloride dihydrate.


Precautions:
Do not concentrate too much on the solution.


In order to get big crystals during crystallization, do not disturb the solution.


In order to dissolve unwanted salt, wash the crystals with hot water.


Materials Required:
Oxalic acid hydrate, Ferric chloride, Potassium oxalate, Potassium hydroxide, Beaker, Conical flask, Tripod stand, Glass rod, Wire gauze, Filter paper, China dish, Funnel.

3. What is the procedure for preparation of Potassium Ferric Oxalate?

Dissolve 3.5g of freshly prepared ferric chloride in 10 ml of water, in a beaker. Dissolve 4g of potassium hydroxide in another beaker with 50ml of water. Slowly add the potassium hydroxide solution to the ferric chloride solution to form a brown color ferric hydroxide precipitate. Filter the ferric hydroxide precipitate and wash it with hot water. Take 4g of oxalic acid and 5.5g of potassium oxalate. Add 100ml of water and stir it well to get a clear potassium oxalate solution.


Add the freshly prepared ferric hydroxide precipitate by stirring it constantly so that precipitate dissolves completely and the green color solution is formed. Remove the insoluble impurities. Transfer the green-coloured solution into it and concentrate the solution till the crystallization point is reached. Cool the china dish. Green crystals of potassium ferric oxalate are formed. Remove all the crystals. Wash the crystals and dry them.

4. What is Potassium Ferric Oxalate?

Potassium Ferric Oxalate crystal is an inorganic complex that is light green and is prepared in the presence of oxalic acid from ferric sulfate and barium oxalate. This is one of the examples of an Oxidation-Reduction reaction.


Potassium Ferric Oxalate is also called Potassium ferrioxalate, Potassium Trioxalatoferrate (III), Potassium tris (oxalato) ferrate(III), and Potassium iron(3+) oxalate.


Potassium ferric oxalate is considered a complex compound with the chemical formula of K3 [Fe(C2O4)3].3H2O.


Ferric hydroxide gets dissolved and the soluble complex is formed when the oxalic acid is added excessively.

5. How is Potassium Ferric Oxalate used in blueprints?

Before the ready production of large ink-jet and laser printers, large-scale engineering sketches were widely replicated using the cyanotype process.


That was an easy contact-based photographic method that produced a "negative" white-on-blue copy of the original drawing, which is a blueprint. The method was based on an iron (III) complex photolysis, which turned it into an insoluble iron (II) version in the paper areas exposed to light.


The complex that is used in the cyanotype is primarily ammonium iron(III) citrate, whereas potassium ferrioxalate is also used.

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