Preparation of Potassium Ferric Oxalate


Potassium Ferric Oxalate crystals are described as a light green color complex compound that is prepared from barium oxalate and ferric sulfate in the presence of oxalic acid. The preparation of potassium ferric oxalate is given as an example of an Oxidation-Reduction reaction.

The other names of Potassium Ferric Oxalate can be given as Potassium ferrioxalate, Potassium Trioxalatoferrate (III), Potassium tris (oxalato) ferrate(III), and Potassium iron(3+) oxalate.

Preparation of Potassium Ferric Oxalate

Let us know how to prepare potassium ferric oxalate.


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


Potassium ferric oxalate can be prepared when the freshly prepared ferric hydroxide is dissolved in an oxalic acid solution, a yellow precipitate of ferrous oxalate will be produced. Further, it is treated with the potassium oxalate monohydrate; there forms a green precipitate of Potassium Ferric Oxalate. Potassium ferric oxalate is defined as a complex compound having the formula K3[Fe(C2O4)3].3H2O.

The chemical reactions for this compound are given below:

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

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

FeCl3 + 3KOH → Fe(OH)3 + 3KCl

(Potassium Ferric Oxalate)

Oxalic acid is added in an excess amount so that the ferric hydroxide dissolves, and then the soluble complex is produced. Also, alcohol is added to the same solution to precipitate the complex iron salt because it is less soluble in alcohol compared to water.

Materials Required

  • Ferric chloride

  • Oxalic acid hydrate

  • Potassium hydroxide

  • Potassium oxalate

  • Conical flask

  • Beaker

  • Glass rod

  • Tripod stand

  • Filter paper

  • Wire gauze

  • Funnel

  • China dish

Apparatus Setup

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  • Dissolve 3.5 grams of freshly prepared ferric chloride in a beaker in 10 ml of water.

  • Now take another glass beaker and dissolve 4 grams of potassium hydroxide in 50ml of water.

  • Then, slowly add the potassium hydroxide solution to the ferric chloride solution with constant stirring. By doing so, a brown-colored ferric hydroxide precipitate is produced.

  • Filter the ferric hydroxide precipitate via the funnel and then wash the precipitate with hot water.

  • Take 5.5 grams of potassium oxalate and 4 grams of oxalic acid in another beaker. And stir well to get a clear solution of potassium oxalate by adding 100ml of water.

  • Then, gradually, add the freshly prepared ferric hydroxide precipitate to the potassium oxalate solution with constant stirring so that the precipitate completely dissolves and a green-colored solution can be formed.

  • Filter the solution to remove any insoluble impurities.

  • Now, transfer the green-colored solution to a china dish and concentrate the total solution till the crystallization point is achieved.

  • Place the respective china dish in cold water and allow it for cooling for an hour.

  • By doing so, there form green crystals of potassium ferric oxalate. Remove these crystals from the mother liquor.

  • Wash the crystals thoroughly with ethyl alcohol and dry them between the filter paper folds.

  • Now, weigh the crystals to know the yield.


Let us see the observations that are recorded during the experiment:

Shape of the crystals


Colour of the crystals

Green colour

Expected yield

10 grams

Melting point


Results and Discussions

The Potassium ferric oxalate yield is _______ grams.


  • Don't concentrate on the solution too much.

  • While washing the crystals, wash them with hot water to dissolve any unwanted salt.

  • Do not disturb the solution at the time of crystallization to get big crystals.

Uses of Potassium Ferrioxalate

Chemistry Education

The synthesis and the thermal decomposition of potassium ferrioxalate are said to be a popular exercise for college, undergraduate university students, or for high school because it involves the chemistry of transition metal complexes, which is visually observable thermogravimetry, and photochemistry.

Actinometry and Photometry

The discovery of the ferrioxalate anion's efficient photolysis was a landmark for chemical actinometry and photochemistry. Potassium salt has been shown to be more susceptible than 1000 times relative to uranyl oxalate, which is a compound previously used for these purposes.


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.

Adding Hydrogen Peroxide in Potassium Ferric Oxalate Preparation

Potassium ferric oxalate trihydrate is defined as a complex compound. In complex compound synthesis, Hydrogen peroxide (H²O²) is used because this is a typical Oxidation-Reduction reaction. Also, in this reaction, Ferrous ion (Fe²+) will be oxidized to Ferric ion (Fe³+) using Hydrogen peroxide. Also, O- in peroxide is reduced to O²-.

Hydrogen peroxide can be used as an Oxidising agent where it undergoes the reduction in the potassium ferric oxalate synthesis.

FAQs (Frequently Asked Questions)

1. Describe the Color of Potassium Ferric Oxalate and Its Melting Point?

Answer: The melting point of Potassium ferric oxalate is 230 ⁰C, and its color is green.

2. Define the Term Crystallization?

Answer: Crystallization is defined as the process through which a solid form is formed, where either the molecules or atoms are highly organized into a structure, which is called a crystal.

3. What is Meant by the Word "Equilar Proportions?"

Answer: The proportion of the substances in a ratio of their molecules is in the mole ratio of 1:1.

4. Explain the Relation Between Resistance and Specific Conductivity of a Solution?

Answer: The relation between resistance and specific conductivity of a solution is given as Specific conductance = Cell constant x (1/Resistance)

5. What is Meant by the Term "Seeding"?

Answer: In a few cases, the crystallization does not occur if the crystal of a similar substance is added to the saturated solution to induce crystallization. This is known as seeding.

6. Explain if Hydrogen Peroxide is Explosive?

Answer: No. when decomposing to water, the hydrogen peroxide releases oxygen. This can also cause 2 "explosive" problems. First, the oxygen causes combustibles to burn fast, which can ignite fuel in a manner that causes rapid burning. Then, close it in a container, and that reaction may cause an explosion. The second way is just by building up the pressure in a container to the rupture point.