Content Curator
Potassium ferric oxalate is a crystalline compound that is lime green in color. We can synthesize crystalline Potassium Ferric Oxalate (K3[Fe(C2O4)3].3H2O) by using chemicals such as oxalic acid, potassium monohydrate, and ferric chloride dihydrate. Potassium ferric oxalate has been used in photometry, actinometry, and to create blueprints (before inkjets and laser printers came into existence).
Read Also: All about solutions
| Table of Content |
Key takeaways: Potassium ferric oxalate, crystallization, seeding, photoreduction, precipitates, hydrates, (K3[Fe(C2O4)3].3H2O).
What is Potassium Ferric Oxalate?
[Click Here for Sample Questions]
Potassium ferric oxalate is a crystalline compound that is lime green in color. The other names for the compound are: Potassium iron(3+) oxalate, Potassium Trioxalatoferrate (III), Potassium tris(oxalato)ferrate(III), and Potassium ferric oxalate. The formula for Potassium ferric oxalate is K3[Fe(C2O4)3] but in nature, it always occurs as a trihydrate. Hence the formula is (K3[Fe(C2O4)3].3H2O).
Crystals of Potassium Ferric Oxalate
The crystalline compound consists of ferric oxalate anions, [Fe(C2O4)3]3−, and potassium cations K+. The anion [Fe(C2O4)3]3− is a transition metal complex which in turn consists of a Fe atom in the +3 oxidation state and three bidentate oxalate ions C2O42- anions which act as ligands. K plays the role of a counterion that balances the −3 charge of the complex. In solution, the salt dissociates to give the fluorescent green ferric oxalate anion, [Fe(C2O4)3]3−. The anion is stable in the dark and will be decomposed by light and high-energy electromagnetic radiation.
Read More: Types of solutions
Structure of Potassium ferric oxalate
[Click Here for Sample Questions]
The structure of the trihydrate implies that the Fe(III) has a high spin. This happens because the low spin complex of the salt tends to display Jahn–Teller distortions. The NH4+, Al3+, Cr3+, and V3+ and mixed sodium-potassium salts are isomorphous.
The ferric oxalate complex forms two non-superimposable geometries and thus displays a helical chirality. According to the IUPAC convention, the isomer with the left-handed screw axis is assigned the Greek symbol Λ (lambda) while the mirror image with the right-handed screw axis is given the Greek symbol Δ (delta).
Structure of Potassium ferric oxalate
Check Also: Electrolytic cell
Preparation of Potassium ferric oxalate
[Click Here for Sample Questions]
The experiment procedure for the preparation of Potassium ferric oxalate is as follows.
Aim
To synthesize crystalline Potassium Ferric Oxalate (K3[Fe(C2O4)3].3H2O) by using chemicals such as oxalic acid, potassium monohydrate, and ferric chloride dihydrate.
Theory
The process for the synthesis of Potassium Ferric Oxalate involves two steps:
A freshly prepared ferric hydroxide-Fe(OH)3 is dissolved in a solution of excess oxalic acid-FeCl3.
Chemical equations:
FeCl3 + 3KOH → Fe(OH)3 + 3KCl
2Fe(OH)3 + 3(COOH)2.2H2O → Fe2(C2O4)3 + 12H2O
Main product formed: Ferrous oxalate- Fe2(C2O4)3
Color of the precipitate: Yellow
The desired product is formed when ferrous oxalate- Fe2(C2O4)3 is treated with potassium oxalate monohydrate- (COOK)2.H2O.
Chemical equation: Fe2(C2O4)3 + 3(COOK)2.H2O → 2K3[Fe(C2O4)3].3H2O
End product: K3[Fe(C2O4)3].3H2O (Potassium Ferric Oxalate)
Color of the precipitate: Green
Read More: Principle of Homogeneity
Chemicals Required
- Oxalic acid hydrate- (COOH)2.2H2O
- Ferric chloride- FeCl3
- Potassium oxalate
- Potassium hydroxide
Apparatus Required
- Beaker
- Conical flask
- Tripod stand
- Glass rod
- Wire gauze
- Filter paper
- China dish
- Funnel
Apparatus Setup
Follow the procedure given and set up your chemical apparatus with the help of the diagram given below:
Experimental Setup
Also Read: Homogeneous Equilibrium
Procedure
- Dissolve 3.5g of freshly prepared FeCl3 in 10mL of water. In another beaker dissolve 4g of KOH in 50mL of water.
- Add the KOH solution to the FeCl3 solution slowly with constant stirring. We obtain a ferric hydroxide precipitate which is brown in color. Now, filter the precipitate using a funnel and wash the precipitate with hot water.
- In another beaker take 4g of (COOH)2.2H2O and 5.5g of (COOK)2.H2O. Add 100 ml water and stir the solution until we get a clear solution of potassium oxalate.
- Now, gradually keep on adding the ferric hydroxide precipitate to the potassium oxalate solution gradually with constant stirring. Continue this step until the precipitate dissolves completely and a green color solution is formed. Filter this solution to remove any insoluble impurities if present.
- Pour the green-colored solution into a china dish. Concentrate the solution till it reaches the crystallization point. The china dish must be placed in cold water to allow the cooling of the crystals for about an hour.
- Green crystals of K3[Fe(C2O4)3].3H2O- potassium ferric oxalate are formed. Remove the crystals from the solution and wash them well with ethyl alcohol.
- Dry the crystals between the folds of filter paper and weigh them to know the yield obtained.
Green Crystal of Potassium Ferric Oxalate
Read More: Transesterification
Observations
The observations are recorded in the table given below:
| Color of the crystals | Green color |
| The shape of the crystals | Octahedral |
| Melting point | 230oC |
| Yield expected | 10 grams |
Results and Inference
The yield of Potassium ferric oxalate- K3[Fe(C2O4)3].3H2O is ___________ grams.
Precautions
- Make sure not to concentrate on the solution too much.
- To get bigger crystals, the solution must not be disturbed during the crystallization process.
- Wash the crystals with hot water so that the unwanted salts are dissolved.
Read Further: Valency of Carbon
Things to Remember
[Click Here for Sample Questions]
- Potassium ferric oxalate is a crystalline compound that is lime green in color.
- We can synthesize crystalline Potassium Ferric Oxalate (K3[Fe(C2O4)3].3H2O) by using chemicals such as oxalic acid, potassium monohydrate, and ferric chloride dihydrate.
- The process for the synthesis of Potassium Ferric Oxalate involves two steps:
- Chemical equations:
FeCl3 + 3KOH → Fe(OH)3 + 3KCl
2Fe(OH)3 + 3(COOH)2.2H2O → Fe2(C2O4)3 + 12H2O
Main product formed: Ferrous oxalate- Fe2(C2O4)3
Color of the precipitate: Yellow
- Chemical equation:
Fe2(C2O4)3 + 3(COOK)2.H2O → 2K3[Fe(C2O4)3].3H2O
End product: K3[Fe(C2O4)3].3H2O (Potassium Ferric Oxalate)
Color of the precipitate: Green
- Potassium ferric oxalate has been used in photometry, actinometry, and to create blueprints (before inkjets and laser printers came into existence).
Check Important Difference between Acid and Base
Sample Questions
Ques 1. Oxalic acid is used in excess during the synthesis of potassium ferric oxalate. Justify your statement. Why is alcohol added to the solution? [2 marks]
Ans.
- Oxalic acid is added in excess, during the synthesis of potassium ferric oxalate so that ferric hydroxide dissolves and the soluble complex is formed.
- Complex iron salt is less soluble in alcohol than water. Hence alcohol is added to the solution to precipitate out the complex salt.
Ques 2. What is crystallization? Give a few examples of a crystal. [2 marks]
Ans. Crystallisation is defined as the process in which atoms and/or molecules are organized into a structure known as a crystal. Crystallization is the process by which solid forms, where the atoms or molecules are highly organized into a structure known as a crystal.
Attributes of a crystal
The characteristics of the solid crystal will depend on factors such as temperature and air pressure. In the case of liquid crystals, the attributes depend on the time of fluid evaporation.
Formation
Crystallization occurs in two major steps: Nucleation and Crystal growth
Examples of a crystal:
- Diamond-crystal carbon
- Salt- NaCl crystals
- Quartz-silicon dioxide crystals
- Snowflakes-water ice crystals
Ques 3. What do equimolar proportions mean? [2 marks]
Ans.
- Equimolar substances have the molar ratio of their molecules as 1:1.
- In layman's language, it means having the same number of moles.
- For example, take 58.5g NaCl and 74.5g KCl and dissolve them in 1L of water. This would be an equimolar mixture of one mole each of NaCl and KCl.
Ques 4. Define seeding. [2 marks]
Ans.
- Seeding is the process of adding more crystals to a saturated solution to induce crystallization.
- This process is carried out only when the crystallization ceases in some cases.
- The crystals used for seeding are known as seed crystals. Seed crystals also help in crystal enlargement and tempering chocolates.
Ques 5. Explain the photoreduction reaction of Potassium ferric oxalate. [2 marks]
Ans.
- In solution, the salt dissociates to give the fluorescent green ferric oxalate anion, [Fe(C2O4)3]3−. The anion is stable in the dark and will be decomposed by light and high-energy electromagnetic radiations such as X-rays and gamma rays.
- The oxalate ion decomposes to give CO2 - carbon dioxide and reduces iron (III) to iron (II) atom.
- This process is also known as photolysis and this reaction finds many applications in photochemistry and actinometry.
Ques 6. Mention any 3 uses of Potassium ferric oxalate. [2 marks]
Ans. The uses of Potassium ferric oxalate are as follows:
- Photometry and actinometry
- Creating blueprints (before inkjets and laser printers came into existence)
- Chemistry education
Ques 7. Write the chemical equations involved during the synthesis of potassium ferric oxalate and the colors of precipitate formed at each step. [2 marks]
Ans.
The process for the synthesis of Potassium Ferric Oxalate involves two steps:
- A freshly prepared ferric hydroxide-Fe(OH)3 is dissolved in a solution of excess oxalic acid-FeCl3.
Chemical equations:
FeCl3 + 3KOH → Fe(OH)3 + 3KCl
2Fe(OH)3 + 3(COOH)2.2H2O → Fe2(C2O4)3 + 12H2O
Main product formed: Ferrous oxalate- Fe2(C2O4)3
Color of the precipitate: Yellow
- The desired product is formed when ferrous oxalate- Fe2(C2O4)3 is treated with potassium oxalate monohydrate- (COOK)2.H2O.
Chemical equation: Fe2(C2O4)3 + 3(COOK)2.H2O → 2K3[Fe(C2O4)3].3H2O
End product: K3[Fe(C2O4)3].3H2O (Potassium Ferric Oxalate)
Color of the precipitate: Green
Ques 8. What observations are gathered during the synthesis of potassium ferric oxalate? [2 marks]
Ans. The observations recorded during the synthesis of potassium ferric oxalate is mentioned in the table given below:
| Color of the crystals | Green color |
| The shape of the crystals | Octahedral |
| Melting point | 230oC |
| Yield expected | 10 grams |
Comments