Reaction Equation Principle And Stepwise Preparation Of Potassium Ferric Oxalate
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
Oxalic acid hydrate
Ferric chloride
Potassium oxalate
Potassium hydroxide
Beaker
Conical flask
Tripod stand
Glass rod
Wire gauze
Filter paper
China dish
Funnel
Apparatus Setup
Procedure
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.
With constant stirring, slowly add the potassium hydroxide solution to the ferric chloride solution to form a brown color ferric hydroxide precipitate.
Through the funnel, filter the ferric hydroxide precipitate and wash it with hot water.
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.
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.
Remove the insoluble impurities by filtering the solution.
Take a china dish and transfer the green-coloured solution into it and concentrate the solution till the crystallization point is reached.
In cold water, place the china dish and let it cool for an hour.
Green crystals of potassium ferric oxalate are formed. From the mother, liquor removes all the crystals.
With ethyl alcohol, wash the crystals and dry them between the folds of filter paper.
To know the yield, weigh the crystals.
Observations
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 In Laboratory
1. What is potassium ferric oxalate?
Potassium ferric oxalate is a green coordination compound with the formula K3[Fe(C2O4)3], where iron is in the +3 oxidation state. It contains the complex ion [Fe(C2O4)3]3- in which Fe3+ is octahedrally coordinated by three bidentate oxalate ligands. This compound is commonly studied in coordination chemistry and photochemical experiments due to its light-sensitive nature.
2. How do you prepare potassium ferric oxalate in the laboratory?
Potassium ferric oxalate is prepared by reacting ferric hydroxide with potassium oxalate solution followed by crystallization in the dark. The main steps are:
- Prepare freshly precipitated Fe(OH)3 by adding NaOH to FeCl3 solution.
- Filter and wash the brown Fe(OH)3 precipitate.
- Dissolve it in warm potassium oxalate solution (K2C2O4).
- Filter and concentrate the solution, then cool in the dark to obtain green crystals of K3[Fe(C2O4)3].
The reaction can be represented as:
Fe(OH)3(s) + 3K2C2O4(aq) → K3[Fe(C2O4)3](aq) + 3KOH(aq)
3. What is the balanced equation for the preparation of potassium ferric oxalate?
The balanced equation for the formation of potassium ferric oxalate from ferric hydroxide and potassium oxalate is Fe(OH)3(s) + 3K2C2O4(aq) → K3[Fe(C2O4)3](aq) + 3KOH(aq). In this reaction:
- Fe3+ forms a complex with three oxalate ions.
- Each oxalate ion (C2O42-) acts as a bidentate ligand.
- The product contains the complex ion [Fe(C2O4)3]3-.
4. Why is potassium ferric oxalate prepared in the dark?
Potassium ferric oxalate is prepared and stored in the dark because it is photosensitive and decomposes in light. On exposure to light:
- The Fe3+ ion is reduced to Fe2+.
- Oxalate ions undergo oxidation, releasing CO2.
- The green complex gradually decomposes.
Therefore, the preparation and crystallization are carried out away from direct sunlight to prevent photochemical decomposition.
5. What type of ligand is oxalate in potassium ferric oxalate?
In potassium ferric oxalate, the oxalate ion (C2O42-) acts as a bidentate ligand. A bidentate ligand:
- Has two donor atoms (two oxygen atoms in oxalate).
- Forms two coordinate bonds with the central Fe3+ ion.
- Creates a chelate ring, increasing complex stability.
Since three oxalate ions coordinate to Fe3+, the complex has octahedral geometry.
6. What is the coordination number of iron in potassium ferric oxalate?
The coordination number of iron in potassium ferric oxalate is 6. This is because:
- Each oxalate ligand is bidentate and donates two electron pairs.
- Three oxalate ligands bind to Fe3+.
- 3 × 2 donor atoms = 6 coordination sites.
Thus, the Fe3+ ion exhibits octahedral geometry in [Fe(C2O4)3]3-.
7. What are the properties of potassium ferric oxalate crystals?
Potassium ferric oxalate forms bright green, crystalline solids that are soluble in water and sensitive to light. Key properties include:
- Color: Emerald green crystals.
- Solubility: Soluble in water, forming a green solution.
- Nature: Coordination compound of Fe3+.
- Stability: Decomposes on exposure to light (photosensitive).
These properties make it useful in photochemical and analytical experiments.
8. How is ferric hydroxide prepared for the synthesis of potassium ferric oxalate?
Ferric hydroxide is prepared by adding sodium hydroxide solution to ferric chloride solution. The balanced reaction is:
FeCl3(aq) + 3NaOH(aq) → Fe(OH)3(s) + 3NaCl(aq)
- A reddish-brown precipitate of Fe(OH)3 forms.
- The precipitate is filtered and washed to remove chloride ions.
- It is then used immediately for complex formation.
9. What is the oxidation state of iron in potassium ferric oxalate?
The oxidation state of iron in potassium ferric oxalate is +3. This can be calculated as follows:
- Let oxidation state of Fe = x.
- Each oxalate ion has charge −2, and there are three: total = −6.
- Overall charge of complex ion = −3.
So, x − 6 = −3, therefore x = +3. Hence, iron exists as Fe3+ in [Fe(C2O4)3]3-.
10. What are the uses of potassium ferric oxalate in chemistry?
Potassium ferric oxalate is mainly used in photochemical studies and quantitative analysis. Important uses include:
- As a chemical actinometer to measure light intensity.
- In studying photoreduction reactions of Fe3+ to Fe2+.
- In coordination chemistry experiments to understand chelation and complex formation.
Its light sensitivity makes it especially valuable in photochemistry experiments.
