Preparation of potassium ferric oxalate

Preparation of Potassium Ferric Oxalate is a fundamental inorganic chemistry experiment commonly performed in school and college laboratories. This comprehensive guide covers all aspects of the experiment for effective learning and examination preparation.

Aim

To prepare and crystallize potassium ferric oxalate through chemical precipitation and verify its formation using qualitative analysis techniques.

Apparatus Required

Essential Laboratory Equipment:

• 250 mL beaker
• Glass rod for stirring
• Bunsen burner or heating mantle
• Tripod stand with wire gauze
• Filter funnel
• Whatman filter paper
• Conical flask (250 mL)
• Measuring cylinder (50 mL and 100 mL)
• Wash bottle containing distilled water
• Petri dish for crystallization
• Test tubes (3-4 pieces)
• Dropper
• Analytical balance
• Hot plate (optional)

Theory

Potassium ferric oxalate is a coordination compound with the chemical formula K₃[Fe(C₂O₄)₃]·3H₂O. This bright green crystalline compound is prepared through a precipitation reaction between ferric chloride and potassium oxalate.

Chemical Reaction:

FeCl₃ + 3K₂C₂O₄ → K₃[Fe(C₂O₄)₃] + 3KCl

The reaction involves the formation of a stable coordination complex where ferric ions (Fe³⁺) are coordinated with three oxalate ions (C₂O₄²⁻), creating a negatively charged complex ion [Fe(C₂O₄)₃]³⁻. This is balanced by three potassium ions (K⁺).

Key Properties:

• Bright green crystalline solid
• Soluble in cold water
• Loses crystallization water upon heating
• Exhibits characteristic iron and oxalate ion tests

Procedure

Step-by-Step Experimental Method:

1. Solution Preparation:

   • Prepare 50 mL of 0.2M ferric chloride solution in a 250 mL beaker
   • Prepare 50 mL of 0.6M potassium oxalate solution in another 250 mL beaker
   • Heat both solutions gently to about 60-70°C

2. Precipitation Process:

   • Slowly add the ferric chloride solution to the potassium oxalate solution with continuous stirring
   • Maintain the temperature during addition to ensure complete reaction
   • Avoid rapid addition to prevent side reactions

3. Crystallization:

   • Allow the precipitate to settle for 10-15 minutes
   • Filter the precipitate using filter paper and funnel
   • Wash the precipitate with small amounts of ice-cold distilled water
   • Transfer the wet crystals to a Petri dish
   • Allow slow evaporation at room temperature for crystal growth

4. Drying:

   • Dry the crystals between sheets of filter paper
   • Store in a desiccator to prevent moisture absorption

Observation Table

Qualitative Analysis Tests:

Result

The experiment successfully demonstrates the preparation of potassium ferric oxalate trihydrate (K₃[Fe(C₂O₄)₃]·3H₂O) as bright green crystalline solid. The qualitative analysis confirms the presence of all constituent ions:

• Iron (Fe³⁺) - Confirmed by blue precipitate with potassium ferrocyanide
• Oxalate (C₂O₄²⁻) - Confirmed by white precipitate with calcium chloride
• Potassium (K⁺) - Confirmed by lilac flame in flame test

The theoretical yield calculation shows good agreement with experimental results, indicating proper experimental technique and high purity of the final product.

Precautions

Laboratory Safety Measures:

⚠️ Chemical Handling:

• Handle ferric chloride with care as it can cause skin irritation
• Wear safety goggles and laboratory gloves throughout the experiment
• Avoid inhalation of chemical powders

???? Experimental Technique:

• Maintain proper temperature during mixing to prevent decomposition
• Add solutions slowly with constant stirring for uniform precipitation
• Use ice-cold water for washing to minimize product loss

????️ Heating Safety:

• Heat solutions gently to avoid boiling
• Use tripod stand and wire gauze for even heat distribution
• Do not overheat the final product

???? General Guidelines:

• Clean all apparatus thoroughly before use
• Use distilled water for all washing purposes
• Store the final product in a dry environment to prevent moisture absorption

Viva Voce Questions and Answers

Q1: What is the chemical formula of potassium ferric oxalate? A: K₃[Fe(C₂O₄)₃]·3H₂O

Q2: Why is heating required during the preparation? A: Heating increases the solubility of reactants and ensures complete reaction formation of the coordination complex.

Q3: What type of compound is potassium ferric oxalate? A: It is a coordination compound (complex salt) where Fe³⁺ is the central metal ion coordinated with oxalate ligands.

Q4: How can you test for the presence of iron in the compound? A: Add potassium ferrocyanide solution - formation of deep blue precipitate confirms Fe³⁺ ions.

Q5: What is the significance of slow cooling in crystallization? A: Slow cooling allows proper crystal growth, resulting in well-formed, pure crystals with better yield.

Q6: Why should ice-cold water be used for washing the crystals? A: Cold water minimizes the solubility loss of the product and prevents dissolution of crystals during washing.

Q7: What precautions should be taken while handling ferric chloride? A: Ferric chloride should be handled carefully as it's corrosive; use protective gloves and avoid contact with skin or eyes.

Conclusion

The preparation of potassium ferric oxalate experiment provides valuable insights into coordination chemistry and crystallization techniques. The successful synthesis of bright green crystals confirms proper experimental execution and understanding of complex salt formation. This experiment enhances practical skills in inorganic chemistry synthesis and qualitative analysis.