Synthesis of potassium tris(oxalato)aluminium(III) K₃[Al(C₂O₄)₃] using Al metal powder (scrap aluminium).

 Synthesis of Potassium Tris(oxalato)aluminium(III)

K₃[Al(C₂O₄)₃]

Aim

To synthesize potassium tris(oxalato)aluminium(III) complex K₃[Al(C₂O₄)₃] using aluminium metal powder (scrap aluminium) and oxalic acid.

Principle

Aluminium metal reacts with oxalic acid forming aluminium oxalate. In the presence of excess potassium oxalate, aluminium forms a stable coordination complex called potassium tris(oxalato)aluminate(III).

Oxalate ions (C₂O₄²⁻) act as bidentate ligands, coordinating with Al³⁺ to form the octahedral complex ion $[Al(C₂O₄)₃]^{3-}$. The potassium ions balance the charge to form the crystalline salt.

Reaction

1. Formation of aluminium ions

$$2Al+6H^{+}\to 2A{l}^{3+}+3H_{\mathrm{2}}$$

2. Formation of complex ion

$$A{l}^{3+}+3C_2{O}_4^{2-}\to [Al(C_2{O}_4{)}_3{]}^{3-}$$

3. Formation of complex salt

$$3K^+ + [Al(C_2O_4)_3]^{3-} \rightarrow K_3[Al(C_2O_4)_3]$$

Requirements

Chemicals

Scrap aluminium powder,Oxalic acid (H₂C₂O₄),Potassium oxalate (K₂C₂O₄),Distilled water,Ethanol

Apparatus

Beaker,Glass rod,Measuring cylinder,Funnel, Filter paper, Water bath

Procedure

1. Take about 1 g of scrap aluminium powder in a beaker.

2. Add 10–15 mL oxalic acid solution slowly and warm the mixture gently.

3. Aluminium dissolves with evolution of hydrogen gas, forming aluminium oxalate solution.

4. Add excess potassium oxalate solution to the reaction mixture while stirring.

5. Heat the solution on a water bath for 10–15 minutes until a clear solution forms.

6. Allow the solution to cool slowly.

7. Green crystals of potassium tris(oxalato)aluminium(III) separate out.

8. Filter the crystals and wash them with cold distilled water followed by ethanol.

9. Dry the crystals between filter papers.

Observation

Observation	Result
Reaction with oxalic acid	Effervescence due to hydrogen gas
Colour of solution	Light green
Colour of crystals formed	Green

Result

Potassium tris(oxalato)aluminium(III) complex K₃[Al(C₂O₄)₃] was successfully synthesized as green crystals.