1. The document describes the preparation of the complex potassium trioxalatoaluminate(III) from aluminum metal, oxalic acid, and potassium hydroxide. 2. Aluminum metal reacts with oxalic acid in an alkaline solution to form the complex ion where oxalate ligands bind to aluminum in a six-coordinate structure. 3. The procedure involves dissolving aluminum in potassium hydroxide, adding oxalic acid, crystallizing the product, washing with water and ethanol, and collecting the white crystalline potassium trioxalatoaluminate(III) complex.

1. SHREE MALLIKARJUN COLLEGE TYBSC
SAFETY: Refer to MSDS of Al metal, oxalic acid, potassium hydroxide, ethanol
-Dr. Mithil S. Fal Desai
Aim: Preparation of potassium trioxalatoaluminate(III).
Chemicals: Al metal, oxalic acid, potassium hydroxide, ethanol
Apparatus: Beakers, conical flask, funnel, glass rod,
Theory:
The complex potassium tris(oxalate)aluminate(III) trihydrate, K3[Al(C2O4)3].3H2O, is a white
crystalline salt. It is soluble in water and insoluble in alcohol. Al metal is amphoteric thus it
dissolves in alkali and acid, liberating hydrogen. The oxalic acid act as a bidentate ligand and
forms a six coordinated complex with Al.
Reaction:
2Al + 6KOH + 6H2C2O4 → 2K3[Al(C2O4)3].3H2O + 3H2
Procedure: 1. Weigh approximately 0.5 g of Al into a 250 mL beaker.
2. Add 20 mL of 10% w/v KOH solution and heat to dissolve. (Careful!)
Do not allow the solution to dry up.
3. Filter the solution.
4. Dissolve 8.0 g of oxalic acid in a minimum quantity of water.
5. Add dropwise oxalic acid solution to [Al(OH)4]-
(aq) solution.
6. Reduce the volume of the solution (about 25 - 30 mL) and allow the product to crystalize on an
ice bath.
7. Filter and wash the crystallized product with small quantities of cold distilled water and ethanol.
(Caution: compound is soluble in water)
8. Dry the crystallized product and report the percentage yield.
Questions
1. Draw the structure of the trioxalatoaluminate(III) ion.
2. How you will check the presence of oxalate in the complex?
3. How you will check the presence of potassium in the complex?
4. Can you use Al2(SO4)3 instead of Al metal to prepare the complex?
5. Why we use the KOH solution?
6. Why we heat the solution till boiling after adding the aluminum?
7. Why there is a need to wash the complex formed with water?