PREPARATION AND CHARACTERISATION OF POTASSIUM TRIS OXALATO CHROMATE(III) TRIHYDRATE

Aim :- 

PREPARATION AND CHARACTERISATION OF POTASSIUM TRIS OXALATO CHROMATE(III) TRIHYDRATE

Apparatus :- 

1. Conical flask
2. Watchman filter
3. Oxalic acid
4. Potassium dichromate
5. Potassium oxalate monohydrate
6. Ethanol
7. Ice water bath.

Chemical formula: - 

K3[Cr(C2O4)3].3H2O

• Reduction : -   14H++ Cr2O72-+6C2O42-+6e-→ 2Cr(C2O4)32-+7H2O
• Oxidation: 3C2O4  → 6CO2+6e-
• Overall Equation: K2Cr2O7+7H2C2O4+2 K2C2O4 → K3[Cr(C2O4)3]+6CO2+7H2O

Procedure:- 

1. Mix 5g of oxalic acid in 10mL of water with potassium dichromate in a 25mL conical flask.
2. A blue-black or dark blue mixture was formed and spontaneously warm up almost to boiling.
3. Bubbles formation would be observed.
4. After about 15 minutes, dissolve 2.10g of potassium oxalate monohydrate in the mixture.
5. Heat the mixture for approx. 15 minutes.
6. Let it cool down to room temperature.
7. Now add 10mL of 95% ethanol and cool the mixture using ice bath for about 15-30 minutes.
8. A dark green colored precipitate will be formed at the bottom of the conical flask.
9. Now collect the precipitate using Whatman filter in a suction pump.
10. Let the precipitates dry by keeping in oven.
11. Now calculate the theoretical and percentage yield of potassium tris(oxalato)chromate(III) trihydrate. 

Precaution :- 

1. Use chemical carefully 
2. Handle the chemicals and reagents carefully.
3. Safety glasses and gloves must be worn while performing the experiment.
4. Weigh the chemicals accurately.
5. Use tongs while holding the hot glasswares.
6. Always double check the name of the reagent you are using.
7. Always label all test tubes and other containers with contents.

UV Visible Spectra of Potassium tris oxalato m chromate(III) trihydrate :- 

• Oxalato is a bidentate ligand and in this compound shows two absorption maxima at 
• 415 nm(4A2g 4T1g) and 570 nm (4A2g 4T2g) in methyl alcohol as a solvent.
• The UV Visible spectrophotometer is used to record the spectra. 
• The first band is little sharper and intense at 415 nm and the second band at 570 nm broad and less intense than first.
• The powder form of the compound show slightly different absorption peaks, though their spectra show similar pattern to that in solvent.