To synthesize Pentaamminechlorocobalt(III)chloride

Aim :- 

To synthesize Pentaamminechlorocobalt (III) chloride.

Apparatus :- 

1. Flask
2. Beaker
3. Stirrer
4. Dropper
5. Steam bath
6. Filter paper
7. Buchner funnel,
8. Ice cold water
9. Measuring flask.

Chemical Requirements :- 

1. Cobalt(III)chloride
2. Ammonium chloride
3. Hydrogen peroxide
4. HCl,
5. Ammonia solution
6. Distilled water 
7. Acetone.

THEORY :- 

This is one of the oldest known complexof cobalt.

Chloropentaamminecobalt (III) chloride i sthe dichromate salt of the coordination complex [Co(NH₃)₅Cl]2+.It is purple or pink, diamagnetic and water soluble salt.The salt is prepared with a two step process starting with oxidizing a solution of cobalt chloride and ammonia.

2 CoCl2 • 6H2O + 10 NH3 + 2HCl + H2O2 → 2 [Co(NH3)5(OH2)Cl3 + 12H2O

This intermediate is then heated to induce coordination of one of the outer space chloride ligand.

[Co(NH3)5(OH2)]Cl3→[Co(NH3)5Cl]Cl2 + H2O.

In aqueous solution of chloropentaammine cobalt(III)chloride reforms aquapentaammine complex and with conc. Sulfuric acid, chloropentaammine cobalt III chloride reforms the hydrogen sulphate complex [Co(NH3)5SO3H]2+

Chemical Reactions :- 

• 2CoCl2 + 2NH4Cl + 8NH3 + H2O2 → 2[Co(NH3)5Cl] Cl2 + 2H2O
• Co2+ + NH4+ +1/2 H2O2 → [Co(NH3)5H2O]3+
• [Co(NH3)5H2O]3+ + 3Cl- →[Co(NH3)5Cl] Cl2 +H2O

PROCEDURE :- 

1. Prepare 1.8g of Cobalt III chloride in 12.5ml water.
2. In separate flask make slurry of 5.6g ammonium chloride in 5.6 ml conc. Aqueous Ammonia.
3. Add cobalt solution to slurry and stir well.
4. Add H2O2 with dropper very slowly while stirring vigorously.
5. Heat the resulting mixture on the steam bath and thick slurry is obtained.
6. If the slurry show blue tint either the evaporation is proceeding too fast or the H2O2 is added too rapidly.
7. Add HCl ( 3M, 22.5ml)and heat at 60⁰C for 10 minutes. Cool the solution to room temperature and filter in a buckner funnel with suction.
8. Wash the product with three 2ml portion of ice water and then with three 2ml portion of acetone and dry under suction
9. Transfer the product and filter paper to a solution of ammonia(2M, 68ml) warm the resulting solution on steam bath, 60⁰C.
10. After entire solid has dissolved, filter the hot solution with suction.
11. Reheat the filtrate on the steam bath with stirring. At 5 min. interval ,slowly add HCl (12ml) three times (17ml each).
12. Concentrate the solution at room temp. and filter. Wash the product with H2O (2ml) three times followed by three times washing with acetone (2ml).

PRECAUTIONS :- 

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

Practical Viva Question :- 

 •Structure of Pentaamminechlorocobalt(III) chloride

 

Geometry of Pentaamminechlorocobalt(III)

chloride