Inorganic Complex Synthesis: Preparation of
Chloropentammine Cobalt(III) Chloride
In this lab, we will prepare the cobalt(III) complex chloropentammine cobalt(III) chloride.
This requires a redox reaction since we begin with cobalt(II) that is oxidized via hydrogen
peroxide to form the cobalt(III) specie. The final product is:
(2+)
Cl
H3N
Co
H3N
NH3
NH3
2 Cl
NH3
The product forms according to this equation:
2 CoCl2 • 6H2O + 4 NH4Cl + 8 NH3 + H2O2  2 [Co(NH3)5Cl)]Cl2 + 14 H2O
PROCEDURE
In a 125-mL Erlenmeyer flask, dissolve 15 mmol ammonium chloride in 12 mL of
concentrated ammonium hydroxide (CAUTION! Do not breathe vapor. Do not come into
contact. Work in hood!). To this solution add 7 mmol cobalt (II) chloride hexahydrate
solid. Stir with a magnetic stirbar until all of the salt dissolves and a brown slurry is
formed.
Pipet 1.5 mL of 30% hydrogen peroxide solution (CAUTION! Causes severe chemical
burns) into a small test tube. While continuing to stir, add the hydrogen peroxide with a
dropper, adding 1-2 drops every 15-30 seconds. Wait for the bubbling to subside after all
of the peroxide is added. Obtain 7 mL of conc. hydrochloric acid (CAUTION!). Using a
disposable dropper, add ~1 mL portions while maintaining continuous stirring; wait until
the bumping subsides before adding subsequent portions.
Continue to stir and set the hotplate on a low setting. Using the hotplate, maintain a
temperature of 80-85°C for 30 minutes. Next, allow the mixture to cool to room
temperature. While waiting, cool 15 mL water and 10mL of 95% ethanol in an ice water
bath. Once cooled, filter the product by vacuum filtration. Wash the product on the filter
two times with about 5 mL of ice cold water, then two times with ice cold ethanol, then
three times with acetone.
Set aside to dry and obtain mass of product.
Calculate percentage yield, atom economy and e-factor.