Transcribed Image Text:1) Give a balanced equation for the reaction.
2) What are the roles of: (i) water solvent; (ii) activated carbon; (iii) H₂O2; (iv) NH4Cl;
(v) the conc. HCI in the final crystallization step.
3) Give the d electron count and oxidation state of the metal for the final product.
Transcribed Image Text:Expt. 2. Synthesis of Hexaamminecobalt(III) Chloride
In this experiment, you will synthesize a coordination complex, [Co(NH3)6]³+.
The target product is a traditional Werner complex with a central metal ion and an
inner sphere of coordinated ligands. This complex ion will be isolated as a salt,
with outer-sphere counterions balancing the charge of the complex. Unlike many
organic reactions that require organic solvents, many classic inorganic syntheses
of coordination compounds are readily performed in water.
The preparation of hexaammine cobalt(III) salts is carried out most
conveniently from cobalt(II) chloride hexahydrate, CoCl2-6H₂O, which is both
stable and inexpensive. Hexaamminecobalt(III) salts can be prepared using
aqueous ammonia as a source of NH3, activated charcoal as catalyst and an
oxidant such as H₂O2, 12, O2, KMnO4, or PbO2.¹ A high concentration of ammonium
salt stabilizes the hexaamminecobalt(III) ion where the charcoal catalyzes the
ligand exchange.
Add 4.8 g of CoCl2 6H₂O and 3.2 g of NH4CI to 20 mL of water in a 125 mL
or 250 mL Erlenmeyer flask with a side arm (filtering flask). Gently agitate the flask
until all of the solids are dissolved. Then add 0.5 g of fresh activated decolorizing
carbon (charcoal) and 10 mL concentrated ammonia in the fumehood. Swirl the
flask for several minutes.
Next, add 5 mL of 30% H₂O2 dropwise while swirling/stirring. The addition
needs to be done dropwise using a Pasteur pipette - the reaction is vigorous
and will bubble over if you add all the H₂O2 at once. The reaction will get hot
during the addition. Continue swirling the mixture for 10 min; you may continue to
see bubbles. Then cool the mixture in an ice bath for 10 min. Collect the solids
by suction filtration using a Buchner funnel fitted with two pieces of filter paper.
Transfer the damp filter cake into a 250 mL beaker.
Prepare a solution of 6 mL concentrated HCI in 80 mL of water and add it
to the beaker containing the filter cake. Heat the mixture to a boil for 5 min and
then suction filter while still hot. Slowly add 10 mL of concentrated HCI to the
filtrate in the filter flask, swirl to mix, and then place the flask in an ice bath. Cool
the mixture on ice for 30 min. Collect the orange crystalline solid on filter paper by
suction filtration using a Buchner funnel. Rinse the crystals with ethanol and then
acetone. Allow the product to dry by passing air through it (i.e. leave the vacuum
on while the solid is in the Buchner funnel on the filter flask) for approximately
5 min. Weigh the solid to determine your yield and transfer it to a glass vial for
storage.
UV-Vis spectrum: dissolve a known amount of your product (50 to 75 mg
but record the exact mass used) in precisely 25 mL deionized water. Obtain the
spectrum (plastic cuvettes are ok to use) and calculate the extinction coefficient of
the complex and percent yield.
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![Expt. 2. Synthesis of Hexaamminecobalt(III) Chloride
In this experiment, you will synthesize a coordination complex, [Co(NH3)6]³+.
The target product is a traditional Werner complex with a central metal ion and an
inner sphere of coordinated ligands. This complex ion will be isolated as a salt,
with outer-sphere counterions balancing the charge of the complex. Unlike many
organic reactions that require organic solvents, many classic inorganic syntheses
of coordination compounds are readily performed in water.
The preparation of hexaammine cobalt(III) salts is carried out most
conveniently from cobalt(II) chloride hexahydrate, CoCl2-6H₂O, which is both
stable and inexpensive. Hexaamminecobalt(III) salts can be prepared using
aqueous ammonia as a source of NH3, activated charcoal as catalyst and an
oxidant such as H₂O2, 12, O2, KMnO4, or PbO2.¹ A high concentration of ammonium
salt stabilizes the hexaamminecobalt(III) ion where the charcoal catalyzes the
ligand exchange.
Add 4.8 g of CoCl2 6H₂O and 3.2 g of NH4CI to 20 mL of water in a 125 mL
or 250 mL Erlenmeyer flask with a side arm (filtering flask). Gently agitate the flask
until all of the solids are dissolved. Then add 0.5 g of fresh activated decolorizing
carbon (charcoal) and 10 mL concentrated ammonia in the fumehood. Swirl the
flask for several minutes.
Next, add 5 mL of 30% H₂O2 dropwise while swirling/stirring. The addition
needs to be done dropwise using a Pasteur pipette - the reaction is vigorous
and will bubble over if you add all the H₂O2 at once. The reaction will get hot
during the addition. Continue swirling the mixture for 10 min; you may continue to
see bubbles. Then cool the mixture in an ice bath for 10 min. Collect the solids
by suction filtration using a Buchner funnel fitted with two pieces of filter paper.
Transfer the damp filter cake into a 250 mL beaker.
Prepare a solution of 6 mL concentrated HCI in 80 mL of water and add it
to the beaker containing the filter cake. Heat the mixture to a boil for 5 min and
then suction filter while still hot. Slowly add 10 mL of concentrated HCI to the
filtrate in the filter flask, swirl to mix, and then place the flask in an ice bath. Cool
the mixture on ice for 30 min. Collect the orange crystalline solid on filter paper by
suction filtration using a Buchner funnel. Rinse the crystals with ethanol and then
acetone. Allow the product to dry by passing air through it (i.e. leave the vacuum
on while the solid is in the Buchner funnel on the filter flask) for approximately
5 min. Weigh the solid to determine your yield and transfer it to a glass vial for
storage.
UV-Vis spectrum: dissolve a known amount of your product (50 to 75 mg
but record the exact mass used) in precisely 25 mL deionized water. Obtain the
spectrum (plastic cuvettes are ok to use) and calculate the extinction coefficient of
the complex and percent yield.](https://content.bartleby.com/qna-images/question/d6957468-6fb1-4659-9083-987b06676d6d/9e90d8c9-3009-4b20-a167-96ae4662d773/hsfwqw6_processed.png)
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