Exam (elaborations)

Coordination Complexes- Cobalt (III) Ammine Complexes - lab Reort University of Calgary CHEM 333

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CHEM 333

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CHEM 333

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coordination complexes cobalt iii ammine complexes anusha ambaselkar lab b05 a 1 january 28
2021 abstract in this experiment
tetraamminecarbonatocobalt iii nitrate 1114g
326 and pentaamm

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Coordination Complexes- Cobalt (III) Ammine Complexes
Anusha Ambaselkar Lab B05 A-1
January 28, 2021

Abstract:

In this experiment, tetraamminecarbonatocobalt (III) nitrate (1.114g, 32.6%) and

pentaamminechlorocobalt(III) chloride (0.454g, 89.0%) was synthesized. Ammonium carbonate

solution and cobalt (II) hexahydrate solution was mixed, evaporated and filtrated to prepare the

intermediate of tetraamminecarbonatocobalt (III) nitrate. A sample of this intermediate was used

to synthesize pentaamminechlorocobalt(III) chloride by replacing the carbonate ligand with a

chlorine ligand through evaporation and filtration. Conductance measurements were obtained of

the two products as well as three stock solutions of KCl, MgCl2 and Na3PO4ᐧ 12 H2O. These

were then converted to molar conductivities using a formula in order to assign the number of

ions present in the ionic species. Tetraamminecarbonatocobalt (III) nitrate (116.96(Sᐧ cm2/mol),

2 ions) and pentaamminechlorocobalt(III) chloride (235.23(Sᐧ cm2/mol), 3 ions).

Introduction:

Conductance of a coordination complex with a known concentration can be used to

determine the number of ions in solution. The conductivity determined experimentally however

reflects all ions that are mobile and carry current as well as dependent on concentration.[1] This

concentration dependence prohibits the comparison between different solutions thus molar

conductivity (Am) is used between known ionic species that consist of different numbers of ions.

The Am ranges that correspond with the number of ions help determine if the experimental

product has the same number of ions as the known ionic species.

The purpose of this experiment was to synthesize two cobalt (III) coordination

complexes. In part A of the experiment, tetraamminecarbonatocobalt (III) nitrate was made and

in part B of the experiment pentaamminechlorocobalt(III) Chloride was made. After their

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, synthesis, the conductance of each cobalt complex was measured using a conductivity meter.

This conductance was then converted into molar conductance (Am) in order to compare with

KCl, MgCl2, and Na3PO4ᐧ 12 H2O stock solutions to prove the number of ions of the

experimental products.

Product Reactions:

Tetraamminecarbonatocobalt (III) nitrate [Co(NH3)4CO3]NO3

10 Co(NO3)2 + 26NH3 + 10(NH4)2CO3 + H2O2 → 8 NH4NO3OH + 10 [Co(NH3)4CO3]NO3

Pentaamminechlorocobalt(III) Chloride [Co(NH3)5Cl]Cl2

[Co(NH3)4CO3]++ 2HCl → [Co(NH3)4(OH2)Cl]2++ CO2 + Cl-
[Co(NH3)4(OH2)Cl]2+ + NH3 → [Co(NH3)5(OH2)]3+ + Cl-
[Co(NH3)5(OH2)]3+ + 3HCl → [Co(NH3)5Cl]Cl2 + H2O + 3H+

Methods:

Part A: Preparation of Tetraamminecarbonatocobalt(III) Nitrate

Ammonium carbonate (36.4 mmol, 3.505g) was dissolved in water (10.0mL) along with

concentrated aqueous NH3 (NH4OH) to form solution A.[1] Cobalt (II) Nitrate Hexahydrate (8.6

mmol, 2.510g) was dissolved in water to form solution B. Solution A and solution B was mixed

resulting in a solution that was a deep purple opaque color. 30% Hydrogen Peroxide (2.0mL)

was slowly added dropwise into the solution while stirring continuously. Some bubbles occurred

during this process. This solution was poured into an evaporating dish to be heated (70℃) on a

hot plate for approximately 25 minutes in order to concentrate to less than half the original

amount. During the evaporation process, ammonium carbonate (1g, 10.4mmol) was added in

small portions to the evaporating dish. Using vacuum filtration, filter this solution and cool the

filtrate using an ice water bath. After 7 minutes of crystallization, the solution was filtered again

through vacuum filtration resulting in reddish-pink precipitate left in the funnel. After washing

with water (2.1mL) and cold ethanol (3 x 5mL), a bright fuschia pink solid powder was isolated

(1.114g, 32.6%

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