An infrared spectrum is a plot of the absorption intensities of different wavelengths of infrared light. The IR spectrum of [Co(NH3)5Cl]Cl2 consists of absorptions primarily attributed to the NH3 groups.
Results
Table 1: Result of synthesis of [Co(NH3)5Cl]Cl2
Table 2: Results of Electroconductivity
- This data was obtained from other groups.
Table 3: Results of IR spectrum of [Co(NH3)5Cl]Cl2
Simple calculation
- Theoretical mass
Moles of [Co(NH3)5Cl]Cl2
= mass of Co(NH3)4CO3]NO3 x 1 / (MW of Co(NH3)4CO3]NO3) x MW of [Co(NH3)5Cl]Cl2
= 2.5g x (1/ 249.0695 g/mol ) x 250.4956g/mol
= 2.51g
- Percentage yield
= Actual mass / theoretical mass x 100
= 2.29g / 2.51g x 100
= 91.23 %
-
Molar conductivity(Λm)
Λ =
= 1000 x 0.41 mΩ-1 x 0.001M x 1/1000
=410 Λm
Discussion
The synthesis of [Co(NH3)5Cl]Cl2 was began with 2.5g of the [Co(NH3)4CO3]NO3. The reaction produced 2.29g of [Co(NH3)5Cl]Cl2 which was 91.23% of the expected product. This was a much more productive reaction, in that there was only 8.77% error. The product was an orange color and it was similar look and texture to the [Co(NH3)4CO3]NO3.
[Co(NH3)4CO3]1+ from other group made was used to synthesize [Co(NH3)5Cl]Cl2. In this particular case, the chlorine ion was a monodentate ligand because it only had one binding site. First, ligand exchange occured by introduction of hydrochloric acid to the ion.
[Co(NH3)4CO3]1+ + 2HCl → [Co(NH3)4(OH2)Cl]2+ + CO2 + Cl1-
Ammonia was a better ligand than Cl-, so when it was present, it replaced the Cl in the complex to give:1
[Co(NH3)4CO3]1+ + NH3(aq) → [Co(NH3)5(OH2)]3+ + Cl1-
Again, due to the greater electronegativity of the NH3 than that of Cl-, the Cl- associated with the cobalt is replaced by the ammonia.1
Next, HCl was added back into the solution of [Co(NH3)5(OH2)]3+ to give the desired product.
[Co(NH3)5(OH2)]3+ + 3HCl → [Co(NH3)5Cl]Cl2 + H20 + 3H+
However, there was percentage error of 8.77%. One of the factors that may have contributed to the percent error is the short evaporation stage. The solution may not have been given enough time to evaporate any impurities. Also, during heating [Co(NH3)5(OH2)]3+ this compound may be boiled and decomposed. The other factor is measurement errors. Although a good level of confidence can be felt about whether or not the right amounts were added, there is always room for error. A simple miscalculation or slight deviation in a measurement could have thrown off the remainder of the synthesis. Also, filtering system may cause the source of error. The crystal product is quit soluble in water that its ions can be easily separated. This was reason that iced cold water was used to wash. In the filter, some of the crystals could have dissolved and fallen through, which could result in a error of yield.
Once the product had been obtained, analysis could be accomplished. The identity of unknown compounds could be revealed through determination of that compound’s electroconductivity. By studying the electrical conductance of a particular substance, it was possible to relate that to the number of ions in that substance. Electroconductivies could be found and analyzed for the product obtained. This part had been done by other gourps due to lacking of experimental time. By simply looking at the proposed structure and deciding how many ions it had, then comparing that number to the actual number of ions the synthesized compound contained, [Co(NH3)5Cl]Cl2] should have 3 ions by looking at the charges. However, it was determined that it did not have 3 ions since molar conductance was not in range of 235-273. The calculated range of molar conductance was close to about 400 and this could be said to be close to 4 ions. This may be caused due to impurities. The product may not isolated and purified perfectly and residues may be remained in the product that was not washed properly.
An IR for [Co(NH3)5Cl]Cl2 was run in ATR accessory. The results showed that there were peaks at 3284.43, 1612.66, 1300, and 849.60 cm-1.Usually, it is useful to compare infrared spectrum of other coordination compound to compare their properties. However, there was no other else compound tested to compare with [Co(NH3)5Cl]Cl2. But structurally, this compound contained no carbonyl groups. The peaks at four frequencies were ammonia groups. Other stretching modes (e.g. Co-N, Co-Cl) were, also measurable, but might occur at a lower frequency than could be observed in a typical infrared spectrophotometer.2
In general, this experiment ran very smoothly and achieved its purpose of providing detailed information regarding the properties and synthesis processes of a transition metal coordination compound. To improve the results of percentage yield and perhaps to improve the results in areas of characterization will be needed in future experiment.
Questions
8.
[Co(NH3)4CO3]NO3 is the trigonal bipyramid and [Co(NH3)5CO3]NO3 is the octahedral complex compound. Even [Co(NH3)5CO3]NO3 has one more atom of NH3, they both have same charge +2, because NH3 is neutral. An ammine ligand bound to a metal ion is markedly more acidic. Hence, [Co(NH3)5CO3]NO3 is more acidic since it has one more ammonia atom. It can be distinguished by litmus paper or pH test to identify which compound is more acidic assuming mass of reactant are same.
9.
The cell constant,k will be changed if the electrodes in a conductivity cell are bent or moved. In theory, a conductivity measuring cell is formed by two 1-cm square surfaces spaced 1-cm apart. The cell constant is a function of the electrode areas, the distance between the electrodes and the electrical field pattern between the electrodes. If the electrodes are moved or bent, electrode areas will be changed and therefore cell constant will be changed.
Reference
- Gregory S.G; Thomas B.R; Robert J.A, synthesis and technique in ingorganic chemistry, third edition
- James E. House, Inorganic chemistry, 2008.
Gregory S.G; Thomas B.R; Robert J.A, synthesis and technique in inorganic chemistry, third edition.
James E. House, Inorganic chemistry, 2008.