Lab Report Writing

Cobalt nitrate [Co(NO₃)₂] is deliquescent, that is it tends to absorb atmospheric water vapor. The nitrate attain the formula Co(NO₃)₂.6H₂O upon exposure to atmosphere. The Co(II) complex has a rapid reaction by ligand reaction as in the reaction below:

Co(OH₂)₆²⁺ + 4NH_3(aq) +CO₃^2- _ Co(NH₃)₄CO₃ +6H₂O

The product formed is tetraamminecarbonatocobalt (II) which is oxidized by H₂O₂ to form [Co(NH₃)₄CO₃]⁺  

The compound [Co(NH₃)₄CO₃]NO₃  is prepared by the H₂O₂ oxidation of [Co(H₂O)₆](NO₃)₂ in the presence of NH₃ and (NH₄)₂CO₃.

Co(NO₃)₂ + 4NH₃(aq) + (NH₄)₂CO₃ + ½ H₂O₂ → [Co(NH₃)₄CO₃]NO₃ + 2NH₄⁺ + NO₃^- + OH^- 

The carbonate ion is then expelled as carbon dioxide by the addition of excess acid, resulting in the initial formation of [Co(NH₃)₄(H₂O)₂]³⁺. The excess acid is then neutralized with NH₃, resulting in the formation of [Co(NH₃)₅(H₂O)]³⁺. HCl is added to form [Co(NH₃)₅Cl]Cl₂.

Representation of the process.

[Co(NH₃)₄CO₃]NO₃ + 2HCl → [Co(NH₃)₄(H₂O)₂]³⁺ + CO₂(g) + 2Cl^- + NO₃^- + H₂O

[Co(NH₃)₄(H₂O)₂]³⁺ + NH₃ → [Co(NH₃)₅(H₂O)]³⁺ + H₂O

[Co(NH₃)₅(H₂O)]³⁺ + HCl → [Co(NH₃)₅Cl]Cl₂ + H₃O⁺

Procedure

Dissolve 20 g of peroxide in 10 ml of water and add 5 ml concentrated

aqueous NH3. Dissolve 15 g of cobalt(II) nitrate hexahydrate in 30 ml of water. Mix NH₃ with the solution formed from mixture of cobalt (II) nitrate hexahydrate and water, and add 8.0 ml of 30% hydrogen peroxide solution and stir continuously. Pour the resulting solution to an evaporating dish and make a concentration of about 90 ml on a hot plate. Add in small portions, of 5 g of ammonium carbonate during the evaporation process. Sieve the hot solution and cool it by a water bath. Crystallization takes place and when complete, the crystals are filtered and washed with 3 ml of water then with 10 ml of ethanol in a number up to three times.

Data collected table

Calculations

Calculation of weight required by the formula below

Weight = A/C where;

A= Absorbance measured by experiment

C= molar concentration which is calculated from the measured value of A

Co (OH2)62+ + 4NH3 (aq) + CO32- → Co (NH3)4CO3 + 6H2O

[Co (H2O) 6](NO3)2(s) + 3NH3 (aq) + (NH4)2CO3(s) + H2O2 (l) 4H+4e- → [Co(NH3)4CO3]NO3(s) + NH4NO3(g) + 8H2O(g) [balanced reaction equation]

The complex mass yielded=

Mass yield = 6.15 g of [Co (NH3)4CO3]NO3(s)

Therefore, the yield=

Mass of cobalt = (15/291.0352)(1 mole of cobalt/ 1 mole of hexaquacobalt)(58.933 cobalt/1 mol cobalt) = 1.762 g

Percentage yield = (1.762/3.037) 100

                         =58.0178%  

Discussion

In the experiment, a larger molecule is synthesized from smaller ones. There are two electron bonds in the coordination compound, both electrons coming from the ligand. The metal ion acts as an electron deficient species that can use its empty orbital from the bond. The ammonium and chloride ligand uses the pairs of electrons and form bonds with cobalt cation. The cobalt ion attains a 3+ charge, each of the chloride ions has 1- charge and the ammonium ligand remains neutral. That is, [Co(NH₃)₆] attains a net 3+ charge and [Co(NH₃)₅Cl] has a 2- charge. The cation complexes crystallize from the solution as chloride salt.

Conclusion

Cobalt (II) chloride is hygroscopic thus available as a hydrate CoCl₂.6H₂O. It does not form a chemical bond with water, but results by water being incorporated into the crystal structure of CoCl₂ in solid form.