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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+ + 4NH3(aq) +CO32- _ 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

Substance

Amount

Co(NO3)2

3.614 g

NH4NO3

2.585 g

Ammonium Hydroxide

40 ml

H2O

10 ml

Peroxide

24.5 ml

Nitric Acid

5 ml

Nitric Acid

30 ml

Ethanol

125 ml

Dry Participant

1.7222 g

Ammonium Hydroxide

6.67 ml

H2O

33.33 ml

Ethanol

2.5 ml

Beaker weight

30.2199 g

Beaker & Dry Participant weight

31.5379 g

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.    

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