Question

I need name of the final compound, and step by step equations of the reaction for the experiment below. Ethylenediamine complexes of Cobalt Procedure 1. Dissolved 1.5 g CoCl2 in 5mL water 2. While the CoCl2 6H2O is dissolving, measure out 10mL of an ethylenediamine solution. (The solution is prepared by dissolving 130mL of anhydrous ehylenediamine in one liter of water) 3.Cool the ethylenediamine solution in ice. 4.Slowly add 2.1mL 3M HCl 5.Add the CoCl2 solution to the partially neutrolized ethylenediamine and then slowly add 2mL of 30% H2O2 with stirring 6.Stir until effervescence ceases. 7.Place the mixture on a hot plate and allow to boil gently 8.When the cobalt solution is evaporated the a volume of 6 to 10mL, add and equal volume of concd. HCl and twice the amount of ethyl alcohol. 9.Cool, filter, press dry on the sintered glass funnel. Thanks.

Answer 1

The reaction sequence finally leads to a racemic mixture of tris(ethylenediamine) Co(III) chloride. We will write out the reactions step by step.

Step 1: Dissolution of CoCl₂ in water (note Co is in +2 oxidation state)

CoCl₂ + 6H₂O -------> CoCl₂.6H₂O (this is an addition compound)

Step 2: Partial neutralization of ethylene diamine by HCl acid

We know ethylene diamine is H₂NCH₂CH₂NH₂, henceforth represented as “en”.

3en + 2HCl --------> 3en.2HCl

Step 3: Reaction of Co compound from step 1 with the partially neutralized en.

CoCl₂.6H₂O + 3en.2HCl --------> [Co(en)₃]Cl₂ + 6H₂O + 2HCl

                                                 This compound is tris(ethylenediamine) Co(II) chloride with the oxidation state of Co still being +2. Now, we have a tris(ethylenediamine) complex here because the co-ordination number of Co (II) is 6 which means that it can co-ordinate to 6 ligand sites. Ethylene diamine has 2 co-ordination sites (the lone pair on both N atoms); hence three ethylene diamine ligands co-ordinate.

Step 4: Oxidation of Co (II) to Co (III).

The more stable oxidation state of Co is +3 and the oxidation here is brought about by hydrogen peroxide, H₂O₂ in acidic medium.

2 [Co(en)₃]Cl₂ +H₂O₂ + 2 HCl -------------> 2 [Co(en)₃]Cl₃ + 4 H₂O

The Co (II) has been oxidized to Co (III). The name of the compound is tris(ethylenediamine) Co(III) chloride.

The next steps, mainly evaporation and treatment with conc. HCl and ethyl alcohol followed by cooling will give crystals of tris(ethylenediamine) Co(III) chloride.