Question

4. In Part 1 of this experiment, CoCl, 6H,O reacts with ammonium chloride, ammonium hydroxide, and hydrogen peroxide to produce [Co(NH3)Cl3 and water. a) Write the balanced equation for this reaction. b) What is the purpose of adding the charcoal? c) To the test tube containing CoCl2 6H20, NH Cl, and NH OH, 3 mL of 10% H2O2 is added. Why must the H2O, be added slowly, in 1 mL portions? What is the purpose of adding the H2O2? Go d) What is the coordination number for [Co(NH)Cl2? What is the charge on the com- plex ion? Distinguish between the complex ion and the counter ion. Determine the Oxidation state of the cobalt in CoCl2 6H20 and [Co(NH3)Cl3. How many d-electrons does the cobalt have in [Co(NH3),] Cl3? 5. In Part 2 of this experiment you will synthesize [Co(NH3)sCI]Cl2 a) Write the balanced equations for the reactions to synthesize [Co(NH3)sCl] Cl2. Explain the difference in the synthesis of [Co(NH3)Cl3 and [Co(NH3)sCI]Cl2 b) What property will allow you to distinguish between [Co(NH3) ,] Cl3 and [Co(NH3), Cl] Cl2? What causes the difference? Draw the d-orbital diagrams, including the electrons, indicating the relative crystal field splitting for the two compounds. Both compounds are diamagnetic.

Answer 1

Answer :-

a) The balanced equation for the given reaction is :

2CoCl₂·6H₂O_(s) + 2NH₄Cl_(s) + 10NH₄OH_(aq) + H₂O_2(aq) = 2[Co(NH₃)₆]Cl_3(s) + 24H₂O_(l)

b) The activated charcoal/charcoal serves as a catalyst for the reaction that forms the bonds between NH₄OH or NH_3(aq) and Co. Conveniently, it also catalyzes the transformation of Co²⁺ into Co³⁺ by the H₂O₂.

c) H₂O₂ must be added slowly and in 1 ml portions, as it is unstable and decomposes to form water, oxygen gas and heat. There is liberation of oxygen gas occurring at that time, which causes effervences or bubbling and even heat is produced, so to prevent any accident to occur and to let the reaction go on smoothly, hydrogen peroxide must be added in the before said manner. The purpose of the hydrogen peroxide (H₂O₂) is to convert the cobalt from Co²⁺ to Co³⁺.

d) The total number of ligands attached to the central metal ion is called its coordination numbEr. In other words, coordination number is the number of ligands in the coordination sphere of the complex compound. Hence, the coordination number of Co in [Co(NH₃)₆]Cl₃ is 6.

A neutral coordination compound normally consists of a complex ion—a transition metal ion with attached ligands—and counter ions, anions or cations needed to produce a neutral compound.​​​​​​​ In this case  [Co(NH₃)₆]³⁺ will be the complex ion and Cl^- will be the counter ion. Complex ions are ions with a central metal ion bonded to one or more molecules or ions. A counter ion is the ion that accompanies an ionic species in order to maintain electric neutrality.

Actually [Co(NH₃)₆]Cl₃ is a neutral complex, but if only [Co(NH₃)₆]³⁺ complex ion is considered, then it has the charge 3+.

The oxidation state of Co in CoCl₂·6H₂O is +2, as the 2 Cl atoms contain charge of 1- each, so to make the addition of charges of both Co and Cl equal to 0, the oxidation state of Co will be 2+.  Let the oxidation state of Co be x

x+2(-1) = 0 ; x-2 = 0 ; x = +2

The oxidation state of Co in [Co(NH₃)₆]Cl₃ is +3.

Let the oxidation state of Co be x

As there are 6 ammonia ligands which are neutral and hence carry no charge. The chlorine ligands carry a charge of -1 each and thus they have -3 charge on them. But as the molecule in whole is a neutral the coordination sphere must carry a charge of +3. So, the oxidation state of Co is +3.   

In the complex [Co(NH₃)₆]Cl₃ the oxidation state of Co +3.

So, the electronic configuration of Co³⁺ will be [Ar]3d⁶. So it has 2 paired electrons and 4 unpaired electrons, i.e. Co has 6 d-electrons in the given complex.

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