Question

1. It would also be possible to separate Co²⁺ and Ni²⁺ on a cation exchange column as opposed to the anion exchange column employed in this experiment. What is the main advantage of the procedure we used (anion exchange column)?

2. In aqueous solution, Co2+ forms the complex Co(H20)62+ (λmax = 513 nm, e = 4.8 M-1cm-1). Why did we complex the Co2+ solution with thiocyanate instead of simply taking absorbance measurements of the aqueous solution?

3. Why is it necessary to re-equilibrate the ion exchange column with 9M HCl between seperation runs? What would happen if this step were omitted?

Answer 1

SOLUTION:

1.

In this experiment, principles of ion-exchange will be used to separate cobalt and nickel ions (Co2+ and Ni2+) based on formation of anionic complexes with chloride. Many metal ions form anionic chloro-complexes in concentrated hydrochloric acid solutions. These chloro-complexes can be exchanged with mobile anions originally associated with the immobile cationic groups of an ion-exchange resin. The retention of the anionic chloro-complexes on the ion-exchange column depends on the nature of the complexes. Metal ions that do not form anionic chloro-complexes will be repelled by the cationic groups on the resin and will therefore elute from the column.

2.