Question

(i) Give a chemical test to show that \( [Co(NH_3)_5SO_4]Cl \) and \( [Co(NH_3)_5Cl]SO_4 \) are ionisation isomers.
(ii) What is meant by the 'Chelate effect'? Give an example.

Hint:

Precipitation tests only work for ions located outside the coordination sphere (brackets). Ions inside the brackets are not released in water.

Answer 1

(i) Give a chemical test to show that \( [Co(NH_3)_5SO_4]Cl \) and \( [Co(NH_3)_5Cl]SO_4 \) are ionisation isomers.

Solution:
To show that \( [Co(NH_3)_5SO_4]Cl \) and \( [Co(NH_3)_5Cl]SO_4 \) are ionisation isomers, we can perform a chemical test involving the ions present in the compounds: - \( [Co(NH_3)_5SO_4]Cl \) contains chloride ions (Cl⁻) and sulfate ions (SO₄²⁻), where chloride is the counter ion. - \( [Co(NH_3)_5Cl]SO_4 \) contains sulfate ions (SO₄²⁻) and chloride ions (Cl⁻), where sulfate is the counter ion. A test can be performed by adding an excess of silver nitrate (AgNO₃) to both solutions. - In the case of \( [Co(NH_3)_5SO_4]Cl \), AgNO₃ will react with the chloride ions (Cl⁻) to form a white precipitate of silver chloride (AgCl). - In the case of \( [Co(NH_3)_5Cl]SO_4 \), AgNO₃ will react with the sulfate ions (SO₄²⁻) to form a white precipitate of silver sulfate (Ag₂SO₄). The formation of different precipitates indicates that the two compounds are ionisation isomers.

(ii) What is meant by the 'Chelate effect'? Give an example.

Solution:
The 'Chelate effect' refers to the enhanced stability of a coordination complex when a multidentate ligand (a ligand that can form multiple bonds to a metal ion) binds to the metal ion, compared to when a monodentate ligand (a ligand that can form only one bond) is used. The chelate effect arises due to the formation of a ring structure that includes the metal ion, which results in a more stable complex due to the entropic and enthalpic factors associated with ring formation.
An example of the chelate effect is the complex formed by ethylenediamine (en) with a metal ion. Ethylenediamine is a bidentate ligand, meaning it can form two bonds to the metal center, creating a five-membered ring. The resulting complex is more stable compared to the complex formed with two separate monodentate ligands like ammonia (NH₃).