Ligand exchange and the chelate effectEdexcel International A Level Chemistry: Mind map

Exam questions on Ligand exchange and the chelate effect

1. A student adds dilute aqueous ammonia, first a few drops and then in excess, to a pale blue aqueous solution of copper(II) sulfate. The solution contains the hexaaquacopper(II) ion, [Cu(H₂O)₆]²⁺.
   Write an equation for the formation of the pale blue precipitate and state the role of ammonia in this reaction.2 marks
2. A student dissolves cobalt(II) chloride in water to give a pink solution containing [Co(H₂O)₆]²⁺. She then adds concentrated hydrochloric acid, and the solution turns blue. When water is added to the blue solution, the pink colour returns.
   Explain why the colour of the blue solution changes to pink when water is added.2 marks
3. A student studies two reactions of aqueous copper(II) sulfate. In the first, concentrated hydrochloric acid is added to the solution. In the second, she prepares crystals of tetraamminecopper(II) sulfate monohydrate, [Cu(NH₃)₄]SO₄·H₂O, by adding excess concentrated ammonia solution to copper(II) sulfate solution and then adding ethanol.
   Describe what happens when concentrated hydrochloric acid is added to aqueous copper(II) sulfate. Include an equation and the change in shape of the complex ion.3 marks