Ligand exchange and the chelate effectEdexcel International A Level Chemistry: Flashcards
What these 14 flashcards ask
- What is a ligand exchange reaction?
- What is observed when a few drops of ammonia are added to aqueous copper(II) ions?
- What is observed when excess ammonia is added to the precipitate?
- Why does ammonia form the precipitate with [Cu(H₂O)₆]²⁺?
- What happens to [Cu(H₂O)₆]²⁺ with concentrated HCl?
- What happens to [Co(H₂O)₆]²⁺ with concentrated HCl?
- Why does the coordination number fall from 6 to 4 with chloride?
- How can the colour changes with chloride be reversed?
- Name examples of monodentate, bidentate and hexadentate ligands.
- What is the chelate effect?
- Why is ΔSsystem positive when 3en replace 6NH₃ in [Ni(NH₃)₆]²⁺?
- Why is ΔH about zero in chelate substitutions?
- How do you calculate ΔStotal?
- Why is ethanol added when preparing [Cu(NH₃)₄]SO₄·H₂O?
Exam questions on Ligand exchange and the chelate effect
- 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
- 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
- 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
Written by the Exaim team, led by Shaun Daswani (Head of Upper Secondary, Improve ME Institute; MSc Financial Mathematics, Imperial College London; BSc, UCL) and Jason Daswani (operational lead, Improve ME Institute; LSE).