Back to 1990: This problem derives from the 22nd IChO that took place in Paris in 1990. It is not a — Physical Chemistry Chemistry Question
Aqueous solutions of copper salts
Back to 1990:
This problem derives from the 22nd IChO that took place in Paris in 1990. It is not a preparatory problem, but it is reported here as a reminiscence of the last IChO organized.
Quote a simple experiment allowing the observation of Cu2O precipitation.
Complex formation involving Cu+ and Cu2+ ions
The dissociation constant of the complex ion [Cu(NH3)2]+ is KD1 = 1×10‒11. Calculate the standard electrode potential E3° of the couple:
[Cu(NH3)2]+(aq) + e− = Cu(s) + 2 NH3(aq)
The standard electrode potential of the couple:
[Cu(NH3)4]2+(aq) + 2 e− = Cu(s) + 4 NH3(aq) is E4° = ‒0.02 V.
Calculate the dissociation constant KD2 of the complex ion [Cu(NH3)4]2+.
Deduce the standard electrode potential E5° of the couple:
[Cu(NH3)4]2+(aq) + e− = [Cu(NH3)2]+(aq) + 2 NH3(aq)
Does the disproportionation of the cation [Cu(NH3)2]+ take place? (Yes/No)
Model Answer
No, since E5° > E4°, the [Cu(NH3)2]+ ion does not disproportionate in standard conditions.