Cu2+(aq) + Fe2+(aq)Practice Problem 11
Which of the following pairs of ions cannot exist simultaneously in aqueous solutions?
(a) Cu+ and Fe3+ (b) Fe3+ and I- (c) Al3+ and Co2+
Answer
(a) The Cu+ ion is a significantly better reducing agent than the Fe2+ ion and the Fe3+ ion is a better oxidizing agent than Cu2+. Solutions that contain both Cu+ and Fe3+ ions therefore should undergo a spontaneous oxidation-reduction reaction. As a result, these ions can't exist simultaneously in the same solution:
Cu+(aq) + Fe3+(aq) Cu2+(aq) + Fe2+(aq)
(b) The Fe3+ ion is strong enough to oxidize I- ions to I2. These ions therefore cannot exist in the same solution:
2 Fe3+(aq) + 2 I-(aq) 2 Fe2+(aq) + I2(aq)
(c) The Al3+ ion is one of the weakest oxidizing agents and the Co2+ ion is one of the weakest reducing agents. These ions can't undergo an oxidation-reduction reaction and can therefore coexist in aqueous solution:
Al3+(aq) + Co2+(aq) NR
