posted by Val on .
For the following electrochemical cell, what is the correct, balanced reaction?
Cu(s) | Cu2+(aq) || Ag+(aq) | Ag(s)
A. Cu(s) + Cu2+(aq) → Ag+(aq) + Ag(s)
B. Cu(s) + Ag+(aq) → Cu2+(aq) + Ag(s)
C. Cu(s) + 2 Ag+(aq) → Cu2+(aq) + 2 Ag(s)
D. Cu2+(aq) + Ag(s) → Cu(s) + Ag+(aq)
My guess is Answer D
For the following electrochemical cell, what is ΔEº?
Zn(s) | Zn2+(aq) || Cr3+(aq), Cr2+(aq) |Pt(s)
Zn2+(aq) + 2 e- → Zn(s) Eº = -0.8 V
Cr3+ (aq) + e- → Cr2+(aq) Eº = -0.4 V
A. 0.4 V
B. 0.0 V
C. -0.4 V
D. -1.2 V
I am guess it is C..but I am pretty confused about how to solve this--if someone could explain this that'd be great. I changed the sign of the 2nd half reaction so it would be an oxidation (i think..) then added...but I could really use clarification.
Which of the following reagents is most likely to function as a reducing agent?
A. F2(g) F2(g) + 2 e- → 2 F-(aq) Eº = 2.9 V
B. H2(g) 2 H+(aq) + 2 e- → H2(g) Eº = 0 V
C. Al(s) Al3+ (aq) + 3 e- → Al(s) Eº = -1.7 V
D. They are all equally likely
I am guessing it would be C because it has more negative standard reduction potential, so there will be oxidation and it will be a redcing agent? I keep getting mixed up...Thanks for any help
Your "guess" on 1 is correct, but why guess? I suppose you were just kidding and that you worked it out.
On #2, no. You wrote the correct equation for the first one, now do that for the second one.
Zn + 2Cr^+3 ==> Zn^+2 + 2Cr^+2
Zn ==> Zn^+2e Eo as an oxidation is +0.8
Cr^+3 + e ==> Cr^+2 Eo as a redn is -0.4
Add them together.
Ecell = Eo(oxdn) + Eo(redn) = +0.4
A + Eo means the reaction takes place spontaneously. Eo is - means the cell will not go spontaneously but will if the reactions are reversed.
On the third one you are correct. It IS easy to get confused and I do, too, because I learned all of this with all of my tables written as oxidations and not reductions. So I cheat a little. Since my tables run from a high + voltage to a more negative - voltage, the ones at the top Zn, Al, etc, are reducing agents. So I turn the three reactions around in my mind and look for the one with the largest + sign. That is Al. You look for the one with the most negative sign. But you're doing it right.
Which of the following are correct symbols and charges? Could be as many as 5.