For the following electrochemical cell, what is the correct, balanced reaction?

Question

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

Answer 1

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.

Answer 2

Which of the following are correct symbols and charges? Could be as many as 5.
1. Na-
2. Ag+
3. O2-
4. Ag-
5. NO3-
6. Cu2+
7. F+
8. Cl2-