For the following electrochemical cell:
Fe(s) / Fe2+(aq) // MnO4–(aq) Mn2+(aq) / Pt(s)
Which letter corresponds to the correct balanced chemical equation in an acidic solution?
A. 5Fe(s) + 16H+(aq) + 2MnO4–(aq)--> 2Mn2+(aq) + 8H2O(l) + 5Fe2+(aq)
B. Fe(s)+8H+(aq)+MnO4–(aq)+Pt2+(aq)---> Mn2+(aq)+4H2O(l)+Fe2+(aq)+Pt(s)
C. Fe(s) + 8H+(aq) + MnO4–(aq)--->Mn2+(aq) + 4H2O(l) + Fe2+(aq)
D. 2Mn2+(aq) + 8H2O(l) + 5Fe2+(aq)--> 5Fe(s) + 16H+(aq) + 2MnO4–(aq)
E. Mn2+(aq)+4H2O(l)+Fe2+(aq)+Pt(s)----> Fe(s)+8H+(aq)+MnO4–(aq)+Pt2+(aq)
What reaction is occurring at the cathode?
A. 5e– + 8H+(aq)+MnO4–(aq)---> Mn2+(aq) +4H2O(l)
B. Fe(s)---> Fe2+(aq) + 2e–
C. Mn2+(aq) + 4H2O(l)----> 5e– + 8H+(aq) + MnO4–(aq)
D. Fe2+(aq) + 2e– --->Fe(s)
E. Pt(s)---> Pt2+ + 2e
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I read what you said a while ago but i still don't know how to go about the first part. For some reason when i add the reactions I get A
Is the second part B?
6 answers
For part 2, you only need to remember the one definition. Oxidation occurs at the ANODE. So reduction must occur at the cathode (which is what the question asks). Reduction is the gain of electrons, right. Did answer B gain electrons? Nope. Doesn't look like it gained to me. In fact, I see ONLY ONE equation there that gained electrons. So that must the be the right answer. It's past my bed time. I'll stay a minute or two longer to see if this is clear. Please post as soon as you can to let me know
But part 2 is not D. C'mon. I said I saw only one equation that gained electrons. B, your first guess, has electrons on the right hand side which means it is losing electrons which means that is oxidation. Answer D has electrons on the right side which means it is losing electrons and is oxidation. There is only one equation there with electrons on the left side which means that reaction is gaining electrons, that means it is reduction, and that means it is occurring at the cathode.
A. 5e– + 8H+(aq)+MnO4–(aq)---> Mn2+(aq) +4H2O(l)
B. Fe(s)---> Fe2+(aq) + 2e–
C. Mn2+(aq) + 4H2O(l)----> 5e– + 8H+(aq) + MnO4–(aq)
D. Fe2+(aq) + 2e– --->Fe(s)
E. Pt(s)---> Pt2+ + 2e
D doesn't have electrons on the right side and neither does A