Homework Help: Chemistry, electrochem

Posted by Terry on Sunday, May 11, 2008 at 6:08pm.

(1) Half-reactions are written as ______ reactions with charge and mass balanced.

(2) Among the ions, Cd^2+, Pb^2+ & Ca^2+, ________ has the greatest ability to reduce to its neutral metal.

(3) Among the neutral metals; Pb, Ca & Cd, ________ has the least ability to oxidize to the +2 ion.

I really need help for 2 & 3, but for the first one, half-reactions are written as oxidation reactions, right?

Chemistry, electrochem - DrBob222, Sunday, May 11, 2008 at 7:15pm
I write half reactions as oxidation reactions if that is the way they go in the system or as reduction reactions if that is the way they go. But if the problem is not addressing a specific reaction but the table of potentials, those are written as reduction reactions.[This has been a heated discussion years among chemists with some preferring to write the tables as oxidation and others preferring reduction. As it now stands, the IUPAC has agreed that writing all tables in recution form is will be the standard.
For 2 and 3, look up the activity series in your text or notes. The activity series is a list of metals, not ions, being oxidized with the most reactive on top and the least reactive on bottom.
My text lists the metals in this order:
Ca
Cd
Pb.
That means that Ca is the strongest reducing agent (going to Ca ==> Ca^+2 + 2e). Of course, that means Ca is the easiest to oxidize. That answers #3, but of course you want the one at the bottom of the list if you want the least ability to oxidize. For #2, just reverse the reasoning. If Pb has the least ability to oxidize to the +2 ion, then ____ has the greatest ability for the +2 ion to be reduced.

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