Comparing reducing agents

Moderators: Chem_Mod, Chem_Admin

Glenda Marshall DIS 3M
Posts: 68
Joined: Sat Sep 27, 2014 3:00 am

Comparing reducing agents

Postby Glenda Marshall DIS 3M » Tue Mar 10, 2015 9:59 pm

In problem 13.25, it asks us to rank the metals given in order of the power of the reducing agent. Part (a) gives us Cu, Zn, Fe, and Cr. I know that the lower the reduction potential the more powerful the reducing agent, but how do we know which reduction potentials to look at to compare their relative strengths. Both have multiple reduction half-reactions listed in the index.
Thanks!

martha-1I
Posts: 76
Joined: Fri Sep 26, 2014 2:02 pm

Re: Comparing reducing agents

Postby martha-1I » Wed Mar 11, 2015 12:34 am

You compare the standard reduction potentials for each one. For example, the reaction to form Cu is Cu+ + e- ----> Cu. According to Appendix 2A in the back of the book, the standard potential for the formation of Cu is EReduction= +0.34V. You follow the same pattern for the rest of the metals and compare their standard potentials. REMINDER: The more negative the standard potential, the stronger the reducing agent.

Chem_Mod
Posts: 18889
Joined: Thu Aug 04, 2011 1:53 pm
Has upvoted: 716 times

Re: Comparing reducing agents

Postby Chem_Mod » Wed Mar 11, 2015 3:06 am

Martha is correct.

The higher the E-red, the more easily the reactant is reduced. The most-easily reduced chemical is equivalent to the best oxidizing agent, or the worst reducing agent. So, turning it around, the best reducing agent corresponds to the lowest E-red.

Glenda Marshall DIS 3M
Posts: 68
Joined: Sat Sep 27, 2014 3:00 am

Re: Comparing reducing agents

Postby Glenda Marshall DIS 3M » Wed Mar 11, 2015 5:06 pm

That makes sense, but I am still confused how you know to use

Cu+ + e- ---> Cu Eo =+0.52

as opposed to

Cu2+ + 2e- ---> Cu Eo = +0.34

Because using the lower one would change the answer. Thanks!

Niharika Reddy 1D
Posts: 127
Joined: Fri Sep 26, 2014 2:02 pm

Re: Comparing reducing agents

Postby Niharika Reddy 1D » Wed Mar 11, 2015 6:12 pm

For this particular question, I don't think the answer is affected by looking at the second Cu half reaction you listed, since both of those reduction potentials are much larger than those of the other metals. When I looked up the half reactions and their standard potentials, I looked at all the half reactions for the M2+ cations, where M is the metal, so I used the second one with a standard reduction potential of .34V

Chem_Mod
Posts: 18889
Joined: Thu Aug 04, 2011 1:53 pm
Has upvoted: 716 times

Re: Comparing reducing agents

Postby Chem_Mod » Wed Mar 11, 2015 6:33 pm

If you have these kind of questions, there must be more information telling you which specific oxidation state you need to compare. Since Cu2+ and Cu+ are different species as reducing agent.


Return to “Galvanic/Voltaic Cells, Calculating Standard Cell Potentials, Cell Diagrams”

Who is online

Users browsing this forum: No registered users and 2 guests