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Organizing Reducing/Oxidizing Power

Posted: Tue Mar 12, 2019 11:29 am
by Hai-Lin Yeh 1J
I know the pattern to organize species in reducing/oxidizing power, but when you do, does the wording or specification matter? For example, on test 2, one of the questions was: "rank the following species (Pb, Cd, Mn) in order of increasing reducing power (so more negative, the stronger) going from their neutral to second oxidation state."
Do you have to be concerned with "going from their neutral to second oxidation state" or just ignore it? I flipped the signs of these values because of this statement and got it wrong.

Re: Organizing Reducing/Oxidizing Power

Posted: Tue Mar 12, 2019 2:32 pm
by Manya Bali 4E
I think the wording does matter. For me it was easier to think of it this way. Reducing power means that the substances are being oxidized. Thus increasing reducing power means Eo of oxidation goes from lowest to highest. In this way, the statement "going from their neutral to second oxidation state" makes more sense.

From the Appendix, we get Pt2+ + 2e- -> Pt, Eo = 1.20 V but this is by default the Eo of reduction.
The oxidation reaction would be Pt -> Pt2+ + 2e- and the Eo of oxidation is -1.20 V
Pb2+ + 2e- -> Pb, Eo reduction = -.13 V so the reverse (neutral to 2+) has Eo oxidation of .13 V
Cu2+ + 2e- -> Cu, Eo reduction = .34 V so the reverse (neutral to 2+) has Eo oxidation is -.34 V

Now to place in order from least Eo of oxidation to most: -1.20 V < -.34 V < .13 V or Pt < Cu < Pb

Re: Organizing Reducing/Oxidizing Power

Posted: Wed Mar 13, 2019 2:21 pm
by Hai-Lin Yeh 1J
Does anyone know the specific answer to the question regarding Pb, Cd, Mn? I got Mn < Cd < Pb, but I was marked wrong. Why is that?