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Assistance needed for teaching redox problems

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Rayen:
Hello, I am a "peer leader" for a General Chemistry help course and this week the students are working on redox... well I do not know a good way in either the half reaction method or the oxidation number method (I am thinking most of my students will be using the half rx method as that is the one that is genearly seen as easier) to work on problems where one of the oxidized or reduced parts end up in, or start out in, two different compounts.    So... here is the equation I need a good clear way of working.  Any suggestions?
in acid:

Cu2Cl2 + HClO --> Cl- + Cu2+

thank-you very much!

Donaldson Tan:
a redox reaction is in fact an exchange of electrons between the oxidation and reduction processes.

In using that reaction as an example, you should teach them how to identy which species have been oxidised and which species have been reduced.

Next, show them you have to balance the half reactions in terms of charge and moles. Explain to them where electrons appear from and where they go.

Then, highlight to them that redox is an exchange process, therefore the number of electrons released by the oxidation process is the number of electrons absorbed by the reduction process.

This is my 2cents worth.

Rayen:
I understand that all right... I guess the more specific question is, when spliting the reaction into the half reactions,

Cu2Cl2 --> Cl- + Cu2+

and (I assume)

HClO --> Cl-

How between the two equations will you be assured that the balancing of the Cl (charge or atom) will not be messed up by it being balanced in two half reactions?  could you split the Cu2Cl2 into ions for the half reactions? and then have the Cl - be with the reduction eq?

xiankai:
yes u could, provided the substances are ionic, of course.

Donaldson Tan:

--- Quote from: Rayen on September 19, 2005, 07:29:51 PM ---Cu2Cl2 --> Cl- + Cu2+

--- End quote ---

I would write Cu2Cl2 --> Cu2+ to highlight copper has been oxidised. the oxidation number of chlorine never changes throughout the reaction.

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