Balancing a redox reaction

  • #1
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Please post this type of questions in the HW section using the template.
Hi there:

I'm trying to balance a reaction in which methane is oxidized by citric acid in solution. Both methane and citric acid will be transformed into carbon dioxide. To begin, I checked that the reaction is indeed a redox reaction.

C6H8O7→CO2

So, I calculated the oxidation number for carbon goes from +6 to +4. A reduction.

CH4→CO2

I calculated the oxidation number for carbon goes from -4 to +4. An oxidation. This seems reasonable so far. Then, I balanced my half-reactions.

C6H8O7+5H2O→6CO2+18H++18e-

CH4+2H2O→CO2+8H++8e-

Now comes the part that has me baffled. How do I combine these half-reactions and not end up with loads of electrons since they are on the right hand side of both half-reactions?! Clearly, I've done something very wrong. Any help would be appreciated.
 

Answers and Replies

  • #2
Borek
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So, I calculated the oxidation number for carbon goes from +6 to +4
Which carbon?
 
  • #3
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Which carbon?
I meant the citric acid carbon, but clearly I've miscalculated. Consequently, both half reactions are actually oxidation reactions and the overall reaction is nonsensical.
 
  • #4
Borek
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I meant the citric acid carbon
Oxidation number is a property of a single atom, it is quite possible for different atoms of an element to have different oxidation numbers in the molecule, hence your initial statement didn't make much sense

Technically it is not impossible to both oxidize the methane and reduce the citric acid at the same time, producing a "redox reaction". I doubt it would be spontaneous though.
 

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