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Topic: How do I balance a skeleton equation using the half reaction method?  (Read 9679 times)

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Xovan

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Hi I'm having a bit of trouble figureing out a certain problem.  Its in a basic solution.
AsO43-  + NO2- -->  AsO2- + NO3-
The thing is to balance out the equation using the half reaction method.  I know its probably As losing 2e- but what is gaining electrons?  If nothing then why is there 2 spectator ions?

How would adding H2O and H+ change things?
I figure the change in configuration of NO2- and NO3- has something to do with it but I don't see what exactly.

edited for objectional title, and new thoughts
« Last Edit: May 29, 2006, 10:08:54 PM by Xovan »

Offline wereworm73

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Actually, the arsenic atom gained 2 electrons.  Its oxidation state went from 5+ to 3+.  The nitrogen, on the other hand, lost 2 electrons, going from 3+ to 5+.

As for H+ & H2O, look at the number of oxygens & total charge on each side of your equation.  It's not quite balanced, though you can balance this if you include the H+ & H2O.

Xovan

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Thanks for the correction.

Therefor...
AsO4 + 4H+ + 2e- --> AsO2 + 2H2O is reduced and As is the Oxidizing Agent
NO2 + H2O --> NO3 + 2H+ + 2e- is oxidized and N is the Reducing Agent
AsO4+ 4H+ + 2e- + NO2 + H2O --> AsO2 + 2H2O + NO3 + 2H+ + 2e-

right?

Offline wereworm73

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 :)  You got it.

Though you just need to cancel out some things and leave the charges on.  So you can write...

AsO43- + 4H+ + 2e- + NO2- + H2O --> AsO2- + 2H2O + NO3- + 2H+ + 2e-

...as this:

AsO43- + 2H+ +  NO2-  --> AsO2- + H2O + NO3-

Xovan

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Thanks for the help.
Though I didn't write the charges because I was tired of writing sup /sup and sub /sub.
:D

Thanks again for the help.

Offline Borek

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