Half-Reaction Method: Answers to Questions

[Jules18]

I'm just learning the half-rxn method, so I really hope there's somebody else on this forum who's familiar with it. If anyone needs a refresher, go to the link at the bottom of the post.

One of the "half-rxns" I'm doing is this:

HNO2 --> NO3(-1)

So, I'm confused because
1) There's oxygens on both sides, so I'm not sure if I should still add H2O to compensate for them.
2) What do I do about the hydrogen on the left?

http://www.sciencemadness.org/talk/viewthread.php?tid=12384

 

[Borek]

1) There's oxygens on both sides, so I'm not sure if I should still add H2O to compensate for them.

Yes - you will be not able to balance nitrogen and oxygen at the same time without adding water.

2) What do I do about the hydrogen on the left?

It ends in the water (or OH^-) on the right.

Note: if it happens in water you can always use H⁺, OH^- and H₂O on both sides of the reaction. In the end they will either cancel out, or you can add something to both sides of the reaction to get the same result and be consistent with the pH of teh solution.

For example, if you hane an excess hydrogen on the left, you can assume it end as H⁺ in the products. Later, if you don't want H⁺ in the products, you can add OH^- to both sides - that will mean H⁺+OH^- on the right. That's obviously just water molecule.

balancing using half reaction method