Half-Rxn Method: Answers to My Queries

[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/v...php?tid=12384

 

[vertciel]

Hello there,

Although there are oxygens on both sides of the equation, there are two on the left and three on the right. Therefore, you need to add one water molecule on the left for compensation.

HNO₂ + H₂O -> NO₃^-

Since you have three hydrogen atoms on the reactants' side, add three to the products' side. For balancing half-reactions using this method (Half-Reaction method), it is customary to equilibrate the oxygens first before the hydrogens.

HNO₂ + H₂O -> NO₃^- + 3H⁺

Since there is an excess charge of -2 on the right side, add 2 electrons to ensure that both sides of the equation have the same amount of charge (that is, 0, in this example).

HNO₂ + H₂O -> NO₃^- + 3H⁺ + 2e^-

There you are!

 

[Blueshift5]

Hello there,

I am familiar with the half-rxn method and I am happy to help you with your queries. Let me address your questions one by one.

1) In this particular half-reaction, there are indeed oxygens on both sides. However, the key to balancing a half-reaction is to ensure that the number of atoms of each element is the same on both sides. So, in this case, you would still need to add H2O to compensate for the oxygen atoms. The final balanced half-reaction would be:

HNO2 + H2O --> NO3(-1) + 2H(+)

2) As for the hydrogen on the left, it is important to remember that balancing a half-reaction involves both balancing the atoms and the charges. In this case, the hydrogen atom on the left has a charge of +1, while the hydrogen atom on the right has a charge of 0. To balance the charges, you would need to add 2H(+) on the right side, as shown in the balanced half-reaction above.

I hope this helps clarify your confusion. Balancing half-reactions can be tricky at first, but with practice, it becomes easier. I would also recommend checking out some online tutorials or examples to further solidify your understanding of the half-rxn method.

Best of luck with your studies!