1. Limited time only! Sign up for a free 30min personal tutor trial with Chegg Tutors
    Dismiss Notice
Dismiss Notice
Join Physics Forums Today!
The friendliest, high quality science and math community on the planet! Everyone who loves science is here!

Homework Help: Half Reaction Method

  1. Jun 17, 2009 #1
    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 [Broken]
    Last edited by a moderator: May 4, 2017
  2. jcsd
  3. Jun 17, 2009 #2
    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!
Share this great discussion with others via Reddit, Google+, Twitter, or Facebook