Adding H20 and OH-/H+

[Rob Tsai 2F]

I am confused about exactly what methodology to go about adding OH-/H+ and H20 to balance half reactions. Is there a certain procedure for adding H20 to one side and OH-/H+ to the other? The sapling feedback on the homework is giving me contrary statements as to how to go about these problems.

[Yichen Fan 3A]

Based on how I did the sapling questions, you add H+ on either side if you need extra hydrogen atoms and if the solution is acidic, you're done. If the solution is basic, add equal amount of OH- to neutralize that H+ and you will get one side with H2O and the other side with OH-. If you need extra x moles of oxygen atoms, add 2x moles of the OH- to that side and x moles of H2O on the other side in basic solution. If the solution is acidic, add x moles of H2O on the side you need oxygen atoms, and proportional moles of H+ on the other side. No sure if there is a simpler rule, but I got the questions right using this procedure. :)

[alette1a]

Here's the step-by-step I wrote down from Matthew's workshop:
1. identify oxidized/reduced species
2. separate into half-rxns
3. balance half-rxns in acidic or basic conditions...

for acidic:
1. balance O with H2O
2. balance H with H+
3. add e-

for basic:
1. balance O with H2O
2. balance H with H+
3. combine H+ and OH- to form H2O
4. add e-

4. balance the number of e- transferred so they are equal for the half-rxns
5. add the half-rxns together
6. check charges and that the overall rxn is balanced

[Catie Donohue 2K]

Some important things to remember are that you balance non oxygen/hydrogen atoms first. Then, you use H2O to balance oxygen, followed by your ions (either H+ or OH-). If the solution is acidic, use H+. If the solution is basic, use OH-. After adding electrons, the charges and number of each type of atom should be the same on both sides of the reaction.