# Balance Half-Cell Equation

1. Jul 5, 2006

### yellowduck

Ok, here is another one I have, this is one of a series of half-cell questions... this one is confusing.

79. Balance the following equations by the half-cell method. Show both half-cell reactions and identify them as oxidation or reduction.
b) Cl2(g) + OH- <=> Cl- + ClO3^- + H2O(l)

Oxidation Reaction:
Cl2 (g) <-> Cl-
2e- + Cl2 <-> 2Cl- --- Balanced Cl molecules and electrons

Reduction Reaction:
Cl2 (g) <-> ClO3-
Cl2 + 6H2O <-> 2ClO3- + 12H+ 10e-

Multiply the oxidation reaction by a factor of 5 to cross out the e-
5Cl2 <-> 10Cl-

6Cl2 + 6H2O <-> 10Cl- + 2ClO3- + 12H+

Since this is a basic solution we must swap out the H+ with OH-... in this case adding 6OH- to each side

6Cl2 + 6H2O + 12OH- <-> 10Cl- + 2ClO3- + 12HOH

This seems kinda insane but it may just be right.
Can anyone give me some input on this?
Thanks.

2. Jul 5, 2006

### Cesium

Ha, I was just reviewing these today.
You can cancel out the H2O since you have it on both sides.

6Cl2 + 12OH- --> 10Cl- + 2ClO3- + 6H2O

You can divide all of the coefficients by 2. It seems that sometimes when you work with diatomic molecules like Cl2 that your final answer will be doubled. I made the same mistake here: https://www.physicsforums.com/showthread.php?t=96870

3Cl2 + 6OH- --> 5Cl- + ClO3- + 3H2O

Copy and paste that line into google and the results show that you're good .

Last edited: Jul 5, 2006
3. Jul 5, 2006

### Gokul43201

Staff Emeritus
This thread is a double-post. The other copy is in Chemistry.

Yellowduck - please do not post multiple copies of the same thing!

4. Jul 6, 2006