# How to balance equations for reduction/oxidation reaction?

##### 2 Answers

One way is to use the ion-electron method.

#### Explanation:

**EXAMPLE in ACID SOLUTION**

Write the balanced chemical equation for the reaction between potassium permanganate and iodide ion in aqueous sulfuric acid to form potassium iodide and manganese(II) sulfate?

**1. Write the word equation.**

Potassium permanganate + potassium iodide + sulfuric acid → iodine + potassium sulfate

**2. Write the skeleton “molecular” equation.**

**3. Determine the oxidation numbers** of each atom on both sides of the equation.

Left hand side:

Right hand side:

**4. Identify the atoms for which the oxidation number changes.**

**5. Write the “skeleton” ionic equation,** including only those ions for which an atom has changed oxidation number.

**6. Separate the skeleton ionic equation into two half-reactions.**

**7. Balance all atoms other than #"O"# and #"H"#** in each of the half-reactions.

**8. Balance #"O"#** by adding

**9. Balance #"H"#** by adding

**10. Balance charge** by adding electrons to the appropriate side.

The first half-reaction has 7+ on the left and 2+ on the right.

We add

The second half-reaction has 2- on the left and zero on the right.

We add

**11. Multiply the two half-reactions** by a number that gives the lowest common multiple of the electrons transferred in each half-reaction.

In this case, the lowest common multiple of

**12. Add the two half-reactions**, cancelling species that appear on each side of the overall equation.

**13. Check that atoms are balanced.**

Left hand side:

Right hand side:

**14. Check that charges are balanced.**

Left hand side:

Right hand side:

The balanced equation is

**15. Add the spectator ions** to get the "molecular" equation.

Here's how you balance in basic solution.

#### Explanation:

You can first balance the equation **as if** it were in acid and then make a final change to convert it to basic conditions.

Balance the following equation in basic solution:

**1. Determine the oxidation numbers of each atom.**

Left hand side:

Right hand side:

**2.** Identify the atoms for which the **oxidation number changes**.

**3.** Separate the skeleton ionic equation into **two half-reactions**.

**4. Balance all atoms other than**

Done.

**5.** Balance **add #"H"_2"O"# molecules** to the appropriate side.

**9. Balance #"H"#: add #"H"^+# ions** to the appropriate side.

**10. Balance charge: add electrons** to the appropriate side.

**11. Multiply the two half-reactions** by a number that gives the lowest common multiple of the electrons transferred in each half-reaction.

The lowest common multiple of

**12. Add the two half-reactions**, cancelling species that appear on each side of the overall equation.

**13. Convert to base:** add enough multiples of the equation

Our equation has

**14. Check that atoms are balanced.**

Left hand side:

Right hand side:

**15. Check that charges are balanced.**

Left hand side:

Right hand side:

The balanced equation in basic solution is