1. How to solve, balance, and identify your oxidizing and reducing agents
Redox Reactions
How to solve, balance, and identify your oxidizing and reducing agents

2. What is a redox reaction?
A redox reaction is where ion charge changes from one side of the reaction to the other.
Very often they are reversible reactions.
In a redox reaction there is always an oxidizing agent and a reducing agent.

3. How to Balance a Redox reaction
To balance a redox reaction the first thing to be done is to find all of the charges for every element in the reaction. This will tell us which ion’s charge changes.
KMnO4 + H2S + HCl = KCl + MnCl2 + H2O + S
Once you have the charges you must decide which ion had a charge that changed. Here we can see that Mn went from +7 to +2 and S went from -2 to 0.

4. Balancing a Redox Reaction
Once the elements with the changing charges are identified then we can write a simplified ionic reaction for each one.
Mn electrons = Mn+2
S-2 = S0 + 2 electrons
We can now balance the charges between these two reactions. We must have equal numbers of free electrons. Since we cannot multiply 2 by anything to get 5 we must use the least common multiple, which is 10.

5. Balancing a Redox Reaction
2 ( Mn electrons = Mn+2)
5 (S-2 = S0 + 2 electrons)
This produces: 2 Mn+7, 10 electrons, and 2 Mn+2
Also: 5 S-2, 5 S0, and 10 electrons
We can now take those coefficients and put them into our full equation with the compounds that contained the above ions.
2KMnO4 + 5H2S + HCl = KCl + 2MnCl2 + H2O + 5S
This leaves us with an unbalanced equation so we must balance the rest of the equation with coefficients.
2KMnO4 + 5H2S + 6HCl = 2KCl + 2MnCl2 + 8H2O + 5S

6. How do I Identify the Oxidizing and Reducing Agents?
Oxidizing involves losing electrons so the element that lost electrons is the oxidized element.
Reducing involves gaining electrons so the element that gained electrons is the reduced element.
There is an easy mnemonic device to help you remember: LEO the lion goes GER
LEO: Losing electrons oxidizing
GER: Gain electrons Reducing

7. Oxidized and Reduced Elements
So in our example: Mn was a +7 and became a +2. To write it another way:
Mn electrons = Mn+2
Since Mn gained electrons this makes it our reduced element.
S was a -2 and became a 0, to write it out:
S-2 = S electrons
Since S lost electrons this makes it our oxidized element.

8. So what is the difference between a oxidized element and an oxidizing agent?
The element that loses the electrons is the oxidized element but the element that gained those electrons is the oxidizing agent and vice versa.
So in our example the S was the oxidized element which means that the Mn was the oxidizing agent, it caused S to lose it’s electrons.
To summarize:
S: oxidized element, reducing agent
Mn: reduced element, oxidizing agent