Here's an example to illustrate how to determine oxidation states and identify redox reactions:
Example: Consider the reaction between potassium permanganate (KMnO4) and hydrogen peroxide (H2O2) in an acidic solution:
KMnO4 + H2O2 + H+ → K+ + Mn2+ + O2 + H2O
Determine the oxidation states of each element and identify the redox reaction.
Solution:
To determine the oxidation states, we start by assigning an oxidation state to each atom in the reactants and products. We follow the rules below:
- The oxidation state of an element in its free state is zero.
- The sum of oxidation states in a neutral molecule is zero.
- The sum of oxidation states in a polyatomic ion is equal to the charge on the ion.
- The oxidation state of hydrogen is +1, except when it is combined with a metal, in which case it is -1.
- The oxidation state of oxygen is -2, except in peroxides (such as H2O2) where it is -1.
Let's apply these rules to the reactants and products:
- KMnO4: K has an oxidation state of +1, Mn has an oxidation state of +7, and O has an oxidation state of -2.
- H2O2: H has an oxidation state of +1 and O has an oxidation state of -1.
- H+: H has an oxidation state of +1.
- K+: K has an oxidation state of +1.
- Mn2+: Mn has an oxidation state of +2.
- O2: O has an oxidation state of 0.
- H2O: H has an oxidation state of +1 and O has an oxidation state of -2.
Now, let's analyze the changes in oxidation states during the reaction:
- The oxidation state of Mn decreases from +7 in KMnO4 to +2 in Mn2+. This means that Mn is being reduced, and is gaining electrons (i.e., it is the oxidizing agent).
- The oxidation state of O increases from -1 in H2O2 to 0 in O2. This means that O is being oxidized, and is losing electrons (i.e., it is the reducing agent).
- H+ and K+ do not change oxidation states, so they are not involved in the redox reaction.
Therefore, the overall reaction is a redox reaction where hydrogen peroxide acts as the reducing agent and potassium permanganate acts as the oxidizing agent.
I hope this example helps you understand how to determine oxidation states and identify redox reactions!
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