Understanding Oxidation
* Oxidation is the loss of electrons. This means an atom or ion is becoming more positive in charge.
* Think of OIL RIG: Oxidation Is Loss (of electrons), Reduction Is Gain (of electrons).
Identifying Oxidation in a Redox Reaction
1. Assign Oxidation Numbers: The first step is to determine the oxidation numbers of all the atoms in the reactants and products. You can use the following rules:
* The oxidation number of an element in its elemental state is always 0.
* The oxidation number of a monatomic ion is equal to its charge.
* The sum of oxidation numbers in a neutral compound must equal zero.
* The sum of oxidation numbers in a polyatomic ion must equal the charge of the ion.
2. Look for Changes in Oxidation Numbers:
* Identify the atoms whose oxidation numbers have increased. These are the atoms that have been oxidized.
Example:
Let's take the reaction of zinc with hydrochloric acid:
Zn(s) + 2HCl(aq) → ZnCl₂(aq) + H₂(g)
* Reactants:
* Zn (elemental): Oxidation number = 0
* H in HCl: Oxidation number = +1
* Cl in HCl: Oxidation number = -1
* Products:
* Zn in ZnCl₂: Oxidation number = +2
* H in H₂: Oxidation number = 0
* Cl in ZnCl₂: Oxidation number = -1
* Observation: The oxidation number of zinc increased from 0 to +2. This means zinc was oxidized.
Important Note:
* Redox reactions always involve both oxidation and reduction. While you're focusing on the oxidation part, remember that there's also an atom or ion that's being reduced (gaining electrons) in the same reaction.
