Part 1: Defining Oxidation and Reduction
The definition of redox has evolved to become more comprehensive. We’ll look at three ways to define it, with the electron transfer definition being the most powerful for electrolysis.
| Definition | Oxidation | Reduction | Mnemonic |
| 1. Oxygen Transfer | Gain of oxygen | Loss of oxygen | Oxidation Is Gain (of oxygen) |
| 2. Hydrogen Transfer | Loss of hydrogen | Gain of hydrogen | Reduction Is Gain (of hydrogen) |
| 3. Electron Transfer | Loss of electrons | Gain of electrons | OIL RIG: Oxidation Is Loss, Reduction Is Gain (of electrons) |
Why the Electron Transfer Definition is Key for Electrolysis:
In electrolysis, an external power source (like a battery) forces electrons to move.
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The positive electrode (anode) is connected to the positive terminal of the power source. It attracts anions (negative ions) and pulls electrons away from them. This is where oxidation (loss of electrons) occurs.
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The negative electrode (cathode) is connected to the negative terminal. It attracts cations (positive ions) and pushes electrons onto them. This is where reduction (gain of electrons) occurs.