Why Do Electrons Matter in Electrochemistry?
In any redox reaction, oxidation and reduction happen simultaneously:
- Oxidation is the loss of electrons.
- Reduction is the gain of electrons.
To remember this, use the mnemonic OIL RIG:
- Oxidation Is Loss (of electrons).
- Reduction Is Gain (of electrons).
In electrochemical cells, these processes are separated into two locations: the anode and the cathode. Let’s explore how this works.
Oxidation at the Anode
The anode is where oxidation occurs. At this electrode:
- A species loses electrons, which are then transferred through an external circuit.
- The electrons flow away from the anode toward the cathode.
In a zinc–copper voltaic cell:
- At the zinc anode: $$Zn(s) \rightarrow Zn^{2+}(aq) + 2e^-$$
- Zinc is oxidized, releasing electrons.
- Students often confuse the anode as always being "negative."
- This is true for voltaic cells but not for electrolytic cells.
- Always consider the type of cell before assigning polarity.
Reduction at the Cathode
- The cathode is where reduction occurs.
- At this electrode a species gains electrons from the external circuit.
