What you'll be able to do: Describe the parts of a galvanic cell, identify the anode and cathode, and read or write standard cell notation.
Best after: Oxidation Numbers and Balancing Redox Reactions
A galvanic cell takes a reaction that would happen in a single beaker and separates it into two halves, forcing the electrons to travel through a wire. That detour is what turns chemistry into usable electricity.
These are recommended, not required. You can start this lesson at any time.
Drop a strip of zinc into copper(II) sulfate and the reaction happens, but the electrons jump directly from zinc atoms to copper ions at the metal surface and all the energy leaves as heat. Put the zinc in one beaker and the copper in another and connect them with a wire, and the same electrons are forced through the external circuit where they can do work.
Oxidation occurs at the anode and reduction at the cathode, in every electrochemical cell without exception. In a galvanic cell the anode is the source of electrons and is therefore labeled negative, while the cathode is positive. The anode metal typically loses mass as it dissolves; the cathode typically gains mass as metal plates onto it.
As oxidation proceeds, positive ions build up in the anode compartment; as reduction proceeds, positive charge is consumed in the cathode compartment. Without relief, the charge imbalance would stop the reaction almost immediately. The salt bridge, usually a gel of an inert electrolyte such as KNO₃, releases anions toward the anode and cations toward the cathode to keep both solutions neutral.
anions → anode, cations → cathode
The convention is anode | anode solution || cathode solution | cathode. A single vertical line marks a phase boundary, a double vertical line marks the salt bridge, and a comma separates two species in the same phase. Concentrations and pressures are written in parentheses when they are not standard.
Zn(s) | Zn²⁺(1 M) || Cu²⁺(1 M) | Cu(s)
Some half-reactions have no solid conductor of their own. The Fe³⁺/Fe²⁺ couple is entirely dissolved, and the hydrogen electrode involves a gas. In those cases a platinum or graphite electrode provides the surface for electron transfer without taking part chemically, and it is written explicitly at the outer edge of the notation.
Pt(s) | Fe²⁺(aq), Fe³⁺(aq) || ...
Given a picture, work outward from the wire. Whichever electrode electrons leave is the anode. Whichever half-cell shows a metal dissolving is oxidation. Once you have the anode, everything else follows: the other electrode is the cathode, the electron flow is anode to cathode externally, and the salt bridge ion flow runs the opposite way inside.
A cell in which a spontaneous redox reaction produces electrical energy.
The site of oxidation; negative terminal in a galvanic cell.
The site of reduction; positive terminal in a galvanic cell.
Maintains neutrality; anions travel to the anode, cations to the cathode.
Anode on the left, cathode on the right, double line for the salt bridge.
anode | anode electrolyte || cathode electrolyte | cathode
A cell is built from a zinc strip in 1 M ZnSO₄ and a copper strip in 1 M CuSO₄, connected by a wire and a KNO₃ salt bridge. Identify the anode, the cathode, and the direction of electron flow.
Try it first: Ask which metal is more easily oxidized.
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Write the cell notation for that same cell under standard conditions.
Try it first: Decide which half-cell belongs on the left.
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Write the cell notation for a cell in which Sn²⁺ is oxidized to Sn⁴⁺ and Ag⁺ is reduced to silver metal.
Try it first: Check whether either half-cell lacks a solid conductor.
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Why it's wrong: In a galvanic cell the anode supplies electrons and is negative; only in an electrolytic cell is it positive.
Check instead: Define the anode by oxidation, then assign the sign from the cell type.
Why it's wrong: The salt bridge carries ions; electrons move only through the external wire.
Check instead: Trace electrons through metal and ions through solution.
Why it's wrong: The anode compartment is accumulating positive charge, so it needs anions.
Check instead: Anions to the anode, cations to the cathode.
Why it's wrong: The convention is fixed: anode left, cathode right.
Check instead: Read the notation as the electron path from left to right.
Why it's wrong: There is nothing to conduct electrons without it, so the notation is incomplete.
Check instead: Add Pt or graphite whenever no solid conductor appears in the half-reaction.
No practice questions are available for this topic yet. You can still practice the whole unit.
A galvanic (voltaic) cell converts the energy of a spontaneous redox reaction into electrical work by physically separating oxidation from reduction. Oxidation always occurs at the anode and reduction always occurs at the cathode. Electrons flow through the external wire from anode to cathode, while the salt bridge carries ions internally to keep both compartments electrically neutral: anions migrate toward the anode and cations toward the cathode. In a galvanic cell the anode is labeled negative and the cathode positive. Cell notation summarizes the whole setup in one line, anode on the left and cathode on the right, with a single vertical line for a phase boundary and a double line for the salt bridge. An inert electrode such as platinum or graphite is written into the notation whenever no solid conductor is otherwise present, for example when both members of a couple are dissolved ions or a gas.
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