Representing Cells
Lajoy Tucker & Dr. Davinder Bhachu
Teachers
Contents
Representing Electrochemical Cells (Cell Notation)
Instead of sketching full laboratory setups for electrochemical cells, chemists often use a concise shorthand to show what is happening. This notation captures the essential information – the substances involved, their states, and the flow of electrons – without the need for complicated diagrams.
Representing Cells Explainer Video
Building from First Principles
1. Start with the half-equations
Each half-cell has a redox equation.
Identify the oxidised species (loses electrons) and the reduced species (gains electrons).
2. Decide which is the anode and cathode
The anode is where oxidation happens (electrons released).
The cathode is where reduction happens (electrons accepted).
Place the anode on the left, cathode on the right.
3. Consider the physical states
Solid metals are written as electrodes.
Aqueous ions are written with (aq).
Gases are written with (g).
If no solid is present in a half-cell, use Pt(s) as an inert conductor.
4. Arrange in notation
On each side, put the reduced form closest to the electrode and the oxidised form nearest the salt bridge.
Separate different phases with |.
Link the two half-cells with || for the salt bridge.
5. Check conventions
Right-hand side should be the reduction half-cell.
Left-hand side should be the oxidation half-cell.
Ensure the species are placed in oxidation state order:
Reduced | Oxidised || Oxidised | Reduced (RO || OR).
Practice Questions
Question 1
Write the conventional cell notation for a cell made from:
A zinc electrode in .
A copper electrode in .
Answer
Zn is oxidised: (anode, left).
Cu²⁺ is reduced: (cathode, right).
Question 2
A hydrogen electrode is connected to a silver electrode in . Write the cell notation.
Answer
half-cell has no solid conductor → Pt.
Silver does the reduction: , so it’s on the right.
Question 3
Construct the cell notation for a magnesium electrode in paired with an iron electrode in .
Answer
Mg has the lower E° and is oxidised: (left).
is reduced to Fe(s) at the cathode (right).
Question 4
Potassium permanganate in acidic solution is coupled with a half-cell. Write the cell notation, remembering to include a platinum electrode where needed.
Answer
Left: (metal electrode present).
Right (acidic permanganate reduction): ; no solid → Pt.
Question 5
Dichromate ions in acidic solution are reduced at the cathode. They are paired with an couple. Write the cell notation.
Answer
Left oxidation: (solution only → Pt).
Right reduction: (solution only → Pt).
Key Rules:
Phase boundaries are written with a single vertical line |.
The salt bridge is shown as a double vertical line ||.
Electrodes appear at the ends of the notation. If there is no solid conducting species in a half-cell, a platinum electrode (Pt) is used.
Species with the highest oxidation state are placed nearest the salt bridge. (Remember: highest oxidation state = most strongly oxidising).
The right-hand side usually represents the half-cell with the higher reduction potential (the cathode).
Commas separate species in the same phase.
No answer provided.
Examples:
1. Zinc–Copper Cell
2. Hydrogen–Copper Cell
3. Bromate–Gold Cell
No answer provided.