medium difficulty9 min

Galvanic or Voltaic Cells

A galvanic or voltaic cell is an electrochemical cell in which a spontaneous redox reaction converts chemical energy into electrical energy.

In one line: AnOx and RedCat: oxidation at anode, reduction at cathode.

Practice This Concept

Understand it

In a galvanic cell, oxidation occurs at the anode and reduction occurs at the cathode.
In the Daniell cell, zinc metal loses electrons to form zinc ions, while copper ions gain electrons to form copper metal.
Electrons move through the external circuit from zinc to copper, while ions move through the salt bridge to maintain electrical neutrality in both half-cells.
The salt bridge does not supply electrons; it completes the internal ionic circuit and prevents charge build-up.

Example

Daniell cell notation is Zn(s) | Zn²⁺(aq) || Cu²⁺(aq) | Cu(s). Zinc is the anode, copper is the cathode, and electrons flow from Zn electrode to Cu electrode through the wire.

Rule to remember

Cell notation rule: anode | anode ion || cathode ion | cathode.

Oxidation half-reaction for Daniell cell: Zn(s) → Zn²⁺(aq) + 2e⁻.

Reduction half-reaction: Cu²⁺(aq) + 2e⁻ → Cu(s).

Overall reaction: Zn(s) + Cu²⁺(aq) → Zn²⁺(aq) + Cu(s).

See it worked out

Follow the example line by line, then use the same method on new questions.

Worked example

For the cell Zn | Zn²⁺ || Cu²⁺ | Cu, identify the electrode reactions.

1Since zinc is on the left, it acts as anode: Zn(s) → Zn²⁺ + 2e⁻.
2Copper ion is reduced at the cathode: Cu²⁺ + 2e⁻ → Cu(s).
3Adding gives Zn(s) + Cu²⁺(aq) → Zn²⁺(aq) + Cu(s).

Method you can reuse

1First identify the two redox couples.
2Next decide which species is oxidised and which is reduced using reactivity or electrode potential data.
3Then assign anode to oxidation and cathode to reduction.
4Finally write the cell notation with salt bridge symbol between the two half-cells.

Visual tip

A diagram should show two beakers, Zn electrode in Zn²⁺ solution, Cu electrode in Cu²⁺ solution, salt bridge between solutions, voltmeter in external circuit, electron flow from Zn to Cu, and ion migration through salt bridge.

Check yourself

Answer the question in your head before opening the answer.

Try it yourself

In the Daniell cell Zn | Zn²⁺ || Cu²⁺ | Cu, which electrode is the anode and why?

Think first, then show answer

Zinc is the anode because Zn atoms undergo oxidation: Zn(s) → Zn²⁺(aq) + 2e⁻.

Common wrong answer

A common wrong answer is assigning copper as anode in the Daniell cell because copper appears on the right side of the diagram, or saying salt bridge carries electrons.

Don't mix this up

Students often say that electrons pass through the salt bridge. Electrons move through the external wire; ions from the salt bridge move into the solutions to maintain neutrality.

Exam tip

For any cell notation, read the left half-cell as anode and the right half-cell as cathode unless the question gives a different convention. Link oxidation with anode and reduction with cathode before writing reactions.

Write it in the exam

Each point is worth about one mark. Write point 1 for a 1-mark question and keep adding points as the marks go up.

How CBSE asks it

Questions usually ask students to label anode, cathode, electron flow, salt bridge function, cell reaction, or cell notation for a given redox pair.

1
Enough for 1 mark
A galvanic or voltaic cell is an electrochemical cell in which a spontaneous redox reaction converts chemical energy into electrical energy.
2
Add for 2 marks
Example: Daniell cell notation is Zn(s) | Zn²⁺(aq) || Cu²⁺(aq) | Cu(s). Zinc is the anode, copper is the cathode, and electrons flow from Zn electrode to Cu electrode through the wire.
3
Add for 3 marks
In a galvanic cell, oxidation occurs at the anode and reduction occurs at the cathode.

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