Cathode

What is Cathode?

The negative electrode of a simple electrolytic cell, joined to the negative terminal of the power supply. The product formed there is always either a metal or hydrogen. For Extended candidates, it is also the electrode at which positive ions arriving from the electrolyte gain electrons, so reduction happens there.

This definition is part of the Electrochemistry chapter in Cambridge IGCSE Chemistry.

Cathode in context

Concepts related to Cathode

• Reduction
• cations
• Anode

Common mistakes with Cathode

• 2. "Positive ions go to the positive anode." Supplement 4.1.8 Repair Opposite charges attract, so positive cations move to the negative cathode and negative anions move to the positive anode. Taught in Lesson A.
• 3. "The anode is positive, in every cell, everywhere." Core 4.1.2 Repair In a simple electrolytic cell the anode is positive and the cathode is negative because an external power supply makes them so; that sign pattern belongs to this context and should not be carried unexamined into other kinds of cell. Taught in Lesson A.
• 4. "Oxidation is gain of electrons." Supplement 4.1.11 Repair Oxidation is loss of electrons and happens at the anode; reduction is gain of electrons and happens at the cathode — write the full words, then check the side your electrons are on. Taught in Lesson F.
• 8. "Connect the spoon you want to plate to the positive terminal." Core 4.1.7 Repair The cathode is the electrode where metal from the solution is deposited, so the object being plated is the negative cathode and the coating metal is the positive anode. Connected the other way round, the object is the electrode that dissolves. Extended candidates can add the electron reason: depositing a metal ion is a reduction, and reduction happens at the cathode Supplement 4.1.11 Taught in Lesson I.

Examiner tips on Cathode

• The arrow that costs marks. A single electron arrow drawn straight from the anode across to the cathode, ignoring the power supply, describes a cell that does not exist. Electrons in an electrolytic cell are pushed by the supply; draw them leaving the negative terminal on one side and arriving at the positive terminal on the other.
• Sodium does not appear. The cathode product here is hydrogen, not sodium, even though sodium ions are the majority cation in the solution. This is the reason the general statement in Lesson C reads "a metal or hydrogen" — in an aqueous cell, hydrogen is a genuine possibility at the cathode.
• A careful way to say it. Write "the anode loses mass and the cathode gains mass" — that is what is observed. Do not claim the two changes are exactly equal unless a question gives you data or a calculation that establishes it.