Cambridge O Level Chemistry · Syllabus 5070 · Electrochemistry
Electrolysis
What is Electrolysis?
The decomposition of an ionic compound, either molten or in aqueous solution, brought about by passing an electric current through it. Charge is carried through the external circuit by electrons and through the compound itself by mobile ions, which gain or lose electrons at the electrodes and are released there as new substances.
This definition is part of the Electrochemistry chapter in Cambridge O Level Chemistry.
Electrolysis in context
Electrolysis is the decomposition of an ionic compound, when molten or in aqueous solution, by the passage of an electric current. Everything else in this chapter follows from one question asked in order: where can charge move, which electrode does each ion reach, what happens there, and what would you see? Read this map in seven to ten minutes before the lessons, and again the night before the paper.
Common mistakes with Electrolysis
- 5. "Molten and aqueous electrolysis work the same way." Repair A molten compound supplies only its own two ions, but an aqueous solution has water present as well, so the solution, its concentration and the electrode material can all change the answer. Taught in Lesson D.
Questions students ask about Electrolysis
What is electrolysis?
Electrolysis is the decomposition of an ionic compound, when molten or in aqueous solution, by the passage of an electric current. The electrolyte is the molten or aqueous substance being decomposed; its mobile ions carry charge inside the cell. Cations move to the negative cathode and gain electrons, anions move to the positive anode and lose electrons, and the products are released at the electrode surfaces. At the cathode either a metal or hydrogen is formed; at the anode a non-metal other than hydrogen is formed.
Do electrons flow through the electrolyte during electrolysis?
No. Electrons move only in the external metallic circuit: they leave the negative terminal of the power supply, travel along the wire to the cathode, and electrons released at the anode travel back to the positive terminal. Inside the electrolyte charge is carried by mobile ions and by nothing else: positive cations move to the negative cathode and negative anions move to the positive anode, because opposite charges attract. The two carriers meet only at the electrode surfaces, where an ion gains or loses electrons.