Cambridge O Level Chemistry · Syllabus 5070 · Electrochemistry
Electrolyte
What is Electrolyte?
The molten or aqueous substance that is undergoing electrolysis. It contains ions that are free to move, so it conducts electricity, and those moving ions carry charge from one electrode to the other inside the cell.
This definition is part of the Electrochemistry chapter in Cambridge O Level Chemistry.
Common mistakes with Electrolyte
- 1. "Electrons travel through the solution from one electrode to the other." Repair Electrons move only in the external metallic circuit; inside the electrolyte, charge is carried by moving ions and by nothing else. Taught in Lesson A.
Examiner tips on Electrolyte
- Why the lead is written \((l)\). Lead melts at a lower temperature than lead(II) bromide does, so at the temperature needed to keep the electrolyte molten, the lead produced is itself a liquid. That is why the observation is a bead of molten metal rather than a grey solid coating.
Questions students ask about Electrolyte
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.
Which electrode do you connect the object to when electroplating?
The object being plated is made the negative cathode. Metal ions from the electrolyte are reduced onto the object, and reduction happens at the cathode, so connecting the object to the positive terminal would be wrong. The coating metal is made the positive anode, and the electrolyte is a solution containing ions of the coating metal. Electroplating is done for two reasons, and a question asking why wants both: to improve the appearance of a metal object and to improve its resistance to corrosion.