When electricity is passed through fused ionic compounds or their aqueous solutions, they are decomposed into their constituents. Such compounds are called Electrolytes and the process is called Electrolysis. During electrolysis, a non‑spontaneous chemical reaction takes place with the help of electrical energy.
The process of electrolysis can be carried out in an electrolytic bath called an electrolytic cell with the help of two electrodes through which electric current enters and leaves the cell. These electrodes may be made of graphite or any other metal.
Anode: It is a positive electrode through which electrons enter the external circuit.
Cathode: It is a negative electrode through which electrons leave the external circuit.
Electrolyte present in the cell is in the form of freely moving ions. During electrolysis, the electrolyte is decomposed into its components by applying an external voltage. Thus external voltage source (battery) forces the non‑spontaneous reaction to occur by pumping electrons towards one of the electrodes, thereby, giving it a negative charge. The positive ions of the electrolyte are attracted towards the negative electrode and get reduced by accepting electrons from it, making it the cathode. The battery simultaneously withdraws electrons from the other electrode, giving it a positive charge. The negative ions of the electrolyte are attracted towards this and get oxidized by losing their electrons, making it the anode. Electrons flow in the external circuit while ions move towards their respective electrodes inside the cell. If the oxidation and reduction at the electrodes cease, the flow of electricity in the external circuit also stops.
⚡ Figure 16.2: Electrolysis in an electrolytic cell
(in battery context differs)
(in battery context differs)
Things to know: Battery & electrolytic cell – the terms anode & cathode always refer to oxidation & reduction. However, the charges carried by electrodes in a battery and electrolytic cell are different. (as per attached file)
KEYNOTE: Electrolysis = non‑spontaneous, electrical energy drives reaction.
TRICK: AN OX & RED CAT – Anode = Oxidation, Cathode = Reduction.
MEMORIZE: “Electrons flow from Anode to external circuit” (anode – negative inside cell? but file says: anode positive? Actually in electrolytic cell anode is positive, cathode negative. But electrons leave anode to enter external circuit? file: anode: electrons enter external circuit, so anode is positive. Use mnemonic: PANO – Positive Anode, Oxidation.)