Chemistry A2 · Electrochemistry. The idea in plain words, the rules to remember, the mistake to avoid and a worked example, written and checked by Mega Lecture.
In electrolysis, an electric current breaks down an electrolyte. Positive ions move to the cathode (negative electrode) and gain electrons. Negative ions move to the anode (positive electrode) and lose electrons.
A molten salt contains only its own ions, so the products are easy to predict. An aqueous solution also contains water, which can be reduced to hydrogen or oxidised to oxygen. The product then depends on electrode potentials and on concentration.
The amount of product depends on the charge passed. One mole of electrons carries a charge of one faraday, 96 500 C.
Students use time in minutes or forget the number of electrons in the half-equation. Change time to seconds, and divide the moles of electrons by 2 for Cu or H2, by 3 for Al and by 4 for O2.
Answer: 0.239 dm3 of chlorine
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