Electrolysis notes Flashcards
Define electrolysis.
Using electricity to decompose something.
We can extract aluminium (Al) from ______________________________ (__________) from its ore (__________).
molten aluminium oxide (Al2O3), bauxite
Name a substance that is used to facilitate the electrolysis of molten aluminium oxide. Explain how it helps.
The melting point of Al2O3 is over 2000°C; it would be very expensive to heat it to this temperature. Therefore, Al2O3 is dissolved in molten cryolite to lower the melting point. This allows electrolysis to happen at about 950°C, which reduces the energy required and the energy cost.
Name the word and chemical half-equation of the reaction that happens at the negative electrode during the electrolysis of aluminium oxide. Describe what happens here.
aluminium ions + electrons —electricity—> aluminium
Al³⁺ + 3e⁻ —electricity—> Al
During electrolysis, Al is produced in molten form at the negative electrode. The molten Al sinks to the bottom of the tank and runs off at intervals.
Name the word and chemical half-equation of the reaction that happens at the positive electrode during the electrolysis of aluminium oxide. Describe what happens here.
Oxygen (O2) is produced at the positive electrode. The O2 reacts with the carbon electrodes to form carbon dioxide (CO2). This reaction wears away the carbon electrodes and they need to be replaced periodically.
oxide ions —electricity—> oxygen + electrons
2O²⁻ —electricity—> O2 + 4e⁻
Name the chemical equation of the overall chemical reaction that happens during the electrolysis of aluminium oxide.
2Al2O3 —electricity—> 4Al + 3O2
Name the general word equation of the overall chemical reaction that happens during electrolysis.
metal compound —electricity—> metal + other element
What is the difference between full and half equations? Name a benefit of half equations.
Full equations involve both elements involved in a process, while half equations only involve one. We can observe the role of electrons in half equations.
Why is aluminium extracted from the electrolysis of its molten ore, but not heating the ore alone?
This is because it is more reactive and cannot be extracted by only heating its ore.
Why must aluminium oxide be melted for electrolysis to occur?
This is because the ions must be free to move for the extraction of aluminium. Since the ore is a solid, the ions in the aluminium oxide cannot move freely, therefore we need to metal the ore into a liquid state for the ions to be able to move for electrolysis to occur.
