5.2 Describe and explain the extraction of aluminium from PURIFIED aluminium oxide by electrolysis..

..including:
i. the use of molten cryolite as a solvent and to decrease the required operating temperature
ii. the need to replace positive electrodes
iii. the cost of electricity as a major factor

The extraction
1. Bauxite purified into aluminium oxide
2. Dissolved in molten cryolite - this is an aluminium compound and brings down the boiling point (less electricity needed = less energy needed = less cost). Also a solvent for Al2O3
3. At the negative electrode, aluminium is formed.
4. Oxygen forms at the positive electrode
5. Oxygen reacts with the positive graphite anode and it becomes corroded so it needs to be replaced frequently.

The electricity needed in this process costs a lot of money, so the process tries to use as little electricity as possible (which is a lot, to be honest)

Little key notes

• Formula for aluminium oxide: Al2 O3 (numbers in subscript)
• Equation for this is 2Al2 O3 (l) ---> 4Al (l) + 3O2 (g) (numbers in red are used to balance the equation)
• It forms the ions Al 3+ (which is the cathode [-]  ) and O 2- (which is the anode [+])
• Aluminium normally melts at about 2000 degrees C but in cryolite, it melts at about 900 degrees C
• Uses include aircraft construction (it's low density + strong), cans for drinks (easy to shape + corrosion resistant) and boilers and cookers (good heat conductor)
• An ionic compound will only be able to conduct electricity if it is molten or in an aqueous solution.
• Walls of the thingie (see below) are the negative anodes.
• For electricity to flow, there must be either delocalized electrons or ions that are able to move.

Here's a little diagram I drew that looks kind of depressing but hey, I tried.

Figure 1

See key word quizlet - link on the right hand side menu.