the extraction of aluminum Flashcards
How reactive is aluminum?
It is less reactive than magnesium but more reactive than zinc or iron
Why can carbon not be used in the extraction of aluminum?
Because it is not reactive enough
What process is used to extract aluminum?
Electrolysis
What is the compound electrolysed when extracting aluminum?
Aluminum oxide (Al2O3)
What ore is aluminum extracted from?
Bauxite
How is the ore for aluminum extraction mined?
By open cast mining
What is the first step in the extraction of aluminum?
To separate the aluminum oxide from the ore, which contains a lot of rocky impurities such as iron(III) oxide
What happens to the rusty brown waste solution?
It has to be stored in large lagoons
Why is the aluminum oxide melted before it is electrolysed?
This enables the ions to move to the electrodes
What is the disadvantage of having to melt the aluminum oxide?
It has a very high melting point of 2050ºC, which uses a lot of energy
How can some of the energy by saved when melting this aluminum oxide?
By mixing it with molten cryolite
What is cryolite?
Another ionic compound
At what temperature can the new molten mixture be melted?
At about 850ºC
What keeps the mixture molten?
The electrical energy transferred to the electrolysis cells
What is the overall reaction in the electrolysis cell when extracting aluminum?
aluminum oxide, 2Al2O3 (l) –> aluminum, 4Al (l) + oxygen, 3O2(g)
What are some uses of aluminium or its alloys?
- overhead power cables
- airplanes
- drink cans
- bicycle frames
- car bodies
What happens at the cathodes in the electrolysis of aluminium oxide?
Each aluminium ion (Al^3+) gains 3 electrons, which turns the ions into aluminium atoms. Therefore the Al^3+ ions are said to have been reduced (as they gain electrons) or form Al atoms
What is the half equation at the cathodes for the electrolysis of aluminium oxide?
Al^3+ (l) + 3e^- ––> Al (l)
What happens to the aluminium metal formed?
It is molten at the temperature of the cell and collects at the bottom, where it is siphoned or tapped off
What happens at the anodes in the electrolysis of alumium oxide?
Each oxide ion (O^2-) loses 2 electrons, which turns them into oxygen atoms. The O^2- ions are said to have been oxidised to form oxygen atoms, which bond in pairs to form molecules of oxygen gas (O2)
What is the half equation at the anodes for the electrolysis of aluminium oxide?
2O^2- (l) ––> O2 (g) + 4e^-
What happens to the oxygen formed at the anodes?
It reacts with the hot carbon anodes, making carbon dioxide gas
What is the half equation for making carbon dioxide gas from the carbon anodes and oxygen gas formed?
C (s) + O2 (g) ––> CO2 (g)
What happens to the carbon anodes?
They gradually burn away, and so they need to be replaced in the cells regularly
