[Part 2]- C6- electrolysis 💧 Flashcards
What can you tell me about the uses and properties of aluminium ? 🛩️
Hint: power lines
- aluminium has a very low density, and is used to make objects from drinks cans to aircraft. [; aircrafts use an alloy of aluminium]
- though aluminium can also be used in power lines as an electrical conductor.
- This is because, it has a delocalised electron, that can carry an electrical charge throughout the whole structure.
What compound is aluminium extracted from ?
- aluminium is extracted from the compound: aluminium oxide [alumina], by electrolysis.
- ; the aluminium oxide is first extracted from an ore called Bauxite.
Describe the electrolysis of aluminium oxide ⚛️
1) aluminium oxide contains the aluminium ion (Al^3+) and the oxide ion (O^2-).
2) ; since it has a very high melting point [of around 2000*c], it’s first mixed with cryolite which lowers the melting point.
3) an electric current is now applied to the molten aluminium oxide and the cathode and anode are both made of graphite [a form of carbon].
4) then the aluminium ions are attracted to the cathode [the negative electrode] and each aluminium ion gains three electrons, forming an aluminium atom.
5) ; the oxide ions, are attracted to the positive terminal [anode] and each oxide ion loses two electrons, forming an oxygen atom.
Why is the first reason why cryolite is used, in the electrolysis of aluminium oxide ?
- cryolite lowers the melting point of aluminium oxide, as it has a low melting point.
- This means, it can be added to the mixture of aluminium oxide, to reduce the overall melting point of the mixture.
- making it easier to melt, and reducing the energy needed for the electrolysis process. [aswell as saving money].
What are the anodes and cathodes made out of, during the electrolysis of aluminium oxide ?
Hint: not carbon
- graphite- this is because, graphite is a good conductor of electricity and has a very high melting point.
- Therefore, it can be used at high temperatures, without melting.
Why must the anode be replaced regularly ?
- the anode needs replaced regularly because, the electrodes are made with carbon [a form of graphite].
- (these electrodes are around 900*c,) and the oxygen molecules produced at the anode, react with the graphite [carbon], forming carbon dioxide gas- gradually oxidising the anodes, as this slowly burns away the anode- therefore adding to the cost of producing aluminium.
Why is producing metals by electrolysis very expensive ?
Hint: melting point, aluminium oxide
- melting the compounds [such as aluminium oxide] requires a great deal of energy because, the melting point of aluminium oxide is high.
- therefore, a lot of energy must be transferred to break its strong ionic bonds- this is expensive.
What is the second reason, why producing metals by electrolysis is expensive ?
Hint: electric current, energy
- the second reason why producing metals by electrolysis is expensive, is because a lot of energy is required to produce the electric current.
What’s another reason why cryolite is used, in the electrolysis of aluminium oxide ?
Hint: conductivity
- the second reason why cryolite is used, in the electrolysis of aluminium oxide, is because:
- it increases the conductivity. Since aluminium oxide is a poor conductor of electricity, it cannot be directly electrolyzed.
- ; Cryolite is a good conductor of electricity, therefore it’s added to the mixture, to increase its conductivity- allowing for the efficient flow of electric current, during the electrolysis process.
What is the half-equation at the cathode [negative electrode], during the electrolysis of aluminium oxide ?
Hint: Al
Al3^+ ➕ 3e^- ——->Al
Why is the half-equation at the cathode, considered a reduction reaction ?
Hint: aluminium oxide, what ion?
- reaction is the loss of oxygen [and gain of electrons]
- at the cathode, the aluminium ion is gaining three electrons, [and forming an aluminium atom]
What is the half-equation at the anode [positive electrode], during the electrolysis of aluminium oxide ?
O^2- ————> O2 + 2e^-
OR
O^2- ➖ 2e^- ———> O
Why is the half-equation at the anode , considered an oxidation reaction ?
Hint: aluminium oxide
- oxidation is the gain of oxygen [and the loss of electrons]
- at the anode, each oxide ions loses two electrons [and forms an oxygen atom]
What other facts can you tell me, about the anode ?
Hint: oxygen
- the oxygen atoms formed at the anode, pair up to form the oxygen molecule O^2. [because oxygen is a diatomic molecule] Therefore, the half-equations at the anode are doubled and are now:
- 2O^2- ————> O2+ 4e^-
OR
2O^2- ➖ 4e^- ———> O2
- Fill in the gaps: during the electrolysis of ______ compounds, positive ions move to the ______ [ ________ electrode] and gain electrons, to form atoms.
- ; negative ____ move to the anode [________ electrode] and ____ electrons, to form atoms.
- This is because opposites attract.
- Fill in the gaps: during the electrolysis of molten compounds, positive ions move to the cathode [**negative ** electrode] and gain electrons, to form atoms.
- ; negative ions move to the anode [positive electrode] and lose electrons, to form atoms.
- This is because opposites attract.
