Electrolysis Flashcards
What is cryolite
It is added to lower the melting point of the Aluminium oxide and save energy
Which is the positive electrode
Anode
Which is negative electrode
Cathode
What properties of aluminium make it suitable for it to be used as overhead power cables
They are good electrical conductors
Positive ions go to…
- the Cathode which is the negative electrode
- because opposite charges attract
Negative ions go to…
- Anode which is the positive electrode
- because opposite charges attract
Why can’t aluminium be extracted from its ore by reduction with carbon
Aluminium is more reactive than the carbon
How does the use of cryolite during electrolysis help reduce energy costs
Cryolite lowers the melting point of the Aluminium oxide (purified bauxite)
What’s the word equation for the reaction that results in the anode wearing away
Carbon + oxygen —> Carbon Dioxide
What’s the symbol equation for the breakdown of aluminium oxide during electrolysis
Which substance is produced at the anode during the breakdown of aluminium oxide
Oxygen
Which substance is produced at the cathode during the breakdown of aluminium oxide
Aluminium
Why is the extraction of aluminium an expensive process
A lot of heat is required to melt the bauxite and big electrical current
Why do oxide ions collect at the anode
- Oxide ions have a negative charge and attract to the anodes that have a positive charge
- This is because opposite charges attract
Why must the anode be replaced regularly
- oxygen react with carbon anode
- This makes CO2 gas which diffuses away
- the reaction slowly wears away the anode
- so it needs to be replaced
What can be done to conserve natural resources of aluminium
Recycling
Aluminium is used for..
- planes
- car body parts
- bikes
- cans
The main ore of aluminium is ….
Bauxite
Electrolysis is
- Using electrical energy to split up an ionic compound
- (note that ionic compound has to be molten or dissolved in water so ions can move)
What is the electrolite
Anything that’s having electrolysis happening to it
What happens at negative electrode
- it gets electrons pumped out
- these then attract the positive metal ions
- it doesn’t really want it’s electrons back so it takes a lot of energy
What’s happening at the positive electrode
- it is positively charged
- attracts the negatively charged non-metal ions
- electrons return to the battery
- gases are formed (in pairs)
Metals collect at the…
Cathode
Write a half equation for Mg
Mg^2+ + 2e^- —> Mg
Does oxidation or reduction take place at the positive electrode
- oxidation
- because it is losing an electron and oxidation is loss
How do we know what is formed at the negative electrode
- Are they less reactive than hydrogen? (Must say this to get mark)
- They are Au, Ag, Cu, Pt. (Think what can make Jewellery)
How do we know what forms at the positive electrode
1st: halide ions (group 7)
2nd: hydroxide
Never = sulfate, nitrate etc… (they remain in solution) <— remember to say this
What is formed in Copper II chloride solution
Negative electrode: attracts Cu2+, H+
- Cu because it is less reactive than hydrogen
- we can see copper metal and blue colour of solution fade
Positive electrode: attracts Cl-, OH-
- Cl because it is a halide ion
- we can see bubbles and it bleaches damp indicator paper
What is formed in Copper II sulfate solution
the negative electrode: attracts Cu2+, H+
- Cu formed because it is less reactive than hydrogen
- we can see copper metal and blue colour of solution fades
The positive electrode: attracts So4^2-, and OH-
- we get equation4OH^- - 4e^- —> O2 + 2H20
- you see bubbles, you can test for it by relighting a glowing splint
What is formed in sodium chloride solution
Negative electrode: attracts Na+, H+
- H+ is formed because it is less reactive
- you see bubbles and test with squeaky pop
Positive electrode: attracts Cl-, OH-
- forms Cl2
- you can see bubbles and it bleaches damp indicator paper
What is formed in sodium sulfate solution
At negative electrode: attracts Na+, H+
- H is formed because it is less reactive
- you see bubbles and can test with squeaky pop
At positive electrode: attracts So4^2-, OH-
- we get equation4OH^- - 4e^- —> O2 + 2H20
- you see bubbles, you can test for it by relighting a glowing splint
