Electrolysis Flashcards
4.4.3.1
Why does a substance need to be molten or aq to undergo electrolysis?
Because then the ions are free to move around within the solution. These liquids / solutions can conduct electricity and are called electrolytes
4.4.3.1
What’s an electrolyte?
The solution / molten substance that undergoes electrolysis
4.4.3.1
What does passing an electric current through the electrolyte do?
Causes the ions to move yo the electrodes
4.4.3.1
What’s the negative electrode called?
Cathode
4.4.3.1
What’s the positive electrode called?
Anode
4.4.3.1
Where do negative ions move to?
Positive electrode
Anode
4.4.3.1
Where do the positive ions move to?
Negative electrode
Cathode
4.4.3.1
What’s electrolysis?
The splitting of a compound (ionic) using electricity.
4.4.3.2
What type of substance is formed at the Cathode
The cathode is negative so it attracts positively charged ions
Metals
4.4.3.2
What type of substance is formed at the Anode
The anode is positive so it attracts negatively charged ions
Non-metals
4.4.3.3
When is electrolysis used?
When the metal is too reactive to be extracted by reduction with carbon
OR
when the metal reacts with carbon (rare that metals react with carbon)
4.4.3.3
How can metals be extracted?
From a molten compound by electrolysis
4.4.3.3
Why is electrolysis expensive?
Because large amounts of energy are used to melt the compound
AND
Because large amounts of energy are used to produce electrical current
4.4.3.3
What substance is added to Al2O3 to lower the melting point?
Cryolite
4.4.3.3
What forms at the anode / cathode from aluminium oxide?
Cathode : aluminium
Anode : oxygen
4.4.3.3
Why do the electrodes need to be replaced during electrolysis of aluminium oxide (Al2O3)?
Because the oxygen formed at the anode (positive electrode) reacts with the carbon so it must be continually replaced.
4.4.3.4
What happens to the ions at the electrodes
They get discharged
4.4.3.4
When is hydrogen produces at the cathode?
In an AQ solution when the metal is MORE reactive than hydrogen
This is because in the AQ solution water molecules break down produces H+ ions
4.4.3.4
When is oxygen produced at the anode?
In an AQ solution When halide ions / halogens are not present
This is because in the AQ solution water molecules break down produces OH-ions
4.4.3.5
What type of reaction occurs at the anode?
The negative ions lose electrons
OXIDATION
4.4.3.5
What type of reaction occurs at the cathode?
The positive ions gain electrons
REDUCTION
4.4.3.5
Half equation for hydrogen
2H+ + 2e- —> H2
4.4.3.5
Half equation for Hydroxide
4OH- - 4e- —> O2 + 2H2O
