Electrolysis Flashcards
What is electrolysis?
Electrolysis means ‘splitting up with electricity’, this uses an electric current to break down ionic compounds.
What is the compound broken down by electrolysis called?
The compound broken down by electrolysis is called the electrolyte.
In electrolysis, where will the positive ions in the electrolyte move?
The positive ions in the electrolyte will move towards the cathode (the negative electrode) and gain electrons (where they are reduced).
In electrolysis, where will the negative ions in the electrolyte move?
The negative ions in the electrolyte will move towards the anode (the positive electrode) and lose electrons (they are oxidised).
What does OILRIG stand for?
Oxidation
Is
Loss
Reduction
Is
Gain
What does PANiC stand for?
Positive
Anode
Negative
(is)
Cathode
When ions move to the oppositely charged electrode what does this create?
When ions move to the oppositely charged electrode this creates a flow of charge through the electrolyte.
What happens when ions gain or lose electrons?
When ions gain or lose electrons, they form the uncharged element and are discharged from the electrolyte.
Why can’t an ionic solid be electrolysed?
An ionic solid can’t be electrolysed because the ions are in fixed positions and can’t move.
What type of ionic compound can be electrolysed and why?
Molten ionic compounds can be electrolysed because the ions can move freely and conduct electricity.
How do you show how lead bromide is broken up into their elements using half equations?
Example of lead bromide being broke into their elements:
Lead being reduced:
Pb^(2+) + 2e^(-) —> Pb
Bromine being oxidised
2Br^(-) —> Br2 + 2e^(-)
- Look at CGP book to understand how they properly look on pg. 58
What the difference in ions moving to the cathode and anode other than their charges?
- Metal (positive) ions are reduced to the element at cathode
- Non-metal (negative) ions are oxidised to the element at the anode
If a metal is too reactive to be reduced with carbon what happens?
If a metal is too reactive to be reduced with carbon or reacts with carbon then electrolysis can be used to extract it.
What is a disadvantage of electrolysis and why?
Extracting methods via electrolysis is very expensive as lots of energy is required to melt the ore and produce the required current.
What compound does bauxite contain which has aluminium?
Bauxite contains aluminium oxide, Al2O3
How is aluminium extracted from the ore, bauxite, by electrolysis?
- Aluminium is mixed with cryolite
- The molten mixture contains free ions so it’ll conduct electricity
- The positive Al^(3+) ions are attracted to the cathode where they pick up 3 electrons and turn into neutral aluminium atoms
- These atoms then sink to the bottom of electrolysis tank
- The negative o^(2-) ions are attracted to the anode where they lose 2 electrons and the neutral oxygen atoms will combine to form O2 molecules
When extracting aluminium from bauxite by electrolysis, why is cryolite used?
Cryolite is used because aluminium oxide has a very high melting temperature so cryolite is used to lower the melting point.
What is the half equation for aluminium oxide being reduced/oxidised during electrolysis?
Aluminium being reduced:
Al^(3+) + 3e^(-) —> Al
Oxygen being oxidised:
2O^(2-) —> O2 + 4e^(-)
What is the overall equation for aluminium oxide being broken down?
- Aluminium oxide —> aluminium + oxygen
- 2Al2O3(l) —> 4Al(l) + 3O2(g)
What is the anode made of in aluminium oxide electrolysis and what does this mean?
- The anode is made of carbon
- Oxygen reacts with it to produce carbon dioxide
- This means the anode needs to be replaced regularly
When doing electrolysis on aqueous solutions, what else other than the ions will be present?
There will be hydrogen ions and hydroxide ions from the water.
At the cathode, what will happen if the metal ions are more reactive than the hydrogen ions (H^+)?
At the cathode, what will happen if the metal ions are less reactive than the hydrogen ions (H^+)
*At the cathode, if the metal ions are more reactive than the hydrogen ions, hydrogen gas will be produced
* At the cathode, if the metal ions are less reactive than the hydrogen ions, a solid layer of pure metal will be produced
At the anode, what will happen if hydroxide (OH^-) and halide ions are present?
At the anode, what will happen if hydroxide (OH^-) and no halide ions are present?
- At the anode, if hydroxide (OH^-) and halide ions are present, the halogens will be formed
- At the anode, if hydroxide (OH^-) and no halide ions are present, then the hydroxide ions are discharged and oxygen will be formed
When drawing apparatus for an electrolysis experiment, you need to include what power supply?
When drawing apparatus for an electrolysis experiment, you need to include a d.c. (direct current) power supply.
In electrolysis with aqueous solutions, how do you know if oxygen is produced?
At the anode, bubbles will be produced if oxygen is produced.
How test if chlorine was produced at the anode?
Chlorine bleaches damp litmus paper, turning it white.
How test if oxygen was produced at the anode?
Oxygen will relight a glowing splint.
How test if hydrogen was produced at the cathode?
Hydrogen makes a ‘squeaky pop’ with a lighted splint.
What is the half equation if hydrogen is produced at the cathode?
2H^(+) + 2e^(-) —> H2
*Look at pg.59 in CGP book to see it clearer
What is the half equation is chlorine is produced at the anode?
2Cl^(-) —> Cl2 + 2e^(-)
or
2Cl^(-) - 2el^(-) —> Cl2
What is the half equation if hydroxide is produced at the anode?
4OH^(-) —> O2 + 2H2O + 4e^(-)
or
4OH^(-) - 4e^(-) —> O2 + 2H2O
