C6 Electrolysis Flashcards
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Oxidation Is Loss Reduction Is Gain
(In terms of electrons)
How do yo extract a metal with carbon?
Using carbon reduction
1) You can only do this with metals that are below carbon in the reactivity series
2) The ore is reduced using carbon
3) The carbon gains the oxygen atom so it has been oxidised
What is a redox reaction?
A reaction which contains an atom loosing and a different atom gaining a electron/s at the same time
Reduction and Oxidation must happen at the same time.
Give an example of a redox reaction
Displacement reactions (when a more reactive atom kicks out a less reactive one in a compound)
What is going through reduction and oxidation in a displacement reaction?
The metal ion is being reduced (the metal in the coupound)
The metal ATOM is oxidising (the metal that is not in the compound)
What is an ionic equasion?
An equasion that only shows the particals that react
What is a spectator in an equasion?
Something that doesn’t change
Ionic equasions take out the spectators
What is electrolysis?
When you seperate 2 solutiions in a electrolyte (an aq solution or a disolved ionic compound)
How does electrolysis work?
The positive ions move towards the cathods (they are reduced) by the negative electric electrons moving through it
The negative ions move towards the anode (they are oxidised) …
The elements become uncharged and are discharged from the electrolyte (solition)
Why can’t a ionic solid be electrolised?
How can youfix this?
Because the atoms are in a fixed place and arn’t able to move around to the cathode/anode
By melting the slid (molten)
What is a way to extract metals from there ores?
Electrolysis
Why is using electrolysis to extract metals from ores bad?
Why might you need to do it?
It is expensive to get the energy to melt the ores and to run energy through them.
The metal is more reactive to be reduced by carbon therefore
Why does the molton solution conduct electiclrity?
It contains free electeons
When electolysis is done on alumninion what is done it it? Why?
It is mixed in cryolite solution to lower it’s melting point so that it is cheeper and easier to melt into a molten solution
What happens at each electrode when electrolysis with aluminion happens?
Cathode (negative electode) Al3 + 3e- = Al
(Reduction)(the metal)
Anode 2O*2- =O+4e-
(Oxidisation)(non metal)
Why do the electrodes in the electolysos of alimunin need to be swapped out regualy?
Because the oxygen being produced reacts with the andoe made out of carbon. This degrades the carbon so it need to be replaced regauly
In the electolysis of aluminion what are the electrodes made out of?
Graphite (carbon)
In the electrolysos of an aq solution when is H+ions produced?
Hydrogen is produced at the cathode if the metal is more reactive than hydrogen
In the electrolysos of an aq solution what is usually prodiced at the anode?
What is the exception?
O2
If the aq solution contains halide ions(halogen), then the halogen will be produced at the anodes eg F*-
What does H^2Osplit into?
H+ and OH-
In the electrolysos of an aq solution Why are there 2 different ions competing at each electrode?
You have the ions of the water and the ions of the ionic compound
What are the half equasions for the electrolysis of Copper III Sulfate?
Copper is less reactive than hydrogen so copper is produced
Cathode - Cu2+ + 2e- = Cu
There are no halide ions so oxygen and water are produced
Anode - 4OH- = O2 +2H2O (water) + 4e-
What are the half equasions of Sodium Chloride?
Sodium is more reactive than hydrogen so hydrogen is produced
Cathode 2H+ + 2e- = H*2
Chloride ions (halide ions) are present so the halogen is produced
Anode 2Cl- = Cl*2 + 2e-
Why does the reaction of H^2O have a special arrow symbol?
Because it is reversable
What happens at the Cathode is H+ ions and metal ions are present?
Hydrogen gass will be produced if the metal ions form an element that is more reactive than hydrogen
A layer of pure metal will be produced if not (if the metal ions form an element that is less reactive than hydrogen
What happens at the anode if OH- ions are present?
Oxygen will produced
However if there is a halide present then the halide will be produced not oxygen
How can you lest for hydrogen?
The squeeky pop test with a lighted splint
How can you test for oxygen?
A substance that contains oxygen will relight a glowing splint
How can you test for chlorine?
It will bleach litmus paper white
What need to be the same woth each half equacion?
The amount of electrons
Give an example of a displacemnt reaction?
Fe(s) + CuSO^4(aq) = FeSO^4(aq) + Cu(s)
Iron + Copper Sulfate = Iron Sulfate + Copper
What are the ionic equasions of the displacement reaction?
Fe = Fe2+ +2e-
Cu2+ + 2e- = Cu
In a displacement reaction what is oxidised?
The metal ion
What is an ionic equasion?
An equasion that just shows the bits that change
What does electrolysis mean? (Litteraly)
“Splitting up with electricity
What happens during electrolysis?
Electricity is passed through a molten or disolved ionic compound
The ions then move towards the electrodes where they react and the coupound decomposes
The positive ions move towards the cathode and gain electrons (reduction)
The negative ions move towards the anode wherw they loose electrons (oxidised)
This creates a flow of charge throught he electrolyte
At the anode and cathode ions gain/loose electrons and form un charged elements and are discharged.
What is the electrolyte?
The solution which electolysis is happening in
Where do positive metal ions go?
The cathode
Where do negative non metal ions go
The anode
Where does the non metal go?
The anode
Where does the metal go?
The cathode
Why might you use electrolysis to extract an ore?
If the metal is too reactive to be reduced with carbon
What are the disadvantages of using elctrolysis?
It is expensive as it requires a lot of energy
What is aluminium extracted from?
How?
From the ore bauxite using electrolysis
What is aluminium mixed with?
Why?
Cryolite
To lower the melting point
Why does the melting point of aluminium need to be lowered?
To make it cheaper to melt (less energy required). It needs to be melted so that the molten form will contain free ions and therefore will conduct electricity
What happens at the negative electrode (the anode)?
In the electorysis of aluminium
Al3+ ions go there where they pick up 3 electrons and turn back into neutral Al atoms.
They then sink to the bottom of the tank
What hapens at the positive electrode (the cathode)?
In the electorysis of aluminium
The O2- ions go to the positive electron where they loose two electrons. The neitral oxygen atoms combine to form O^2 molecules
Why do the anode? need to be replaced often?
It is made of Carbon and therefore it reacts with the oxygen. This degrades it
What is the half equasion at the negative electrode?
In the electorysis of aluminium
Al3+ + 3e- = Al
What is the half equasion at the positive electode?
In the electorysis of aluminium
2O2- = O^2 + 4e-
What is the overall word equasion?
In the electorysis of aluminium
Aluminium oxide = aluminium + oxygen
What is the overall symbol equasion?
In the electorysis of aluminium
2Al^2O^3(l) = 4Al(l) + 3O^2(g)
