Electrolysis Flashcards
Why can’t solid ionic compounds conduct electricity
Because the ions are locked in place and aren’t free to move, so they can’t carry charge
Why do we melt solid ionic compounds for electrolysis
The forces are broken so the ions are free to move so they can conduct electricity
What is electrolyte
A liquid or solution that can conduct electricity
What does molten mean
Melted
What are electrodes made out of
Usually graphite or a metal
(Needs to conduct electricity)
What is the name of the negative electrode
Cathode
- covered with electrons from energy source
What is the positive electrode called
Anode
- lacks electrons
What is attracted to the cathode
Positive ions
What is attracted to the anode
Negative ions
Which electrode is on the left and which is on the right
Cathode - left
Anode - right
What happens when positive ions are attracted to the cathode
They gain enough electrons to become atoms
- gaining electrons is a reduction reaction
What happens when negative ions are attracted to the anode
They lose electrons to become atoms
- losing electrons is an oxidation reaction
Electrolysis of lead bromide takes place
PbBr2
What are the half equations for each electrode
Br has a negative 2 charge
Pb had a positive 2 charge
Pb ions will go to the electrode and gain 2 electrons to become Pb
Pb —> Pb^2+ + 2e-
Br ions will go to the anode and will lose 2 electrons to become Br atoms
2Br- - 2e- —> Br2
What is electrolysis
- Passing an electric current through a substance
- to break down the substance into elements
List the reactivity series
(Please stop laughing calling me a careless zebra instead try learning how copper saves gold)
Potassium
Sodium
Lithium
Calcium
Magnesium
Aluminum
Carbon
Zinc
Iron
Tin
Lead
Hydrogen
Copper
Silver gold
What are the 2 methods of extracting metals
Reduction using carbon:
- metals that are less reactive than carbon can be extracted using reduction of carbon
- the metal oxide reacts with carbon to produce the metal and carbon dioxide
- the metal oxide is reduced and the carbon is oxidised
Electrolysis:
- if the metal is more reactive than carbon, it can be extracted by electrolysis (expensive and requires lots of energy)
Describe the electrolysis of aluminum oxide (bauxite)
- electrolysis can be used to extract metals from their ore, when the metal is too reactive to be reduced by carbon
- aluminum is extracted from the ore bauxite, which contains aluminum oxide (Al2O3)
1) aluminum oxide has a very high melting point so it’s mixed with cryolite which reduced the melting point.
- the reduced the amount of energy used, reducing costs
2) the molten mixture contains ions free to move, so when we pass a current through the substance, it will conduct electricity
3) the positive Al^3+ ions will be attracted to the cathode and gain 3 electrons to become Al atoms (reduction)
Al3+ + 3e- —> Al
4) the negative O^2- ions will get attracted to the anode where they will lose 2 electrons to become Oxygen atoms (oxidation )
O^2- - 2e- —> O or
O^2- —> O + 2e-
The oxygen atoms will bond to form O2 molecules, so we double the equation
2O^2- —> 2O + 4e-
5) the electrode are made of graphite which is a form of carbon, so the O2 molecules released at the anode will reach with graphite to form carbon dioxide
C + O2 —> CO2
Describe the electrolysis of an aqueous solution (dissolved in water)
- in an aqueous solution, as well as the ions from the ionic compound, there will also be hydrogen H+ ions and hydroxide OH- ions from the water
- this is because water molecules ionise to form these ions
At the cathode:
- if the metal produced at the cathode is more reactive than hydrogen, hydrogen gas will be produced
- if the metal is less reactive than hydrogen, a solid layer of the metal will be produced, coating the cathode
At the anode:
- if halide ions are present, the halogen will be formed
- if no halide ions are present, the OH- ions will be discharged as oxygen gas (and water will be formed)
Describe the elctrolysis of copper sulfate solution
- copper sulfate is written as CuSO4
With the ions Cu^2+ and SO4^2- - along with water, there are additional H+ and OH- ions too
At the cathode:
- the Cu^2+ and H+ ions will be attracted to the cathode. Cu ions will gain 2 electrons to become copper
- because copper is less reactive than hydrogen, it will be produced and coat the cathode with a thin layer
Cu2+ + 2e- —> Cu (reduction)
At the anode:
- the SO4^2- and OH- ions will be attracted to the anode.
- because there are no halide ions present, OH- will discharge as oxygen gas (and produce water)
OH- - e- —> O2 + H2O
Balanced:
4OH- - 4e- —> O2 + 2H2O
Describe the electrolysis of sodium chloride solution
- sodium chloride is written as NaCl with the ions Na+ and Cl-
- because it’s an aqueous solution there are additional H+ and OH- ions too
At the cathode:
- the Na+ and H+ ions are attracted to the negative cathode
- because sodium is more reactive than hydrogen, the H+ ions will gain an electron and hydrogen atoms
H+ + e- —> H
- hydrogen atoms will then bond to form H2 molecules so we double the equation
2H+ + 2e- —> H2 (reduction)
At the anode :
- the Cl- and and OH- will be attracted to the positive anode
- because Cl- ions are halide ions, they will gain an electron to form chlorine atoms
Cl- - e- —> Cl
- the chlorine atoms will pair to form chlorine molecules so we need to double the equation
2Cl- - 2e- —> 2Cl (oxidation)
Uses of electrolysis
- used to electroplate objects
- this can be for appearance, durability or prevention of corrosion
(Copper and silver plating)
