2(i) Electrolysis Flashcards
Electrolysis of Molten Lead Bromide
Positive Electrode:
2Br- -> Br2 + 2e- OXIDATION
Negative Electrode:
Pb2+ + 2e- -> Pb REDUCTION
Electrolysis of Sodium Chloride
Positive Electrode:
2Cl- -> Cl2
Negative Electrode:
2H+ -> H2
- Leaves NaOH
Electrolysis of Copper (II) Sulfate
Positive Electrode:
2O2- -> O2 + 4e-
Negative Electrode:
Cu2+ + 2e- -> Cu
Electrolysis of Dilute Sulfuric Acid
Positive Electrode:
4OH- -> O2 + H2O + 4e-
Negative Electrode:
2H+ + 2e- -> H2
- Ratio of H2: O2 = 2:1
Electrolysis Rules
At positive electrode:
* Halide ions are discharged, otherwise O2
At negative electrode:
* H+ ions are discharged, unless metal is less reactive than hydrogen
The products of an electrolysed aqueous solution are not always the same as the products of electrolysed molten salt
Quantitive electrolysis via mass change/volume of gas produced: Copper Sulfate
With graphite (inert) electrodes: Cu + O2
With copper electrodes:
1. Electrodes are rubbed with emery cloth to remove corrosion (for a fresh layer)
- At positive electrode: Cu -> Cu2+ + 2e-
At negative electrode: Cu2+ + 2e- -> Cu - Dip electrodes in ethanol to help the electrodes faster
Quantitive electrolysis via mass change/volume of gas produced: Gases
Use gas syringe
Quantitive electrolysis via mass change/volume of gas produced: Gases
Use gas syringe
Quantitive Electrolysis: Current and Mass made
Directly proportional
Extracting aluminium through electrolysis: Electrodes
Positive Electrode (top) : Graphite
Negative Electrode (bottom) : Graphite
Cryolite
Used to lower boiling point of aluminium oxide (Al2O3)
Extracting aluminium through electrolysis: Electrodes reactions
Positive Electrode:
2O2- -> O2 -> 4e-
O2 reacts with carbon electrodes to form CO2 (electrodes have to be eventually replaced)
Negative Electrode:
Al3+ + 3e- -> Al (l)
Disadvantage of extracting aluminium
Expensive - requires lots of electricity to make it molten to extract it
