electrolysis Flashcards
(21 cards)
why is cryolite used?
to lower the melting point, reducing energy used and cost
why is electrolysis expensive?
it requires a lot of energy
describe what happens to the Al₃ ions in electrolysis of Al₃O₂
the positive ions are attracted to the negative electrode where they each gain 3 electrons to turn in Al atoms, these sink to the bottom of the tank
describe what happens to the O₂ ions in electrolysis of Al₃O₂
the negative ions are attracted to the positive anode where they each lose 2 electrodes, the neutral oxygen atoms with combine to form O₂ molecules
what are the electrodes made of?
carbon (graphite)
why are the electrodes made of graphite?
it conducts electricity
why does the positive electrode need to be regularly replaced?
it reacts with oxygen to produce carbon dioxide
half equation at the cathode for Al₃O₂
Al³⁺ + 3e⁻ -> Al
half equation at the anode for Al₃O₂
2O²⁻ -> O₂ + 4e⁻
are the elements oxidised or reduced at the cathode?
reduced
what other ions are present in water?
hydrogen and hydroxide
PANIC
positive anode
negative is cathode
rule at cathode for aqueous solutions
if the metal is more reactive than hydrogen, hydrogen gas is produced
the solid metal is produced if it is less reactive
rule at anode for aqueous solutions
if there is a halide or oxygen present, then that gas will be produced, OH⁻ ions are discharged forming oxygen gas and water molecules
what is produced when copper sulfate solution is electrolysed?
copper metal is produced at the cathode
oxygen and water are produced at the anode
what is produced when sodium chloride solution is electrolysed?
hydrogen gas at the cathode
chlorine gas at the anode
variables
independent-solution
dependent-elements produced
control-electrodes
half equation at anode for copper sulfate solution
4OH- -> 2H2O + O2 + 4e-
electrolyte
a solution able to conduct electricity that contains a molten or dissolved ionic compound
why does the aqueous rules happen?
- because in the aqueous solution water molecules break down producing hydrogen ions and hydroxide ions that are discharged
explain how oxygen gas is produced in the electrolysis of sodium sulfate solution
- water breaks down into H+ and OH- ions
- OH- is attracted to anode
- because opposite charges attract
- no halide present
- so OH- ions will oxidise at the anode
- releasing water and oxygen gas
