electrolosis (paper 2) 32, 33 Flashcards
what two processes occur during electrolysis
- oxidation
- reduction
what is meant by the term ‘electrolysis’
the breaking down of a substance using electricty
what is oxidation (in terms of electrons)
loss of electrons
what is reduction (in terms of electrons)
gain of electrons
what is a positive ion called
cation
what is a negative ion called
anion
which electrode do cations (positive ions) go to
the negative electrode
what is the name of the negative electrode which attracts positive ions
cathode
which electrode do anions (negative ions) go to
the positive electrode
what is the name of the positive electrode which attracts negative ions
anode
explain what happens to ions at the electrodes
the ions gain or lose electrons and they form the incharged substance and are discharged from the electrode
what do half equations show
how electrons are transferred during reactions
what must the substance being broken down be able to do
conduct electricity
what is an electrolyte
a liquid containing ions which will conduct electricty
what type of ion would be attracted to the cathode
cations = positive ions = metals / hydrogen
what type of ion would be attracted to the anode
anions = negative ions = non-metals / oxygen
why do ionic compounds have to be molton for electrolysis to work
because when molton, the ions can move
why are electrodes made out of graphite
- not reactive
- has delocalised electrons which can conduct electricity
what is meant by the term redox
when reduction and oxidation happen at the same time in reaction
what process happens at the cathode
reduction
what is the half equation like for the cathode
electrons on the left side (in front of the arrow)
what process happens at the anode
oxidation
what is the half equation like for the anode
electrons on the right side (behind the arrow)
explain how lead(II) ions get seperated from lead bromide
- positive lead2+ ions get attracted to the negative cathode
- the cathode transfers 2 electrons to each lead ion and causes it to sink and collect at the bottom
- this process is reduction as the lead ions gain electrons to become lead atoms
- Pb2+ + 2e- -> Pb
explain how bromide ions get seperated from lead bromide
- negative Br- ions get attracted to the positive anode
- 2 bromide ions loose one electron each and are oxidised to form a bromine molecule
- 2Br- -> Br2 + 2e-
what is a hoffmann voltammeter
the name of the electroysis aparutus
describe how to set up an electrochemical cell
- get two inert electrodes (graphite or platinum)
- clean the surfaces of electrodes with sand paper ~ do not touch surface from now ~ grease
- place both electrodes into beaker filled with electrolyte
- connect eletrodes to power supply with crocodile clips and wires
- turn power supply on and a current will flow through the cell
what is the difference of electrolysis of a pure solution vs an aqueous solution
hydrogen ions and hydroxide ions will also form from the water
what forms at the cathode (-ve) for an aqueous solution
- if the metal is copper or silver they will form
- if not then hydrogen forms
what forms at the anode (+ve) for an aqueous solution
- if negative ion is a halide it will form
- if not (eg, SO4, CO3, NO3) then oxygen gas forms from OH-
what is the half equation for the formation of oxygen gas from hydroxide ions at the anode when an aqueous solution is seperative and the anion is not a halide
4OH- -> O2 + 2H2O + 4e-
