electrolysis Flashcards
what does electrolysis look at?
the use of electrical energy to make chemical energy (ie chemicals)
what is electrolysis used in?
recharging batteries
industrial production of chemicals
electroplating
how is the ECST interpreted?
non-spontaneous uphill gradient
shortest gradient
discharging
chemical to electrical
recharging
electrical to chemical
electrolyte can be:
molten, aqueous
if molten:
no water, proceed to ECST and ignore water
if aqueous:
water needs to be considered
greater than 5M:
lots of ions, less water, water cannot be both oxidant and reductant
less that 5M:
less ions, more water, water can be both oxidant and reductant
how to predict products at electrodes
identify all species
circle on ECST
determine shortest uphill gradient
down cell
- molten NaCl
- force electrons into non-spontaneous reaction
membrane cell
- selectively permeable for Na+
- 5M brine
- must consider if water can react
- must consider the fact Na has been selected for and therefore cannot react until end when it might help form product
hall harolt cell
alumina in cryolite to keep temp down to keep alumina molten (cheaper)
anodes are carbon
electrons forced through pick up aluminium ions and form aluminium which flows out
oxide ions react with c at anode and carbon dioxide is produced
electroplating
the coating of an object with a metal
how does an electroplating cell work?
galvanic anode forces electrons into electrolytic cathode (object)
galvanic cathode attached to electrolytic anode which breaks off to form ions to replenish electrolyte
ions join with electrons on object to become a coating
electrolyte must contain ions that eventually undergo reduction to coat
inert electrode
the ions are not replenished and the chemist needs to control this
stoich in electroplating
charge is the same as number of electrons
what does charge govern?
the mole of electrons required for the metal being deposited
anode
positive
cathode
negative
what is faraday’s study?
the relationship between electrical charge and mass deposited at cathode
faradays equations?
Q = I x t Q= coloumbs I= amps t= time seconds
Q = n(e-) x faradays constant
96500Cmol-1
primary cell
batteries that cannot be recharge such as galvanic cells- button cell
secondary cell
batteries that are rechargeable- operate as both electrochemical and electrolytic cells- phone
chemical energy to electrical
discharging, galvanic cell, energy is made
electrical to chemical
recharging, electrolytic, energy is required
