electrolysis ! Flashcards
electrolysis !
conduction of electricity by an ionic compound (electrolyte) when molten or dissolved in water, leading to the decomposition of the electrolyte
parts of electrolytic cell !
electrode
anode
cathode
battery
electrolyte !
ionic compound
when in molten state : mobile ions conduct electricity
electrode !
electrical conductor (carbon, graphite)
connected to positive & negative terminals of battery
anode !
positive electrode : connected to positive terminal of battery
electrons leave electrolyte
oxidation occurs : lose electrons
cathode !
negative electrode : connected to negative terminal of battery
electrons enter electrolyte
reduction occurs : gain electrons
battery !
elects pump : draws electrons away from anode
- electrons : enter positive terminal of battery & pumped out at negative terminal
external circuit !
conducts electricity due to flow of electrons
factors affecting selective discharge of ions !
position of metal / ion in reactivity series
- selective discharge of cations at cathode
- selective discharge of anions at anode
concentration of selective discharge at anions
nature of electrode
selective discharge of cations at cathode
metal/hydrogen : formed at cathode
ions of more reactive metals : remain in solution as ions -> not discharged as they are more stable as ions
ions of less reactive metals : preferentially discharged -> reduced back to metal as they are less stable in solution
selective discharge of anions at anode !
non-metals (excluding H) : formed at anode
ions higher in series : remain in solution as they are more stable in solution
ions lower in series : preferentially discharged as they are less stable in solution
cathode reactive series !
SO4 2- NO3- CL- BR- I- OH-
concentration of selective discharge of anions !
high concentration of ion : more readily discharged
nature of electrode !
product of electrolysis : differ when diff electrodes are used
- eg : inert -> carbon, platinum
applications of electrolysis !
electrolytic purification of copper
electroplating
electrolytic purification of copper !
anode : impure copper
- Cu (s) -> Cu2+ (aq) + 2e-
cathode : pure copper
- Cu2+ (a1) +2e- -> Cu (s)
circuit closed : pure copper from anode dissolves -> form Cu2+ ions -> move over to cathode
impurities (silver,platinum) : fall to bottom of anode
mass of anode decreases, mass of cathode increases
electroplating !
process of depositing a layer of metal on another substance by electrolysis
anode : source of plating metal
cathode : object to be electroplated
electrolyte : aq solution of a salt of the plating metal
electroplating uses !
prevent objects from corrosion
give the object a shiny/attractive appearance
electroplating conditions !
metal object to be plated : must be clear & free of grease
concentration of metal ions : must be low
electric current : must not be too large
- coating layer will form too rapidly & peel off easily
simple cells !
device that converts chemical energy into electrical energy
made by placing 2 diff metals which act as the electrodes in contact with an electrolyte
anode : more reactive metal -> gives up electrons to form ions -> oxidation occurs
cathode : less reactive metal -> ions in solution gains electrons -> reduction occurs
electron flow from more reactive metal (anode) to the less reactive metal (cathode)
simple cells & reactivity series !
the further apart the 2 metals are in the reactivity series, the greater the outage produced in the cell
no current flow if electrodes are made up of the same metal
simple cell vs electrolytic cell !
simple cell
- opp of electrolytic cell in terms of energy conversions
- converts chemical energy -> electrical energy
- produce electricity
electrolytic cell
- converts electrical energy -> chemical energy
- uses electricity
similarity : both are electrochemical cells
advantages of using hydrogen as fuel!
does not cause pollution : product of combustion of water
renewable source of energy : source of H is the electrolysis of water
efficient source of energy : releases twice the amt of energy compared to other fuels
disadvantages of using hydrogen as fuel !
no cheap source of hydrogen : obtaining it from electrolysis is expensive
extremely flammable & explosive : special care & precaution required
is a gas & very light : requires larger storage volume compared to other fuels
