C4 - electrochemistry Flashcards
define electrolysis
-decomposition of an ionic compound, when molten or in aqueous solution, by the passage of an electric current
parts of an electrolytic cell
-cell - longer side is positive terminal
-anode - positive electrode
-cathode - negative electrode
-electrolyte - molten/ aqueous substance that undergoes electrolysis
-external circuit: cell
-internal circuit - electrodes, electrolyte
-electrical E to chemical E
what are electrode made out of & why
-graphite/ platinum
-inert so that they aren’t involved in the reaction
-PANCake
Positive Anode, Negative Cathode
electrode & the ion, discharging, electroplating, purifying, hydrogen fuel cell
CAThode - CATion, metal/ hydrogen, object, pure, water
ANode - ANion, non-metals (no hydrogen), metal, impure, hydrogen ions
cathode reduced the pure metal object
direction of electrons & current
-current - ( + ) ( - )
-electron - ( - ) ( + ), anode to cathode
redox reaction
-OIL RIG
-anode - anions gain electrons - oxidation
-cathode - cations lose electrons - reduction
eg. oxidation - 2Pb+ + 2e- ——> 2Pb
reduction - 2Br- ——> Br2 + 2e-
where does electrons & ions move
-electrons - external circuit
-ions - electrolyte
discharging
-Cathode - if jewelry metal (Cu, Ag, Au, Pt, W), metal is produces; else, Hydrogen gas produced
-Anode - if has halide ion, halogen gas is produces; else, oxygen gas produced
-if electrolyte is molten, only 2 types of molecules
-if electrolyte is aqueous, 4 types of molecules
-metals or hydrogen are formed at cathode
-non-metals (other than hydrogen) are formed at anode
reaction of H+ being reduced, OH- being oxidized
-2H+ 2e- —–> H2 (g)
-4OH—–> O2 (g) + 2H2O + 4e-
electroplating
-cathode - object
-anode - metal
purifying metals
-cathode - pure
-anode - impure
purifying copper using copper electrodes
-Copper sulfate as electrolyte
-cathode: pure copper at cathode
-anode: impure copper
-solid copper become ions in solution & goes to cathode
-copper ions in solution go to cathode
-impurities fall
-cannot have a halide in the electrolyte
Simple cell
-electrodes aren’t inert
-cathode - less reactive metal - reduction
-anode - more reactive metal - oxidation - shrink in size
-greater reactivity difference between metals, more Voltage produced
-chemical E to electrical E
hydrogen fuel cell
-uses hydrogen & oxygen to produce electricity & water
-membrane is btw platinum electrodes
-hydrogen & oxygen is pumped in the membrane
-excess hydrogen & water is pumped out
-motor is connected to the electrodes & electrons flow through the external circuit
reactions in a hydrogen fuel cell
-cathode: 4H+(aq) + 4e- + O2(g) → 2H2O(l)
-anode: 2H2(g) → 4H+(aq) + 4e-
-overall: 2H2(g) + O2(g) → 2H2O(l)
advantages of hydrogen fuel cell
-no power lost in transmission as there are less moving parts than an internal combustion engine
-Produces a voltage as long as it’s supplied with hydrogen & oxygen
-only product is water, not a greenhouse gas.
-doesn’t need recharging using mains electricity
-no moving parts
-quieter than a petrol or diesel engine.
-fits into an engine bay.
disadvantages of hydrogen fuel cell
-hydrogen must be stored in the car & is explosive
-hydrogen will run out/need replacing.
-few hydrogen stations for refueling (unlike electrical outlets)
-If the hydrogen is manufactured from coal or natural gas, carbon dioxide is produced
-uses expensive platinum electrodes
note:
-Sodium cannot be used to electroplate using aqueous solution - highly reactive
-overhead cables are made of Aluminum - cheap, low density, better electrical conductor than steel (3 valence e- )
