redox
oxygen transfer
oxi: gain o2
reduction: lose o2
fixed os
group 1 and 2 metals= +1,+2
f=-1, h=+1 except metal hydrides
o=-2, h2o2: o=-1
cl=-1 except cl2o:cl=+1
what it does
converts chemical energy to electrical energy w spontaneous redox reactions
link to metal reactivity
more negative means more reactive
how it works
electricity is passed through an electrolyte, chem reactions take place at electrodes, electrical energy to chem energy, cation get e anion give e
electron transfer
oxi: lose e
red: gain e
change in os
os goes up for oxi, down for red
electrode potential
potential difference between metals and its ions at equilibrium
standard cell potential
e nott reduction - e nott oxidation
selective discharge
ease of oxi/red: more positive is red, less positive is oxi
conc of species: ions of higher conc are discharged in preference
nature of electrode: electrode is inert/reactive, if metal electrode is high in electrochemical series, undergo oxi avail anions not discharged
hydrogen transfer
oxi: lose h
red: gain h
oxidising agent
gets reduced
standard cell potential
potential difference betweem 2 half cells under standard cell conditions
spontaneous reaction
> 0 = spontaneous, = 0 = no net redox reaction, < 0 = non spontaneous
laws and eqns
1st: mass/vol of gas liberated at electrode is directly proportional to quantity of electrcity
2nd: quantity of electricity required to discharge 1 mol of element depends on charge of ion
q=i x t
q=96500 x no. of mols of e
h2 = 0, mg = 0, k+ = +1
reducing agent
gets oxidised
she
consists of pt electrode inert to involve equilibrium between h2 gas and ions, arbitrarily assigned a standard cell potential of 0
corrosion of iron
rusting needs o2 and h2o, prevent by coating w protective layer or using more reactive metal
electrolytic purification: impure copper at anode, thin sheet of pure copper at cathode, electrolyte must be aq copper
at anode: more reactive metal dissolves as ions, less reactive falls as sludge
at cathode: copper increases in mass
electroplating: process of depositing a layer of metal on another substance
os in ion/molecule/compound
co2:o=-2, c=+4
tests
oxidising agent: add KI, turn brown
reducing agent: add k2cr2o7, orange to green, add kmno4, purple to colourless
parts and func
electrode: allow movement in and out of cell
anode: oxi
cathod: red
electrolyte: liquid/aq substance w mobile ions to conduct electricity
external wire: conducting wire connecting anode to cathode
salt bridge: maintain electrical neutrality by preventing a build-up of charges
electrolysis
passing an electric current to force a non spontaneous reaction
parts and func lysis
battery: provide e flowing in one direction to cathode, driving force for non spontaneous reaction
electrolyte: molten ionic compound/aq solution that conducts electricity, acts as medium for transport of charged particles
electrodes: conducts electricity, usually metal plates/carbon graphite rods