OXIDATION REDUCTION_YEAR_12_CHEMISTRY_STAGE_3
OIXDATION(AND(REDUCTION(–(REDOX(CHEM(1(
(
KEY(REDOX(CONCEPTS(
•! Oxidation)and)reduction)are)electron(transfer(processes)(reactions).)) o! Oxidation(–(Loss)of)electrons))
!! Reductant((reducing)agent))–)undergoes)oxidation.)) o! Reduction(–(Gain)of)electrons))
!! Oxidant((oxidising)agent))–)undergoes)reduction.))
!
Example:(((((((((((Mg(s)(+(2H+(aq)( (Mg2+(aq)(+(H2(g)( o! This!reaction!can!be!broken!up!into!two!halfEreactions((
!! Oxidation:)Mg(s))")Mg2+)+)2e:)(lost)electrons))(
!! Reduction:)2H+)+)2e:)")H2)(gained)electrons))(
Example(at(Molecular(level((
!
A!piece!of!zinc!is!placed!in!a!solution!of!
copper(II)!sulfate,!the!zinc!undergoes! oxidation!and!transfers!electrons!to!the! copper(ions(that(are(then(reduced(to( metallic(copper.!!! !Zn(s)!+!Cu2+(aq)!→!Zn2+(aq)!+!Cu(s)!!
!
(
(
STANDARD(REDUCTION(POTENTIALS((
•! Different)oxidants)and)reductions)have)varying)levels)of)“strength”)and)this) ultimately)determines)if)a)reaction)will)take)place.)) •! There)are)two(basic(rules(that)define)this)concept:))
1.! Metals(s)(will(displace)(and)thus)react))metal(ions(above.))
!! E.g.)Cu(s))will)displace)Ag+(aq)))
2.! Halogens(g)(will(displace)(and)thus)react))halogen(ions(below.))
!! E.g.)F2(g))will)displace)Br:(aq))
Note!2!Positive!ions!of!metals!that!are!strong!reductants!are!themselves!weak!
oxidants.!
•! Subsequently,!the!positive!ions!of!the!metals!that!are!weak!reductants! are!quite!strong!oxidants.( (
Table!summarising!the!relative!strengths!
of!some!strong/weak!oxidants!(gain)!and! reductants(lose).!! !
I!e.!Mg(s)!loses!e2!easily,!and!accordingly!
its!ion!Mg2+!does!not!gain!e2!easily.!!
(
OIXDATION(AND(REDUCTION(–(REDOX(CHEM(1(
(
OXIDATION(NUMBER((ON)((
•! Oxidation(number(A(number)that)is)assigned)to)each)atom)in)a)substance)to) indicate)its)oxidation)state) o! This)is)used)when)it)is)difficult)to)follow)the)transfer)of)electrons,)such) as)in)substances)with)covalent)bonds.)) !
The(rules(for(assigning(oxidation(numbers:((
1.!
(
KEY(REDOX(CONCEPTS(
•! Oxidation)and)reduction)are)electron(transfer(processes)(reactions).)) o! Oxidation(–(Loss)of)electrons))
!! Reductant((reducing)agent))–)undergoes)oxidation.)) o! Reduction(–(Gain)of)electrons))
!! Oxidant((oxidising)agent))–)undergoes)reduction.))
!
Example:(((((((((((Mg(s)(+(2H+(aq)( (Mg2+(aq)(+(H2(g)( o! This!reaction!can!be!broken!up!into!two!halfEreactions((
!! Oxidation:)Mg(s))")Mg2+)+)2e:)(lost)electrons))(
!! Reduction:)2H+)+)2e:)")H2)(gained)electrons))(
Example(at(Molecular(level((
!
A!piece!of!zinc!is!placed!in!a!solution!of!
copper(II)!sulfate,!the!zinc!undergoes! oxidation!and!transfers!electrons!to!the! copper(ions(that(are(then(reduced(to( metallic(copper.!!! !Zn(s)!+!Cu2+(aq)!→!Zn2+(aq)!+!Cu(s)!!
!
(
(
STANDARD(REDUCTION(POTENTIALS((
•! Different)oxidants)and)reductions)have)varying)levels)of)“strength”)and)this) ultimately)determines)if)a)reaction)will)take)place.)) •! There)are)two(basic(rules(that)define)this)concept:))
1.! Metals(s)(will(displace)(and)thus)react))metal(ions(above.))
!! E.g.)Cu(s))will)displace)Ag+(aq)))
2.! Halogens(g)(will(displace)(and)thus)react))halogen(ions(below.))
!! E.g.)F2(g))will)displace)Br:(aq))
Note!2!Positive!ions!of!metals!that!are!strong!reductants!are!themselves!weak!
oxidants.!
•! Subsequently,!the!positive!ions!of!the!metals!that!are!weak!reductants! are!quite!strong!oxidants.( (
Table!summarising!the!relative!strengths!
of!some!strong/weak!oxidants!(gain)!and! reductants(lose).!! !
I!e.!Mg(s)!loses!e2!easily,!and!accordingly!
its!ion!Mg2+!does!not!gain!e2!easily.!!
(
OIXDATION(AND(REDUCTION(–(REDOX(CHEM(1(
(
OXIDATION(NUMBER((ON)((
•! Oxidation(number(A(number)that)is)assigned)to)each)atom)in)a)substance)to) indicate)its)oxidation)state) o! This)is)used)when)it)is)difficult)to)follow)the)transfer)of)electrons,)such) as)in)substances)with)covalent)bonds.)) !
The(rules(for(assigning(oxidation(numbers:((
1.!