Definition
Definition
Definition
Definition
Addition of
oxygen OR
removal of
hydrogen
Addition of
hydrogen OR
removal of oxygen
Loss of electrons
OR increase in
oxidation number
Gain of electrons
OR decrease in
oxidation number
oxidation
reduction
oxidation
reduction
GER!!!!
Oxidation number
of an element eg
Zn, O2, S8 or C is
Sum of the
oxidation numbers
in a “molecule” eg
H2O, CH4, NaCl, is
Leo (loss of
electrons oxidation)
Ger (gain of
electrons reduction
zero
zero
Sum of oxidation
numbers in a
polyatomic ion, eg
SO42-, Cr2O72-,
NH4+, is…
Oxidation number
of a simple ion, eg
S2-, Cr3+, Fe3+, is…
The oxidation
number of O in
compounds is…
The oxidation
number of H in
compounds is…
the charge on
that ion
the charge on
that ion
-2 (unless a
peroxide, -1)
+1 (unless metal
hydride, -1)
I AM LEO
The oxidation
number of F in
compounds is…
-1
RIG(e)
OIL(e)
reduction is gain
(of electrons)
oxidation is loss
(of electrons)
Balance atoms – that
are not H or O
Balance O – add water
Balance H – add H+
Balance charge – add eto more positive side
balancing half
equations
Oxidising agent
Oxidising agent
Oxidising agent
Oxidising agent
Acidified orange
dichromate
H+/Cr2O72- is
reduced to
Acidified purple
permanganate H+/
MnO4- is reduced
to
Colourless
hydrogen
peroxide, H2O2 is
reduced to
Very pale orange
iron(III) ion Fe3+
is reduced to
green
chromium(III) ion
Cr3+
“colourless”
manganese ion,
Mn2+
colourless water,
H2 O
very pale green
iron(II) ion Fe2+
Oxidising agent
Oxidising agent
Oxidising agent
Oxidising agent
Pale greeny-yellow
chlorine Cl2 is
reduced to
Orange brown
iodine I2 is
reduced to
Oxygen gas, O2 is
reduced to
Hydrogen ion, H+,
eg from acids like
HCl or H2SO4 is
reduced to
colourless Cl- ion
(& pungent smell
disappears)
colourless I- ion
oxide ion O2-
colourless
hydrogen gas, H2
Reducing agent
Reducing agent
Reducing agent
Reducing agent
Metals, eg Mg, Zn
or Cu are oxidised
to
Black carbon, C, is
oxidised to
Colourless carbon
monoxide gas, CO,
is oxidised to
Colourless
hydrogen gas, H2,
is oxidised to
metal ions, Mg2+,
colourless CO2 gas colourless CO2 gas
Zn2+ or Cu2+
colourless H+ ion
Reducing agent
Reducing agent
Reducing agent
Reducing agent
Very pale green
Colourless
iron(II) ion Fe2+ is bromide ion, Br-, is
oxidised to
oxidised to
Colourless iodide
ion, I-, is oxidised
to
Colourless,
pungent smelling
sulfur dioxide gas,
SO2 is oxidised to
very pale orange
iron(III) ion Fe3+
orange-brown
solution of iodine,
I2 (or grey solid)
reddish brown
bromine, Br2
colourless
sulfate, SO42-
Reducing agent
Increase in
oxidation number
is
Decrease in
oxidation number
is
No change in
oxidation number
eg Cr2O72- 
CrO42-, (Cr +6 in
both) means that
colourless
sulfate, SO42-
oxidation
reduction
it is NOT a
redox reaction
Redox reaction in
which the same
element is both
oxidised and
reduced is called
Oxidising agent is
another name for
an
Reducing agent is
another name for
a
Oxidising agents
_____ electrons
and are _____ in
the process
disproportionation
oxidant
reductant
gain
reduced
Halogens as
oxidants
Halogens as
oxidants
Colourless,
hydrogen sulphite,
HSO3- is oxidised
to
Reducing agents
_____ electrons
and are _____ in
the process
To combine
balanced half
equations x by
factors so that
lose
oxidised
the electrons will
cancel out
Halogens as
oxidants
Halogens as
oxidants
Cl2, Br2 & I2 react
with water H2O to
make
F2 , v. strong
oxidant, reacts
with H2O to make
HCl + HOCl
i.e. HX + HOX
HF + O2
Oxidising strength Will oxidise other
is F > ….
elements eg Fe +
Cl2 forms
Cl > Br > I
FeCl3
Test for chlorine
gas (starch-iodide
paper)
Test for chlorine
gas (moist litmus
paper)
Turns starchiodide paper
black (I2 made)
Turns red and
then is bleached
by HOCl
Halogens as
oxidants
Halogens as
oxidants
Halogens as
oxidants
Halogens as
oxidants
Reaction with
halides
Reaction with
halides
Cl2 + Br- or I-
Br2 + I-
Br2 is not a strong
enough oxidising
agent to oxidise…
I2 is not a strong
enough oxidising
agent to oxidise…
produces Cl- &
Br2 or I2
produces Br- & I2
chloride
chloride or
bromide
Oxidising agents
_______ other
species and in the
process they
become _____
Reducing agents
_______ other
species and in the
process they
become _____
Colour change
Colour change
Mix H+/ MnO4- &
Fe2+
Mix H+/ Cr2O72- &
Fe2+
oxidise
reduced
reduce
oxidised
purple to
colourless (slight
pale orange)
orange to green
Electrolysis
Electrolysis
Electrolysis
Electrolysis
Anions (-) are
Cations (+) are
Electrolyte is ionic
attracted to the
attracted to the
compound that is
positively charged negatively charged either _____ or
electrode, the …
electrode, the …
_____
Oxid
Ation
occurs at the…
anode
cathode
aqueous or molten
anode!
Electrolysis
Electrolysis
Electrolysis
Electrolysis
Redu
Ction
occurs at the…
cathode!
Used to extract
In Al extraction
In Al extraction
aluminium from its the carbon anodes the Al2O3 is mixed
ore, alumina….
have to be
with cryolite to
replaced as they
aluminium oxide
Al2O3
react with O2 to
make CO2 gas
lower the m.pt.
and so save $$$
Electrolysis
is used to
electroplate metal
items which are
made the…
cathode
Electrolysis
Is used to purify
copper by making
an impure ___,
pure ___ and
using CuSO4(aq)
Electrolysis
of
NaCl solution
produces
Electrolysis
of
CuCl2 solution
produces
Cu anode
Cu cathode
H2 & Cl2 (and
NaOH solution)
Cu & Cl2
Electrolysis
Electrolysis
of
molten PbBr2
produces ___ at
cathode and ___
at anode
Electrolysis
If the solution of
NaCl or CuCl2 is
very dilute you will
get ___ instead
of Cl2
ionic compound
must be (aq) or
molten (l) so that
the ions are
Electrolysis
of
molten NaCl
produces ___ at
cathode and ___
at anode
oxygen, O2
free to move
sodium metal
chlorine gas
lead metal
bromine
Electrolysis
___ conduct in
solution / molten
liquid, ___ carry
the charge in the
wire
Oxidation No. /
state of N
in N2O4 is
Electrolysis of
acidified water
Electrolysis of
acidified water
@ anode
@ cathode
2OH– 
O2 + 2H+ + 4e–
2H+ + 2e–  H2
ions
electrons
+4
Other colours to
know… copper(II)
ion Cu2+ is
Nitrogen dioxide
gas, NO2, is
Oxidation No. /
state of N
in NO3- is
Oxidation No. /
state of N
in NH4+ is
blue
brown
+5
-3