A2 OCR Chemistry: Redox Titrations

Worked example + notes.

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Emi
l
y Summer
s
Redox Titrations
Oxidation
is
loss
of
elect
rons
Reduction
is
gain
of
elect
rons
2+ 3+
Fe (
aq)
Fe (
aq)
+
e
The
Ir
on (
II
)
oxi
dat
ion
stat
e i
s less stable
than
Iron
(I
II
)
so i
n presence
of
air
and
in
the
cont
act
wi
th
anot
her
oxidi
si
ng agent,
Ir
on
(I
I)
i
s r
eadil
y oxi
dised
to
Ir
on (I
II
)
MnO 4 i
s a
str
ong
oxi
disi
ng
agent
and
in
aci
dic
sol
uti
on
it
can
be
reduced
to
2+
Mn
+ 2+
MnO4
(aq)
+
8H (
aq)
+
5e
Mn (
aq)
+
4H2O(l
)
+ 2+ 2+ 3+
MnO4
(aq)
+
8H (
aq)
+
5 Fe
Mn (
aq)
+
5Fe (
aq)
+
4H2O(l
)
2+
MnO4
(pur
ple)
Mn (
pal
e pi
nk/
col
our
less)
Hydrochl
ori
c aci
d cannot
be
used i
n t
it
rat
ions
invol
vi
ng
MnO4a s
they
w i
l
l
react
t
o f
orm
chl
ori
ne,
inst
ead sul
phuri
c aci
d can
be used.
Worked Example
25cm3 of
a
solut
ion
of
Ir
on (
II
)
sal
t
requi
red
23cm3 of
a
0.0200mol
dm3
Pot
assi
um
Mangan at
e (
V I
I)
f
or
comp l
ete
oxi
dat
ion
in
aci
d sol
uti
on
4
n
(MnO4)
=
c x
v
/
1000
= 0.
0200
x 23.
00
/
1000
= 4.
60
x 10 mol
2+ 3
n
(Fe )
= 4.
60
x 104
x 5
= 2.
30
x 10 mol
2+ 3
c
(Fe )
= n/
v x
1000
= 2.
30
x 103/
25.
0 x
1000
= 0.
0920
mol
dm

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