Redox titrations just as an acid can be used to find

Redox Titrations
Just as an acid can be used to find the concentration of a base (or
vice versa) in an acid-base titration, a known concentration of an
oxidising agent can be used to find the unknown concentration of a
reducing agent (or vice versa).
When dissolved in ethanol, polyiodide salts, NMe
4
.I(I
2
)
x
or
NMe
4
.I
2x+1
, are a source of 'free' iodine as in the equation:
NMe
4
.I(I
2
)
x
→ NMe
4
+ + I - + xI
2
An iodine / thiosulfate redox titration can be employed to determine
the amount of I
2
released. The chemical equation for the iodine /
thiosulfate titration is:

I
2
+ 2S
2
O
3
2-
→ S
4
O
6
2-
+ 2I
-
1. 1.
-
The oxidising agent in the titration is
I
2
Correct!
HintExplanation
2. 2.
-
The indicator used in this titration is
starch
Correct!
HintExplanation
3. 3.
-

The colour change indicating the end-point of the titration is from
blue to colourless
Correct!
HintExplanation
Using Titration Data
In a redox analysis of a polyiodide salt by titration of the liberated
iodine with shiosulfate, titration of 20.00 mL aliquots of a solution
of the polyiodide salt (initial volume 100.0 mL) containing
elemental iodine, yielded an average titre of 21.15 mL of 0.02000 M
thiosulfate solution.
NMe
4
.I(I
2
)
x
→ NMe
4
+ + I - + xI
2
I
2
+ 2S
2
O
3
2-
→ S
4
O
6
2-
+ 2I
-
1.