all about iodometry and iodimetry. differences

1. Prepared by-
Apusi chowdhury
Roll no. : 898

3. • the quantitative analysis of a solution of an
oxidizing agent by adding an iodide which
reacts to form iodine.
• The released iodine is then titrated with
another species.
• Usually, a standard thiosulphate solution is
used for this. the method is called
"iodometry".
Reference: Chatten, L. (1966). Pharmaceutical chemistry. 2nd ed. New York: Dekker, pp.151, 152.

4. The first step is done by the reaction between the oxidizing
agents (K2Cr2O7) and KI (excess) Thus the iodine is quickly
liberated.
KI + Oxidizing agent → I2
K2Cr2O7 + 6KI + 7H2SO4 → Cr2 (SO4)3 + 4K2 SO4 + 7H2O + 3I2

5. The liberated iodine
(in first step) is titrated
with standard solution
of sodium thiosulfate.
Starch is used as
indicator. At the end
point, the blue or violet
color of starch
indicator disappears.
I2 + 2 S2O3
2− → S4O6
2− + 2I-

7. • When an analyte that is a reducing agent
is titrated directly with a standard iodine
solution, the method is called "iodimetry".
• Iodine is mixed with potassium iodide
and KI3 solution is prepared.
KI+I2 → KI3
• Starch can be used as an indicator in
iodimetric titrations too.
I2 + reducing agent → 2 I-
Reference: Chatten, L. (1966). Pharmaceutical chemistry. 2nd ed. New York: Dekker, pp.151.

8. Iodometric titration cannot be
performed in strong basic solution
or strong acid solution.

9. consider a reaction :-
I2 +H3AsO3 +H2O H3AsO4 +2I- +2H+
• The pH of iodine solution should be < 8.5 because
iodine disproportionate at basic pH.
• Strong alkali such as NaOH or Na2CO3 cannot be
used for this purpose, because they react with
iodine to form various oxyhalogen compounds.
I2 + 2OH-  I- +IO- H2O
3IO-  2I- + IO3
-
(iodate)
Reference: Chatten, L. (1966). Pharmaceutical chemistry. 2nd ed. New York: Dekker, pp.151.

10. • In acidic media, the iodide ion tends to get
oxidized.
4I- + O2 + 4H+  2I2 +2H2O
• The reaction tend to go from right to left.
• Thiosulphate decompose to S2.
• If the solution is strong acid, when using starch
as indicator at the end point, it is either
decomposed or hydrolyzed.
Reference: Chatten, L. (1966). Pharmaceutical chemistry. 2nd ed. New York: Dekker, pp.152

12. • Iodine is very useful in titration method,
• These methods are used to determine the
concentration of vitamin-C, sodium
thiosulphate, amount of copper in super
conductor etc.
• Determining the concentration of these
chemicals is important because
hydroperoxides have a negative effect on
the acceptability of the fat matrix used
Reference: Mendham, J.; Denney, R. C.; Barnes, J. D.; Thomas, M. J. K. (2000), Vogel's Quantitative
Chemical Analysis (6th ed.), New York: Prentice Hall.. Navigilo, d. (2016). Iodometry and Iodimetry, PP 265

13. •
Reference :-
Mendham, J.; Denney, R. C.; Barnes, J. D.; Thomas, M. J. K.
(2000), Vogel's Quantitative Chemical Analysis (6th ed.),
New York: Prentice Hall.
Navigilo, d. (2016). Iodometry and Iodimetry, PP 265.
Daniele Naviglio .Analytical Chemistry .Agraria .Federica e-
Learning. [online] Federica.unina.it.
Available at:
http://www.federica.unina.it/agraria/analytical-
chemistry/iodometry/ [Accessed 7 Nov. 2016].