Iodimetry & iodometry

all about iodometry and iodimetry. differences

1. IODOMETRY & IODIMETRY Iodometric titration is always performed in neutral or weak acid or weak basic solution . Prepared by- Apusi chowdhury Roll no. : 898

2. Iodometry

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 (K 2 Cr 2 O 7 ) and KI (excess) Thus the iodine is quickly liberated. KI + Oxidizing agent → I 2  K 2 Cr 2 O 7  + 6KI + 7H 2 SO 4   → Cr 2  (SO 4 ) 3  + 4K 2  SO 4  + 7H 2 O + 3I 2

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. I 2  + 2 S 2 O 3 2−  → S 4 O 6 2−  + 2I -

6. Iodimetry

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 KI 3  solution is prepared. KI+I 2  → KI 3 Starch can be used as an indicator in iodimetric titrations too. I 2  + 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 :- I 2 +H 3 AsO 3 +H 2 O  H 3 AsO 4 +2I - +2H + The pH of iodine solution should be < 8.5 because iodine disproportionate at basic pH. Strong alkali such as NaOH or Na 2 CO 3 cannot be used for this purpose, because they react with iodine to form various oxyhalogen compounds. I 2 + 2OH -  I - +IO - H 2 O 3IO -  2I - + IO 3 - ( 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 - + O 2 + 4H +  2I 2 +2H 2 O The reaction tend to go from right to left . T hiosulphate decompose to S 2 . 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

11. Conclusion

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].

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