Pharmaceutical Analysis (BP102T) � UNIT IV�Redox titrations

Redox titrations
(A) Concepts of oxidation and reduction

B) Preparation and standardization of Potassium Permanganate I. P.,
Ceric Ammonium Sulphate I. P./B. P. and Sodium Thiosulphate I. P./B. P

(C) Types of redox titrations (Principles and applications)
Cerimetry,
Iodimetry,
Iodometry,
Bromatometry,
Dichrometry,
Titration with potassium iodate

1. Prof. Amol . S. Dighe Department of pharmaceutical Chemistry Pravara Rural College of Pharmacy, Loni Pharmaceutical Analysis (BP102T) UNIT IV Redox titrations

2. UNIT-IV Redox titrations (A) Concepts of oxidation and reduction B) Preparation and standardization of Potassium Permanganate I. P., Ceric Ammonium Sulphate I. P./B. P. and Sodium Thiosulphate I. P./B. P (C) Types of redox titrations (Principles and applications) Cerimetry, Iodimetry, Iodometry, Bromatometry, Dichrometry, Titration with potassium iodate

3. Oxidation reduction reaction is a process of electron transfer from one element to another result in change in the valency of reacting ions. Concept of Oxidation and Reduction : Oxidation reduction reaction are the chemical processes in which change in the valency of reacting elements or ions takes place. Oxidation: Oxidation can be defined as, addition of oxygen or removal of hydrogen or loss of electron and in summary increase in the ratio of electronegative to electropositive portion of molecule and is explained with examples as follows: A) Addition of oxygen: when in a compound the oxygen get added due to reaction , it is referred as oxidation B) Removal of hydrogen: In certain compounds oxidation can be referred as removal of hydrogen.

4. C) Increase in the ration of electronegative to electropositive portion of molecule. D) Loss of electron : in a course of reaction, when it leads to loss of electron , it is referred as oxidation. Positive charge represent electron deficiency. Oxidizing agents: An oxidizing agents a reagent that oxidize other substances leading to increase in the oxidation state of the substance by making it lose electrons. Example of oxidizing agents are halogens ( such as chlorine and fluorine ) , oxygen anf hydrogen peroxide.

5. Reduction: Reduction can be defined as process of gain of electron or addition of hydrogen or removal of oxygen and in summary increase in the ratio electropositive to electronegative portion of molecule and is explained with example as follows. A) addition of hydrogen: When in a compound the hydrogen gets added due to reaction, it is referred as reduction B) removal of oxygen: when in a compound the oxygen is removed due to reaction, it is referred as reduction. C) increase in the ration of electropositive to electronegative portion of molecule. D) Gain of electron: In a course of reaction, when it leads to gain of electron, it id referred as reduction

6. FAQ: Define oxidation & reduction reaction with example. Sulphuric acid used in redox titration, give reason. Write a short note on principle involved in redox titration with examples. Discuss the principle and application of redox titration. Discuss the principle of oxidation-reduction titration. Describe in detail the modern concept of redox titration. Explain its various types. Write short note on permanganate titration.

7. Redox titration is a type of titration based on a redox reaction between the analyte and titrant. It may involve the use of a redox indicator and /or a potentiometer. The main redox titration types are Redox titration Titrant Iodimetry Iodine (I2) Bromatometry Bromine (Br2) cerimetry Cerium salts permanganometry Potassium permanganate dichrometry Potassium dichromate

8. Potassium permanganate titration: In this type of titration potassium permanganate used as strong oxiding agents. Principle: Standardization of potassium permanganate is based on redox titration. Here potassium permanganate acts as oxidizing agent in presence of sulphuric acid. It oxidize oxalic acid to carbon dioxide and water and itself it get reduced to potassium sulphate and manganese sulphate. Here potassium permanganate it self act as an indicator which gives end point as colorless to pink. Preparation of 0.02M potassium permanganate . Weight accurately about 3.2 gm of potassium permanganate dissolve it in sufficient quantity of water to produce 1000 ml. Prepare the solution two day before and filter through glass wool if necessary.

9. Standardization of 0.02M potassium permanganate . Weight accurately about 0.1 gm of oxalic acid dissolve it in 80 ml of water . Add 5 ml of conc. Sulphuric acid Warm above solution to nearly 70 0c and titrate with the potassium permanganate solution till a permanent pink color produced. Reaction: Factor: Each ml of 0.02 M potassium permanganate is equivalent to 0.006302 gm of C2H2O4

10. Ceriometry or Cerimetric titration : FAQ: Add note on ceriometry. Ceric ammonium sulphate titration are termed as cerimetric titration. Here ceric ammonium sulphate is used as oxidizing agent acidic condition only in neutral solution ceric hydroxide or basic salts get precipitated. Principle: Standardization of ceric ammonium sulphate is based on oxidation reduction type of titration. Here ceric ammonium sulphate acts as oxidizing agent which oxidizes arsenous acid to arsenic acid and itself get reduced from ceric to cerium. This reaction is very slow at room temperature, therefore osmic acid is used as catalyst. Sodium hydroxide is used to dissolve arsenic trioxide. Here ferroin sulphate solution is used as an indicator which gives the end point from pink to pale blue.

11. Preparation of 0.1 M ceric ammonium sulphate : Dissolve 65 gm of ceric ammonium sulphate with gentle heat in a mixture of 30 ml of sulphuric acid and 500 ml of water. The mixture was cooled and filtered. The resulting solution was diluted to 1000 ml with water. Standardization of 0.1M ceric ammonium sulphate : Weight accurately about 0.2 gm of arsenic trioxide and dissolve it in about 25 ml of 8 % w/v solution of sodium hydroxide and add 100 ml of water. To the above flask add 30 ml of dilute sulphuric acid and 0.15 ml osmic acid solution. Add 0.1 ml of ferroin sulphate solution as an indicator and titrate against ceric ammonium sulphate until color changes from pink to pale blue Factor: Each ml of 0.1 M ceric ammonium sulphate is equivalent to 0.004946 gm of AS23

12. Iodine titration : IMP FAQ: Difference between iodimetric and iodometric titration. Discuss the condition for iodometric titration. Starch solution is added near the end point in assay of iodine. Explain. Difference between iodimetric and iodometric titration. Explain importance of PH condition for each of them. Starch indicator give blue color with iodine, justify it. Discuss the principle and application of iodometry. Write a short note iodimetry and iodometry. Iodine is a moderately weak oxidizing agents, it is reduced to form the iodide anion, as follows. The above redox reaction is completely reversible, and so the iodide anion is a moderately weak reducing agent that will react with oxidizing analytes to produce iodine.

13. Titration involving iodine have evolved for the analysis of a number of oxidizing and reducing agents. In iodimetric titration, the analyzed ( a reducing agent ) react with iodine : iodimetry Where Aox and Ared are the oxidized and reduced forms, respectively of the analyte. In iodometric titration, the analyzed ( a oxidizing agent ) react with an unmeasured excess of iodide to produce iodine. Iodine titration can be carried out b to methods one is iodimetry and the other is iodometry.

14. A) Iodimetric titration: Principle: Iodimetric titration involves the titration with a standard solution of iodine. In this type of titration iodine gets reduced to two corresponding iodide. In Iodimetric types of titration the formation of iodine takes place as result of hydroiodic acid with an oxidizing agent. This is obtained in the reaction flask itself by the action of dilute hydrochloric acid or sulphuric acid with potassium iodide. Conditions/criteria for Iodimetric titration: Iodine is volatile titration is conducted in cold condition as the rise in temperature lead to decrease sensitivity towards starch suspension as an indicator. In strong alkaline solution iodine tends to form its corresponding hypoiodide, hence one must maintain perfectly neutral condition in case of iodine metric titration. As iodine is not soluble in water to solubilize it an excess amount of potassium iodide must be used while preparation the iodine solution. Rate of reaction between the oxidizing agent and the iodine is too slow and hence sufficient time could should be given for the reaction to complete.

15. Preparation of 0.05 M iodine solution : Weight accurately 14 gm of iodine and transfer to a beaker containing 36 gm of potassium iodide in 500 ml water and stir. Add 2 drop of dil HCl and make up volume up to 1000 ml with water. standardization of 0.05 M iodine solution : Weigh accurately about 0.15 gm of arsenic trioxide previously dried at 105 0c for 1 hour. Transfer in 250 ml of conical flask. Dissolve it in 20 ml of 1M NaOH solution by warming if necessary. Dilute with 40 ml of water add 2 drop of methyl orange solution and acidify by adding dil HCl until yellow color change to pink. Add 2 gm of sodium carbonate dilute with 50 ml of water. Titrate slowly with iodine solution using starch as an indicator, until a permanent blue color is obtained. Reaction: Factor: each ml of 0.05 M iodine is equivalent to 0.004946 gm of As2O3

16. B) Iodometry Titration : Iodometry, also known as iodometric titration. It is redox titration where the appearance or disappearance of elementary iodine during reaction indicates the end point. It is to be noted specifically that iodometry involves indirect titration of iodine. Principle: Standardization of sodium thiosulphate is based on redox ( iodometry) type of titration. Here sodium thiosulphate acts as reducing agent. It reduce liberated iodine to iodide and itself get oxidized to sodium tetrathionate. Here potassium iodide anf hydrochloric acid react to generate hydrogen iodide. This hydrogen iodide react with potassium bromated and release iodine. This liberated iodine is then titrated with sodium thiosulphate using starch solution as an indicator. Preparation of 0.1 m sodium thiosulphate : Dissolve 25 gm of sodium thiosulphate , add 0.2 gm of sodium carbonate in carbon dioxide free water and dilute to 1000 ml with the same solvent.

17. Standardization of 0.1 m sodium thiosulphate : Dissolve 0.2 gm of potassium bromate in sufficient water to produce 250 ml To 50 ml of this solution, add 2 gm of potassium iodide and 3 ml of 2M hydrochloric acid and titrated with the same sodium thiosulphate solution using starch solution as an indicator, added toward the end point of the titration. Reaction: Factor: Each ml of 0.1 M sodium thiosulphate is equivalent to 0.002784 gm KBrO3

18. Difference between Iodimerty and Iodometry Iodimerty Iodometry Direct iodine solution is used as titrant Released iodine solution is used as an analyte Starch suspension as an indicator is added at start of titration. Starch suspension as an indicator is added toward the end point of titration The end point of titration is colorless to blue. The end point of titration is blue to colorless For this titration to occur one must maintain neutral condition/PH For this titration to occur one must maintain acidic condition/PH e.g. standardization of 0.05M Iodine Assay of Ascorbic acid e.g. standardization of 0.1M sodium thiosulphate Assay of copper sulphate

19. Potassium dichromate titration: These are the titration which involve use of Potassium dichromate solution as an oxidizing agent acidic condition In this case dichromate ion gets converted into trivalent chromium ion. It has several advantage over potassium permanganate. Potassium dichromate is available in vary pure form. Potassium dichromate is stable over a long period of time and does not get affected by light or heat. Potassium dichromate is sufficient stable provided that they are stored properly. Principle: Standardization of Potassium dichromate is based on oxidation reduction iodometric type of titration. Here Potassium dichromate reacts with potassium iodide to iodine and itself get reduced to chromium chloride and potassium chloride. Starch is used as an indicator which is added to be the endpoint of titration giving the endpoint as blue to light green.

20. Preparation of 0.0167 M potassium dichromate solution: Weight accurately about 4.9 gm of potassium dichromate previously powdered and dried in desiccators for 4 hours and dissolved in water to produce 1000 ml Standardization of 0.0167 M potassium dichromate solution: To the 20 ml buffer solution add 1 gm of potassium iodide and 7 ml of 2M hydrochloric acid add to 50 ml of water to the above solution and titrate with 0.1 M Sodium thiosulphate solution using 3 ml of starch solution as an indicator until the color changes from blue to light green. Factor: Each ml of 0.1 M sodium thiosulphate is equivalent to 0.0049 gm og K2Cr2O7

21. Potassium Iodate titration : Potassium iodate can also be used as oxidizing agent for the estimation of iodides, arsenical and other reducing agents. Principle: Standardization of Potassium Iodate is based on oxidation reduction type of titration. Here Potassium iodate react with potassium iodate in the presence of sulphuric acid this lead to liberate iodine. Iodine act as oxidizing agent which oxidizes sodium thiosulphate to sodium tetrathionate. Preparation of 0.05M potassium iodate : Weigh accurately 10.7 gm of potassium iodate transfer in a volumetric flask and add sufficient water produce 1000 ml. Standardization of 0.05M potassium iodate : Dilute 25ml of potassium iodate solution to 100 ml with water. To 25 ml of this solution add 2 gm of potassium iodide and 1M Sulphuric acid and titrate with 0.05M sodium thiosulphate using starch solution as an indicator added towards the end point. Factor: 1 ml of 0.05M Sodium thiosulphate is equivalent to 0.000178 gm of KIO3

22. Bromatometry ( potassium bromate titration) Potassium bromate alone can be used for the analysis of organoarsenicals. The organoarsenicals like carbarasone is converted to trivalent inorganic compound , by digestion with sulphuric acid and potassium sulphate. Only small amount of bromine discharge the color of methyl orange or methyl red added as an indicator at the end point. Sodium thiosulphate can be standardized by using potassium bromate as primary standard. E.g ( ref) same as Preparation & std of 0.1 m sodium thiosulphate

23. Application of redox titration: Redox titration is used in pharmaceutical analysis in the determination of % purity of pure drugs as well as its formulations. Various chemicals like caustic soda, chlorine etc are produced using redox titration. redox titration are useful in preventing corrosion as well as rusting of metals. The industrial production of cleaning products involves the oxidation process. The redox titration are used to determine the content of dissolved oxygen, in natural water sources like as rivers. This techniques also find its application in determination od salt in cheese and butter.

24. THANK Y OU