Redox titration.pptx

Redox titration

1. UNIT IV REDOX TITRATION BY Mrs. Shinde Pooja Nilkanth SPM`S College Of Pharmacy, Akluj

2. Introduction Concept of oxidation and reduction Oxidation – Oxidation reaction is defined as loss of electron. Reduction - Reduction is defind as gain of electron. Oxidation reduction reaction Oxidation reduction reaction is chemical process in which oxidation reduction occurs simultaneously which leads to change in valency of reacting element. If one atom undergoes an oxidation process second atom undergoes to reduction.

3. ghghg Oxidising agent - Oxidising agents is defind as substances which containing an atom or ion which gains an electron and result in either decrease in positive valency or increase in negative valency. It includes halogens and certain compounds containing metal or non metal in the state of higher valency. Example – KMno 4, K 4 Cr 2 O 7

4. ab Reducing agent – Reducing agents is defind as substance which containing atom or ion that looses electron and result in either increase in positive valency and decrease in negative valency. It includes metal and compounds containing metal or non metal in state of lower valency. Example – FeCl 2 , H 2 S.

5. ab Redox potential – Oxidising agent accepts electron and get reduced. Reducing agent donates electron and get oxidised. Due to transfer of electrons, changes in valency of atoms or ions takes place which leads to positive valency of oxidized atom or ions increases and reduced atom or ion decreases. Strong oxidising agent having capacity to accept electron from many weak reducing agents.

6. ab Weak oxidising agent have less capacity to accept electron hence they can oxidise only strong reducing agents The way of redox reaction can be forecast by characteristics of reactant, this characteristic is called as Redox potential. Redox potential is measured by measuring potential difference between two systems by connecting both to galvanic cell. System consist of oxidising and reduced form of chemical element.

7. Equivalent weights of oxidizing and reducing agents Equivalent weight of oxidizing and reducing agents are calculated by number of electron accepts or donates by an atom or ion during redox reaction. Examples Oxidising agents Potassium permanganate (KMnO 4 ) Permanganate ion in acidic medium form manganous ion MnO 4 + 8H +5e Mn ++ + 4H2O

8. ab Equivalent weight of KMnO4 = Molecular weight 5 In neutral medium the product is manganese dioxide. MnO-4 + 4H +3e MnO2 + 2H2O Equivalent weight of KMnO4 = Molecular weight 3

9. Detection of end point Internal indicator These indicators shows different colour in oxidized and reduced form. Internal indicators shows sudden change in redox potential near to end point. Example Ferroin – It has red colour in reduced form and pale blue colour in oxidized form. 1% solution of diphenylamine in conc. sulphuric acid – colourless in reduced form and violet colour in oxidized form.

10. ab Self indicators Some reagents shows change in colour due to redox reaction and may serve as their own indicator are called as self indicator and such reactions do not need any indicator for detection of end point. Example Potassium permanganate - shows pink colour Iodine - shows brown colour But this type of indicators has the disadvantage that an excess of oxidizing agent is always present at the end point, to reduce error blank determination is required.

11. ab External indicator In this type of indicator few drops of titration solution separated periodically from flask and mixed with indicator which shows colour change at the equivalence point. Example Ferrous ions gives deep blue colour in presence of potassium ferricyanide .

12. ab Instrumental method This method is employed when visual indicator method fails or has limited accuracy. End point determined by use of potentiometer or conductometer.

13. Types of redox titrations Redox titration Permagnometry Cerimetry Iodimetry Iodometry Dichrometry Bromatometry

14. PERMAGNOMETRY In this method potassium permanganate (KMnO 4 ) is used as oxidizing agent and as self indicator. Potassium permanganate is secondary standard can also be standardized by using primary standard like oxalic acid and arsenic trioxide. Limitation – It is difficult to get potassium permanganate in pure form and completely free from manganese dioxide.

15. ab Applications – Used for assay of hydrogen peroxide, ferrous sulphate, ferrous ammonium sulphate. For determination of nitrates and perchlorates Determination of calcium as calcium oxalate. Etamesylats is haemostatic determined

16. Dichrometry Potassium dichromate is used as oxidising agent and it is weak oxidising power as compare to potassium permanganate. But has some advantage that is available in pure form, thermally stable, has definite shelf life and less expensive. Potassium dichromate rduced rapidly at ordinary temperature in acidic medium to form green chromium salt.

17. ab Applications Determination of iron in iron ore Determination of chromium in chromium salt Chemical oxygen demand can be determined by dichrometry .

18. Cerimetry Cerric ammonium sulphate is used as oxidising agent ad it is powerful oxidising agent. Cerric solution has bright yellow colour but on reduction cerous salt is colourless. Applications Used for assay ferrous fumarate. For determination of copper and molybdate. Following dosage forms are detrmined by using Cerimetry.

19. ab Ferrous gluconate (tablets) Ferrous fumarate (tablets) Ferrous succinate (tablets) Ferrous sulphate dried Ferrous sulphate (tablets) Paracetamol Ascorbic acid (tablets)

20. Iodimetry Determination of iodine is done in Iodimetry. Iodine is weak oxidant and easily reduced by stannous chloride, sodium thiosulphate and arsenic oxide. Known volume of standard iodine solution is titrated directly with reluctant by using starch as indicator. Applications 1 . For determination of reductant like stannous chloride, sulphurous acid, sodium thiosulphate, and arsenic oxide.

21. ab 2. Determination of analgine and acetarsol. 3. Assay of ascorbic acid, sodium ascorbate and sodium thiosulphate.

22. Iodometry In Iodometry iodine is liberated in analyte solution through oxidation of iodine and liberated iodine is titrated with strong reductant . Applications Determination of KMnO 4, copper sulphate, hydrogen peroxide, potassium dichromate. Determination of chlorine in hypochlorite. Determination of thyroxine in thyroid gland. Detrmination of ferric ammonium citrate.

23. Bromatometry Potassium bromate is used as oxidising agent, mainly used for determination of inorganic reducers. Bromatometry done by two methods Direct Indirect Direct method - titration is carried out in presence of HCl with bromate solution. Indirect method – Excess bromine is added then excess of bromine is determined iodometrically

24. ab That is by adding excess of KI and liberated iodine is determined by sodium thiosulphate solution. Applications Various metals like aluminium, iron copper, zinc, cadmium, cobalt. Nickel determined by using hydroxyquinoline and bromatometry. Determination of phenols. Determination of Hydroxylamine