Pharmaceutical Analytical Chemistry Lecture 4 PDF

PC 215 Teams Code: 67q0715 Lecture 4 Dr. Christine Kamal Nessim  Outline: Redox titration √ - Redox principles & Electrical properties of redox systems √ - Nernst equation & Factors affecting oxidation potential √ - Detection of endpoint in redox titration -...

PC 215 Teams Code: 67q0715 Lecture 4 Dr. Christine Kamal Nessim  Outline: Redox titration √ - Redox principles & Electrical properties of redox systems √ - Nernst equation & Factors affecting oxidation potential √ - Detection of endpoint in redox titration -Standard Oxidants & Reductants - Applications of redox titration Potentiometry Conductometry Water Analysis 2  Learning Outcomes Understand the pharmaceutical and analytical terms, abbreviation, and symbols related to electrochemical analysis. Implement the knowledge of fundamental sciences to handle and analyze the synthetic pharmaceutical materials. Apply proper instrumental techniques for standardization of raw materials. Recognize the proper techniques for the analysis of pharmaceuticals and raw materials. 1) According to the following cell: ……………………..… ……………………..… Overall cell reaction ……………………..… The cell may be represented as ……………………..… 2) According to the equations, Choose from the following: Oxidant ……………………..…(Oxidant – Conjugate reductant) Reduced form ……………………..… (Oxidized form – Reduced form)  Fe3+ External Internal Starch The color of the oxidized form differs from the color of the reduced form. The color change of the indicator depends on its oxidation potential relative to the oxidation potential of the redox system. Example: the titration of sample reducing agent against standard oxidant:  Examples of internal redox indicators: or fluoride. It can be used only if we add phosphate or fluoride to complex ferric and lower oxidation potential of Fe3+/ Fe2+ system. It is used in titration of Fe2+ with Ce4+. It has high E It has only disadvantage is that it is expensive.  4- Potentiometric method (Redox Reactions( Indirect potentiometry (potentiometric titration): Types of potentiometric titration and titration curves (neutralization, complexometric, preciptimetric, and redox) Detection of end point: by measuring the change in the potential developed on the indicator electrode either by zero order (E versus mL of titrant) or first (∆E/ ∆V versus Vav mL) or second derivative (∆2E/ ∆V2 versus mL of titrant). V E ΔV ΔE ΔE Vav Δ (ΔE Δ Vav Δ (ΔE (mL) (mv) /ΔV /ΔV) /ΔV) / Δ Vav  Select true or false for each sentence 1- Orthophenanthroline is an example of a specific indicator in redox titration 2- Starch is a specific indicator for iodide 3- Oxidation potential of the redox indicator must be intermediate between both the oxidant and the reductant, and the difference must be at least 0.15 volt 4- Diphenylamine & SCN are an examples of internal redox indicators 5-Potassium permanganate is an example of a self indicator titrant  Examples of Redox Standards Standard Oxidants and Reductants I- Standard Oxidants:  1.45 Eq.wt = mol.wt / 1 However it is preferable to use Orthophenanthroline as indicator because the yellow color of cerric is not obvious especially in dilute solution. - Can be used for determination of ferrous.  Eq.wt = mol.wt / 6 - Can be used for determination of ferrous  Eq.wt = mol.wt / 2 -Although it has a lower oxidizing power than the previously mentioned oxidants, but it has wide applications. - It is brown in aqueous solutions and violet in organic solvents (chloroform). - Its specific indicator is starch. - It could be determined by titration against sodium thiosulphate. where you have a Where iodine is used as oxidizing substance agent in the burette, it will be the in the flask titrant. as a sample where it is determined by using sodium thiosulfate. Any titration involving Iodine, starch indicator is used which gives blue color with iodine, but if the medium is strongly acidic, starch can’t be used as it is hydrolyzed by the acidic medium, so we use chloroform. Iodine has violet color in chloroform layer.  II- Standard Reductants: 1- Sodium oxalate: - It is a primary standard reducing agent. - It is used for standardization of permanganate solution. 2- Sodium thiosulphate: Na2S2O3 - It is not a primary standard substance because of the uncertainty of the exact water content. - Solution of Na2S2O3 upon standing suffers decomposition with precipitation of sulphur (Na2S2O3 Na2SO3 + S°). (This reaction is accelerated by presence of CO2 and bacteria. Thus, we usually use recently boiled and cooled water, and small amounts of Borax and chloroform as disinfectant could be added to the standard solution). - For a complete quantitative redox reaction to proceed, the oxidation potential difference between oxidizing agent and reducing agent must be at least 0.4 V. If the difference is less than 0.4 V the reaction will proceed but will not be a complete quantitative reaction. - Oxidation potential of the redox indicator must be intermediate between both the oxidant and the reductant, and the difference must be at least 0.15 volt. Applications of Redox titration Determination of Ferrous sulphate: (E = +0.77 v) a- By titration # std. KMnO4 in dil H2SO4 Determined by titration against KMnO4 (pink) which act as a self indicator, the medium should be acidic. Ferrous is oxidized to ferric where permanganate is reduced to Mn2+ (colorless) so the endpoint will be the first appearance of pink color. b- By titration # std. K2Cr2O7 Determined by titration against dichromate as a titrant and diphenylamine (E = 0.76 V) as an indicator, but phosphoric acid must be added. If we used Orthophenanthroline (E = 1.06 V) or Phenylanthranilic acid as an indicator, there is no need to add phosphoric acid. c- By titration # std. Ceric sulphate Determined by titration against cerric sulphate as a titrant and Orthophenanthroline as indicator, there is no need to add phosphoric acid. Determination of Ferrous chloride:  3 es- + MnO4 1- + 4 H+ ………. + 2 H2O a) MnO42- b) MnO2 c) Mn2+ d) None of them A ……………………. is an indicator which undergoes a definite color change at a specific potential a) Redox indicator b) Self indicator c) Starch indicator d) Both A &B Iodimetry titrations: a) A reducing analyte b) One reaction c) Standard solution: Iodine d) All of the above Solubility of iodine in water may be increased by adding a) Chloroform b) Potassium iodide c) Carbon disulphide d) Sodium thiosulphate  1- The potential which is developed on Zinc electrode when immersed in zinc sulphate is called: a) Oxidation potential b) Standard oxidation potential c) Standard electrode potential d) Electrode potential 2- I2 can oxidize AsO33– by rendering the medium alkaline by……….. a) Phosphate b) F- c) Mn2+ d) NaHCO3 3- Zimmermann's reagent composed of all of the following except …… a) Sulphuric acid b) Iodine c) Manganese sulfate d) Phosphoric acid 4- In galvanic cell composed of Zinc and Cupper electrodes, zinc electrode serves as: a) The cathode b) Salt bridge c) The anode d) Ionic pressure 5- Platinum electrode may acquire -ve charge when the redox system is oxidizing because it gains electrons from Platinum a) True b) False 6- Addition of Zn2+ to Ferricyanide/Ferrocyanide system cause the oxidation potential to a) Decrease b) Not changed c) Increase d) None of the above