SOHAG UNIVERSITY FACULTY OF PHARMACY PHARM. ANAL. CHEM. DEPT. Pharm. Anal. Chem-2 Second Year Students May, 31, 2016 TIME ALLOWED: TWO HOURS Total marks: 90 All Questions are to be attempted 1- Redox Titration (35 Marks) Question 1: A- Write the balanced equation of the reaction between potassium permanganate and ferrous sulfate in acid medium. (2 Marks) B- Calculate the equilibrium constant (K eq ) of the above reaction (E 0 Fe +3 /Fe +2 = 0.77 V, E 0 MnO4- /Mn +2 = 1.52 V) (2 Marks) B- If chloride ions present in the above solution, what is the Problem? Mention How it can be overcome? (2 Marks) 1
Question 2: Mark ( ) for the correct statement and ( X ) for the wrong one and correct the wrong (Each item one Mark) 1- Starch is the specific indicator in all titrations involving iodine. ( ) 2- M 0 /M n+ system of positive potential can oxidize and displace those of negative potential. ( ) 3- Titrations with ceric sulfate can be applied in alkaline medium. ( ) 4- The sign of the standard electrode potential is similar to charge on the electrode. ( ) 5- Diphenylamine is a redox indicator (E 0 =0.76, n=2), accordingly, its E 0 range from 0.75 0.78. ( ) 6- The lower the ph, the weaker the oxidation potential of AsO 3-3- 4 /AsO 3 system. ( ) 7- H 2 O 2 behaves as oxidant and reductant. ( ) 8- Standard bromine solution can be prepared by dissolving bromine in water. ( ) 9- K 2 Cr 2 O 7 has more than equivalent weight at different ph. ( ) 10- Equivalent weight of Na 2 S 2 O 3 equals its half molecular weight. ( ) 11- When titrating 100 ml 0.1 N ferrous solution (E 0 Fe +3 /Fe +2 = 0.77 V) 2
with 100 ml 0.1N ceric solution (E 0 Ce 4+ /Ce 3+ = 1.44 V) in dil. H 2 SO 4, the potential at equivalence point equals 1.33 V. ( ) 2-12- Iodimetric determination of SO 3 is possible under anhydrous condition. ( ) 13- KMnO 4 can oxidize Cl -, Br - and I - at ph 5. ( ) 14- Metallic iron can displace Cu 2+ in its salts. ( ) 15- Methyl red is used as redox indicator when titrating AsO 3 3- BrO 3 - in acid medium. ( ) with 16- The oxidation product of thiosulfate, by reaction with oxidants stronger than iodine, is tetrathionate. ( ) 17- In weakly alkaline medium glycerol is oxidized by KMnO 4 into oxalate and CO 2. ( ) 18- Chloroform is the specific indicator in Andrew's method. ( ) 19- Isonicotinic acid hydrazide can be determined bromometrically and its reaction product is the bromoderivative. ( ) 20- In determination of copper salts by treatment with excess of KI thiocyanate must be added at the beginning of titration to prevent adsorption of I 2 on Cu 2 I 2. ( ) 3
Question 3: Explain, by equations only, How you can analyze the following: a) Iodine solution. (3 Marks) b) Mixture of acetic and formic acids. (4 Marks) c) Vitamin C (ascorbic acid). (2 Marks) 4
II-Compleximetry (20 marks) 1-Mention in one word or two words the scientific name or expression for the following : (7x1 points) a-a compound whose color changes when it binds to metal ion. ( ) b-chelating agent, non toxic, serves as an effective antidote for the treatment of lead poisoning. ( ) c-complex species containing two metal ions or more than two metal ions. ( ) d-the value which give the ratio of the total uncombined EDTA (in all forms ) to the fully ionized form. e-a substance added in complexation titration that prevents the formation of insoluble metal hydroxide but does not prevent the reaction of metal with EDTA. ( ) f-a type of EDTA titration in which the librated hydrogen ions are neutralized with standard alkali. ( ) g-substance refers to the release of a metal ions from a complex. ( ) 2-Explain (only be equations) how can you analyze the following: (2x2points) a-determination of iodide by mercuric chloride. b- Determination of copper by cyanometric method. 5
3-Write the most suitable indicator for each of the following titrations: a-lead ions with EDTA at ph 10 b-calcium ions with EDTA at ph 12. c-bismuth ions with thiosulphate at ph 1-3. d-mercuric ions with thiocyanate. e-halide ions with mercuric nitrate. f-zinc ion with EDTA at ph 10. (6x0.5 points) 4-Mark the following with right ( ) or wrong ( x) and correct the wrong one. (6x1 points) a-magnesium ions form stable complex with cyanide ions. ( ) b-aluminium ions block Erio T indicator. ( ) c-silver ions can be analyzed by direct titration with EDTA. ( ) d-the stability of EDTA complexes is affected only by ph. ( ) e-direct titration of calcium ions with EDTA, Eriochrome Black T gives a poor end point. ( ) f-ca-chelate is too weak to be titrated in acid solution, while mercury-chelate is strong enough to be titrated in that medium. ( ) 6
III. STATISTICS (15 marks) Ques. I (6 marks) In a titrimetric method, the following volumes were obtained: 10.0, 9.9, 9.0, 9.9 & 9.7 ml. -Should we reject or retain the outlier? -Calculate the standard deviation, the coefficient of variation, and the standard error of the mean for the five measurements. Rejection quotient, Q n 3 4 5 6 7 8 9 10 Confidence level Q 90 Q 95 Q 99 0.941 0.970 0.994 0.765 0.829 0.926 0.642 0.710 0.821 0.560 0.625 0.740 0.507 0.568 0.680 0.468 0.526 0.634 0.437 0.493 0.598 0.412 0.466 0.568 Ques. II Mention the validation parameters (performance criteria) for an analytical method. 1 6 2 7 3 8 4 9 5 10 (3 marks) 7
Ques. III (3 marks) Group A: Suggested methods for minimization of determinable errors: 1- Blank experiments. 2- Standard addition method. 3- Internal standard method. 4- Running a control determination. 5- Calibration of apparatus. 6- Use of independent method of analysis. Group B: Some examples of determinable errors: - Interference from excipients or additives of pharmaceutical formulations. - Errors due to variation in analytical techniques. - Impurities from some reagents or samples. - Errors due to experimental procedures or steps like boiling and cooling. - Errors due to equipments. - Variations in experimental chromatographic conditions (e.g. in HPLC). Put the proper number from group A into each of the items of group B. Ques. IV Differentiate by definitions between (a) & (b): (a) Accuracy: Precision: (3 marks) (b) Ruggedness: Robustness: Limit of detection: Limit of quantitation: WITH BEST WISHES 8