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Reg. No:……………………………. KIGALI INSTITUTE OF SCIENCE AND TECHNOLOGY INSTITUT DES SCIENCES ET TECHNOLOGIE Avenue de l'Armée, B.P. 3900 Kigali, Rwanda INSTITUTE EXAMINATIONS – ACADEMIC YEAR 2012/2013 END OF SEMESTER II SUPPLEMENTARY EXAMINATION FACULTY OF SCIENCE SCIENCE 4-CHEMISTRY SECOND YEAR, EXAM SEM. II CHE 3221-ANALYTICAL CHEMISTRY II DATE: 28/06/2013 TIME: 2 HOURS MAXIMUM MARKS = 60 INSTRUCTIONS 1. This paper contains TWO sections 2. Answer Question ONE in section A, and any TWO out of the THREE Questions in section B 3. No written materials allowed. 4. Write all answers in the booklet provided. 5. Do not forget to write your Registration Number. 6. Do not write any answers on this question paper Section A 1. a. If the absolute uncertainty in reading a buret is constant at ±0.02 mL, what will be the percent relative uncertainty: (a) for a volume of 15 mL, (b) for a volume of 0.085 L. (4 marks) b. With a schematic diagram, explain how Gravimetric combustion analysis for carbon and hydrogen is achieved (6 marks) c. How might the number of theoretical plates in a chromatographic column be determined? (2 marks) d. State classification of analytical methods by filling the following table with required information: (4 marks) Name of the method Basic principle Electroanalytical methods Determination of the mass of the analyte or some compound related to it. Titrimetric methods based on measurement of the interaction between electromagnetic radiation and analyte e. Calculate the concentration of Pb2+ in a solution that was prepared by mixing 22.0 ml of 0.0300 M Pb2+ and 15.0 ml of 0.0440 M EDTA. The mixture was buffered at pH of 7.75 (look for constants at the end of this questionnaire) (4 marks) Section B 2. a. State four desirable properties of a gravimetric precipitate (2 marks) b. Why is high relative supersaturation undesirable in a gravimetric precipitation? (2 marks) c. Consider the following arithmetic calculation and determine the absolute uncertainty accompanying the answer: (3 marks) d. Describe systematic error citing a relevant example (2 marks) e. Explain why in iodometry method of analysis iodine is normally used in a solution containing excess I–? Show the reaction occurring in that solution (2 marks) f. Citing a specific example explain the precipitation from homogeneous solution (3 marks) g. To find the Ce4+ content of a solid, 4.37 g were dissolved and treated with excess iodate to precipitate Ce(IO3)4. The precipitate was collected, washed well, dried, and ignited to produce 0.104 g of CeO2 (FM 172.114). What was the weight percent of Ce (FM 140.1) in the original solid? (6 marks) 3. a. In Potentiometric Titration, iron(II) ions (Fe2+) concentration is determined by permanganometry explain briefly this technique giving the balanced reaction involved (4 marks) b. With the Aid of a sketch, explain the Standard Hydrogen Electrode (S.H.E) c. 0.649-g sample containing K2SO4 (FM 174.27) and Al2(SO4)3 (3 marks) (FM 342.15) was dissolved in water and treated with Ba(NO3)2 to precipitate all sulfate as BaSO4 (FM 233.39). We want to know the percent weight of K2SO4 in the sample if 0.977 g of precipitate was formed. i. Write 2 equations necessary to solve this problem (3 marks) ii. Calculate % K2SO4in the sample (6 marks) d. Marie Curie dissolved 0.091 92 g of RaCl2 and treated it with excess AgNO3 to precipitate 0.088 90 g of AgCl. In her time (1900), the atomic mass of Ag was known to be 107.8 and that of Cl was 35.4. From these values, find the atomic mass of Ra that Marie Curie would have calculated. (4 marks) 4. a. Why Ethylene Diamine tetraacetic Acid (EDTA) is the most and widely utilized chelating agent (3 marks) b. One of the indicators for titrations using EDTA is Eriochrome Black T. Give its chemical formula and show its color before and after equivalence (2 marks) c. During a titration of 30.0 ml of a palladium (II) solution, 15 mL of 0.020M EDTA is used to reach the end –point in a solution buffered to constant pH= 11 (α4 = 0.846) i. Determine 3 preequivalence-point values for pPd (at 0 mL ; 6 mL and 12 mL of EDTA added) (3 marks) ii. Calculate the pPd at equivalence- point (3 marks) iii. Determine 3 postequivalence-point values for pPd (at 16 mL; 18mL and 22mL of iv. EDTA added) (6 marks) Derive the curve of this titration (3 marks) EDTA constants: K1, K2, K3, K4 are respectively 1.02 x 10-2, 2.14 x 10-3, 6.92 x 10-7, 5.50 x 10-11