Download Exam Document for Chemistry and Biopharmaceutical Chemistry - Semester 1, 2011 and more Exams Physical Chemistry in PDF only on Docsity! Semester 1 Examinations 2011 Exam Code(s) 4BS; 4BPC Exam(s) 4th year Chemistry and 4th year Biopharmaceutical Chemistry Module Code(s) CH429 Module(s) PHYSICAL CHEMISTRY Paper No. 1 Repeat Paper External Examiner(s) Prof. Paul Seakins Internal Examiner(s) Prof. P. Murphy Dr. W. M. Carroll, Dr. H. Curran, Dr. D. Leech, Dr. A. Ryder Instructions: ANSWER THREE (3) QUESTIONS ONE FROM EACH SECTION Duration Two (2) Hours No. of Pages 5 Department(s) Chemistry Course Co-ordinator(s) Dr. W. M. Carroll Requirements: MCQ Release to Library: Yes No Statistical/ Log Tables x Graph Paper x Gas constant, R = 8.3143 J K–1 mol–1 Avogadro constant, NA = 6.022 × 10 23 mol–1 Planck constant, h = 6.624 × 10–34 J s Velocity of light, c = 2.998 × 108 m s–1 Electronic charge, e = 1.602 × 10–19 C Boltzmann constant, kB = 1.381 × 10 –23 J K–1 Electronic mass, m = 9.109 × 10–31 kg Bohr magneton, B = 9.274 × 10–24 J T–1 Faraday constant, F = 96,485 C mol–1 1 atmosphere = 101,325 N m–2 SECTION A 1. Answer all parts. (a) Describe the differences between static and dynamic quenching of fluorescence. With the aid of diagrams how static and dynamic quenching can be discriminated by measurement of fluorescence parameters. [30 marks] (b) Describe with the aid of diagrams how the effect of combined static and dynamic quenching might be discriminated using fluorescence measurements.[10 marks] (c) Show with the use of the relevant equations how one would modify the Stern- Volmer equation to accommodate the two effects, and generate a straight line plot. [30 marks] (d) The following normalized fluorescence data were obtained for quenching of fluorescence from an aqueous solution of an amino acid by KI water at near ambient temperatures. Construct a Stern-Volmer plot, and calculate the Stern- Volmer constant. Calculate the observed bimolecular quenching constant. The unquenched lifetime τ0 =4.3 ns. KI [M] 0.0 0.04 0.10 0.20 0.30 0.50 0.80 I0/IF 1.0 4.64 10.59 23.00 37.20 68.60 137.00 [30 marks] 2. In a flow study of the reaction between fluorine atoms and chlorine at 300 K, the concentration of Cl2 was measured with a mass spectrometer being proportional to the signal S obtained at various distances d downstream from the point of mixing. The flow velocity was 53 ms–1, at a total pressure of 150 Pa, and at an initial F•concentration of 1.70 × 1012 atoms cm–3 (much greater than that of Cl2) . F• + Cl2 →ClF + Cl• S 72.0 50.5 35.6 24.2 d / mm 65 135 200 275 Draw a schematic diagram of a flow tube apparatus that you would use to measure the F• + Cl2 reaction under conditions where F• >> Cl2 and Cl2 is detected by mass spectrometry. Show in your figure how F• atoms are generated. [25 marks] From the data provided above, find the rate constant for the reaction [25 marks] Compare your results with collision frequency. Collision radii of 135 and 165 pm may be assumed for F• and Cl2, respectively. [40 marks] Based on your comparison, is there a significant activation energy for this reaction? [10 marks]
