Chemistry · 2018 · November · Paper 3 · SL · Question paper

28EP01 [Personal identifier removed] Standard level Paper 3 27 pages Thursday 8 November 2018 (morning) 1 hour Instructions to candidates yy Write your session number in the boxes above. yy Do not open this examination paper until instructed to do so. yy Answers must be written within the answer boxes provided. yy A calculator is required for this paper. yy A clean copy of the chemistry data booklet is required for this paper. yy The maximum mark for this examination paper is [35 marks]. Section A Questions Answer all questions. 1 Section B Questions Answer all of the questions from one of the options. Option A — Materials 2 – 4 Option B — Biochemistry 5 – 8 Option C — Energy 9 – 11 Option D — Medicinal chemistry 12 – 16 © International Baccalaureate Organization 2018 N18/4/CHEMI/ SP3/ENG/TZ0/XX 8818 – 6106 Section A Answer all questions. Answers must be written within the answer boxes provided. 1. Alloys containing at least 60 % copper reduce the presence of bacteria on their surface. The percentage of copper in brass, an alloy of copper and zinc, can be determined by UV-vis spectrometry. A sample of brass is dissolved in concentrated nitric acid and then made up to 250.0 cm3 with water before analysis. Cu (s) + 4HNO3 (aq) → Cu(NO3)2 (aq) + 2NO2 (g) + 2H2O (l) 3Zn (s) + 8HNO3 (aq) → 3Zn(NO3)2 (aq) + 2NO (g) + 4H2O (l) The concentration of copper(II) ions in the resulting solution is then determined from a calibration curve, which is plotted by measuring the light absorbance of standard solutions. Calibration curve 0 0 0.20 0.40 0.60 0.80 1.00 1.20 0.005 0.010 0.015 0.020 0.025 0.030 Concentration of Cu2+ ion / mol dm−3 Absorbance at chosen wavelength (This question continues on the following page) 28EP02 N18/4/CHEMI/ SP3/ENG/TZ0/XX – 2 –