HCI 2018_H2_CHEM_P3_QP Prelim

This document consists of 11 printed pages. HWA CHONG INSTITUTION C2 Preliminary Examinations Higher 2 CANDIDATE NAME CT GROUP 17S CENTRE NUMBER INDEX NUMBER CHEMISTRY Paper 3 Free Response Candidates answer on separate paper. Additional Materials: Answer Paper Data Booklet 9729/03 18 September 2018 2 hours READ THESE INSTRUCTIONS FIRST Write your name, CT group, centre number and index number clearly in the spaces above. Write in dark blue or black pen. You may use a HB pencil for any diagrams or graphs. Do not use staples, paper clips, glue or correction fluid. Section A Answer all questions. Section B Answer one question. Begin each question on a new sheet of writing paper. A Data Booklet is provided. The use of an approved scientific calculator is expected, where appropriate. At the end of the examination, fasten all your work securely together. The number of marks is given in brackets [ ] at the end of each question or part question. Circle the question number for the question that you have attempted for Section B on the cover page provided.

2 © Hwa Chong Institution 2018 9729 / 03 / C2 Prelim 2018 Section A Answer all the questions in this section. 1 (a) Aluminium is a major component used in the manufacture of various parts of airplanes. With the aid of a labelled diagram, describe the structure and bonding in aluminium. [3] (b) Pure aluminium is too soft to be used directly for aircraft applications. An alloy of aluminium is used instead to improve its tensile strength and corrosion resistance. One such alloy is aluminium bronze, which contains aluminium, copper and iron. To determine the percentage by mass of copper in the alloy, an experiment is performed with the following procedure: step 1: Concentrated HNO 3 is added to a 1.20 g sample of the alloy. The mixture is then heated until all the solid dissolves. The resulting solution, which contains Cu 2+, Fe2+ and Al3+ ions, is cooled and diluted. step 2: H 2O2(aq) is added dropwise until no further change is observed. step 3: Excess concentrated NH 3 is added to the solution. The resulting mixture is filtered and a dark blue solution is obtained as filtrate. step 4: HNO 3(aq) is added to the filtrate until no more traces of precipitate is observed in the solution. step 5: Excess K I(aq) is added to the resulting solution. The reaction produces brown iodine and a white precipitate of copper(I) iodide, CuI. 2Cu2+(aq) + 4I−(aq) → I2(aq) + 2CuI(s) A filtration is performed again, and the filtrate is made up to 250 cm 3 in a volumetric flask. step 6: 25.0 cm 3 of this solution is titrated with aqueous sodium thiosulfate, Na2S2O3(aq), in the presence of starch indicator. I2(aq) + 2S2O32−(aq) → 2I−(aq) + S4O62−(aq) (i)