CJC_H2_CHEM_P3 Prelim

CATHOLIC JUNIOR COLLEGE JC2 PRELIMINARY EXAMINATIONS Higher 2 CANDIDATE NAME CLASS 2T CHEMISTRY 9647/03 Paper 3 Free Response THURSDAY 25 AUGUST 2011 2 Hours Candidates answer on separate paper. Additional Materials: Answer Paper Data Booklet READ THESE INSTRUCTIONS FIRST Write your name and class on all the work you hand in. Write in dark blue or black pen on both sides of the paper. [PILOT FRIXION ERASABLE PENS ARE NOT ALLOWED] You may use a soft pencil for any diagrams, graphs or rough working. Do not use staples, paper clips, highlighters, glue or correction fluid. Answer any four questions. A Data Booklet is provided You are reminded of the need for good English and clear presentation in your answers. The number of marks is given in brackets [ ] at the end of each question or part of the question. At the end of the examination, fasten all work securely together. This document consists of 11 printed pages and 1 blank page. [Turn over] For Examiner’s Use Paper 3 Q 1 20 Q 2 20 Q 3 20 Q 4 20 Q 5 20 Total 80

2 9647/03/CJC JC2 Prelim Exam 2011 BLANK PAGE

3 9647/03/CJC JC2 Prelim Exam 2011 Answer any four questions. 1 Nanochemistry is an important field of science that explores the use of extremely small particles that have diameters about thousand time s thinner than the width of a human hair. Transition metals and its compounds are often the subject of interest in nanochemistry, as many useful properties are improved at this ultra small scale. (a) Nano-sized iron( III) hydroxide, Fe(OH) 3 exists as a precipitate and can be used as a catalyst to remove aqueous arsenate( V) ions, AsO 4 3- from contaminated water. The Fe(OH)3 with the adsorbed arsenate( V) ions are filtered off, and undergoes an ion- exchange with the arsenate( V) ions removed and Fe(OH) 3 precipitate recovered unchanged. (i) State the electronic configuration of iron in Fe(OH) 3. (ii) State the type of catalysis and briefly explain why transition metal compounds are suitable for such catalysis. (iii) Suggest why the use of nano-sized particles will improve this catalytic property. [4] (b) Nano-sized iron(II) hydroxide exists as a complex solid with the formula Fe(H 2O)4(OH)2 and has no net dipole moment. (i) State the colour and coordination number of the complex iron( II) hydroxide. (ii) Suggest the structure of the complex solid, given that it is a non-polar species. [4] (c) Nano-sized iron(II) hydroxide, Fe(OH)2 is often unstable, due to oxidation by water even though oxygen is not present. The pH of the solution remains largely unchanged, a reddish-brown precipitate and effervescence are observed. (i) Identify the reddish-brown precipitate and suggest an equation for this reaction. (ii) The reaction is not expected to occur under standard conditions and can be considered reversible. Suggest a