CJC_H2_CHEM_P3_ANSWER 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. ANSWERS This document consists of 11 printed pages and 1 blank page. [Turn over]

2 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. 1s22s22p63s23p63d5 or [Ar]3d5 (ii) State the type of catalysis and briefly explain why transition metal compounds are suitable for such catalysis. Fe(OH)3 act as a heterogenous catalyst. As transition metal compounds has empty d orbitals which can accept the lone pair of electrons from reactant species, and allow adsorption onto the transition metal compounds. (iii) Suggest why the use of nano-sized particles will improve this catalytic property. Nano-scaled particles have a larger surface area resulting in more\faster adsorption of the arsenate ions. [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. Green\Dirty Green\Grey Green. Coordination number is Six. (ii) Suggest the structure of the complex solid, given that it is a non-polar species. Fe OH2 OH OH2 OH2 HO OH2 II H2O H2O : : : : : : [4]

3 9647/03/CJC JC2 Prelim Exam 2011 (c) Nano-sized iron(II) hyd