RI_H2_CHEM_P3 Prelim

© Raffles Institution 2016 9647/03/S/16 [Turn Over 1 RAFFLES INSTITUTION 2016 YEAR 6 PRELIMINARY EXAMINATION Higher 2 CHEMISTRY 9647/03 Paper 3 Free Response 16 September 2016 2 hours Candidates answer on separate paper. Additional Materials: Answer Paper Data Booklet READ THESE INSTRUCTIONS FIRST Do not open this question booklet until you are told to do so. Write your name, class and index number on all the work you hand in. Write in dark blue or black pen on both sides of the paper. 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. Begin each question on a fresh sheet of paper. A Data Booklet is provided. Do not write anything in it. You are reminded of the need for good English and clear presentation in your answers. 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. This document consists of 12 printed pages.

© Raffles Institution 2016 9647/03/S/16 [Turn Over 2 Answer any four questions. Begin each question on a fresh sheet of paper. 1 (a) Gallium trichloride, GaC l3, can be formed by direct combination of the elements. It has a melting point of 78 C. Suggest the type of chemical bonding present in GaC l3 and explain why gallium has a high tendency to form chlorides of this nature. [2] (b) Gallium hydride, with empirical formula GaH3, can be prepared from GaCl3. A 0.55 g sample of gaseous gallium hydride occupies a volume of 68 cm 3 at a temperature of 243 K and a pressure of 1.12 x 105 Pa. Determine the Mr of gallium hydride and hence its molecular formula. [3] (c) GaH3 reacts with (CH 3)3N at 178 K to give compound A, which has the following composition by mass: H, 11.0%; C, 37.8%; N, 14.7%; Ga, 36.5%. A molecule of compound A has only one Ga atom. (i) Determine the molecular formula of A. [1] (ii) Draw a structure to show clearly  the shape of A around the gallium atom and  the types of bonds around the gallium atom. [2] (d) Lithium aluminium hydride, LiA lH4, and lithium gallium hydride , LiGaH4, are both donors of hydride, H−. Thus, they are capable of reducing a large number of organic molecules. Suggest a possible reason why LiAlH4 is a stronger reducing agent than LiGaH4. [1] (e) LiAlH4 can be used to reduce amides to amines as shown below: 2 1 1 2 DEET is the active ingredient in many insect repellents. The following reaction scheme involves the preparation and reaction of DEET. LiAlH4 in dry ether B DEET step 3 LiAlH4 in dry ether step 1 step 2

© Raffles Institution 2016 9647/03/S/16 [Turn Over 3 (i) Suggest the structures of compound B and DEET. [2] (ii) Suggest the organic reactant used in step 2