JPJC 2021 H2 Chemistry P2 QP Prelim

¤ Jurong Pioneer Junior College [Turn Over NAME CLASS 20S JURONG PIONEER JUNIOR COLLEGE JC2 PRELIMINARY EXAMINATION 2021 CHEMISTRY 9729/02 Higher 2 Paper 2 Structured Questions 15 September 2021 2 hours Candidates answer on the Question Paper. Additional Materials: 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. You may use a HB pencil for any diagrams or graphs. Do not use staples, paper clips, glue or correction fluid. Answer all questions in the spaces provided on the Question Paper. The use of an approved scientific calculator is expected, where appropriate. A Data Booklet is provided. The number of marks is given in brackets [ ] at the end of each question or part question. For Examiner’s Use 1 14 2 20 3 11 4 15 5 15 Penalty (delete accordingly) Bond linkages –1 / NA Significant figures & units –1 / NA Total 75 This document consists of 17 printed pages and 1 blank page.

2 ¤ Jurong Pioneer Junior College 9729/02/J2 PRELIMINARY EXAM/2021 Answer all the questions. 1 (a) The reducing agent LiAlH4 can be synthesised by reacting aluminium chloride with lithium hydride, LiH. For ([DPLQHU¶V Use (i) Lithium hydride contains the ions Li+ and H–. State the electronic configuration of these two ions. Li+ ………………………………………… H– ……………………………………. [1] (ii) Explain why Li+ ion has a smaller radius than H– ion. …………………………………………………………………………………………. …………………………………………………………………………………………. [1] (iii) LiAlH4 decomposes slowly according to the mechanism below. Step 1 3LiAlH4 o Li3AlH6 + 2Al + 3H2 Step 2 2Li3AlH6 o 6LiH + 2Al + 3H2 Step 3 2LiH + 2Al o 2LiAl + H2 Use the above mechanism to deduce the overall equation for this decomposition. …………………………………………………………………………………………. [1] (iv) LiAl(s) has a melting point of 718 qC and conduct electricity when in solid and molten states. Suggest the structure and describe the type of bonding for LiAl(s). …………………………………………………………………………………………. …………………………………………………………………………………………. …………………………………………………………………………………………. …………………………………………………………………………………………. [2] (v) Assuming the same packing arrangement of atoms, suggest why LiAl(s) has a lower density than Al(s). …………………………………………………………………………………………. …………………………………………………………………………………………. [1]

3 ¤ Jurong Pioneer Junior College 9729/02/J2 PRELIMINARY EXAM/2021 [Turn Over (b) Two students try to prepare 2-hydroxybutanoic acid in the laboratory. Both students oxidise butane-1,2-diol to form F in reaction 1. One student then reduces F using LiAlH4. G is formed. The other student reduces F using NaBH4. H is formed. For ([DPLQHU¶V Use (i) Complete the equation to show the conversion of butane-1,2-diol to F in reaction 1. Use [O] to balance you