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 your equation. [1] (ii) Only one of the students successfully prepares 2-hydroxybutanoic acid. Identify which compound, G or H, is 2-hydroxybutanoic acid and explain the difference between reactions 2 and 3. …………………………………………………………………………………………. …………………………………………………………………………………………. …………………………………………………………………………………………. [2] (c) Draw a labelled diagram to show how hydrogen bonding occurs between two molecules of butane-1,2-diol. [2]

4 ¤ Jurong Pioneer Junior College 9729/02/J2 PRELIMINARY EXAM/2021 (d) Like butane-1,2-diol, compound J contains only carbon, hydrogen and oxygen. The following information of J is known. x J has a Mr of 192 and does not rotate plane polarised light. x Complete combustion of 4.32 g of compound J produces 5.94 g of CO2 and 1.62 g of H2O. x 1 mole of J requires 3 moles of dilute NaOH for complete neutralisation. Calculate the C:H ratio and deduce the molecular formula of J. Hence, suggest a possible structure for J. For ([DPLQHU¶V Use [3] [Total: 14]

5 ¤ Jurong Pioneer Junior College 9729/02/J2 PRELIMINARY EXAM/2021 [Turn Over BLANK PAGE

6 ¤ Jurong Pioneer Junior College 9729/02/J2 PRELIMINARY EXAM/2021 2 (a) Concentrated sulfuric acid is a versatile reagent. For ([DPLQHU¶V Use (i) When solid NaCl reacts with concentrated sulfuric acid, white fumes of HCl(g) and sodium hydrogen sulfate, NaHSO4, are formed. However, when solid NaI reacts with concentrated sulfuric acid, purple fumes of I2(g) and hydrogen sulfide gas, H2S(g), are also formed. State the role of concentrated sulfuric acid in each reaction. Explain how you arrive at your answer. x reaction of solid NaCl with conc. H2SO4 role of conc. H2SO4 ………………………………………. explanation ………………………………………………………………………... ………………………………………………………………………………………. x reaction of solid NaI with conc. H2SO4 role of conc. H2SO4 ………………………………………. explanation ………………………………………………………………………... ………………………………………………………………………………………. [3] (ii) Suggest why NaCl and NaI differ in their reactions with concentrated sulfuric acid. …………………………………………………………………………………………. …………………………………………………………………………………………. [1] (iii) The addition of concentrated sulfuric acid to solid sodium bromide, NaBr, produces reddish brown fumes and an acidic gas that decolourises acidified potassium manganate(VII) solution. This acidic gas is a significant contributor to acid rain. Complete the equation to show the reaction of concentrated sulfuric acid with sodium bromide. …. NaBr(s) + …. H2SO4(l) o …. NaHSO4(s) + …............ + ................. + …. H2O(l) [2]

7 ¤ Jurong Pioneer Junior College 9729/02/J2 PRELIMINARY EXAM/2021 [Turn Over (b) Butenone is shown. For ([DPLQHU¶V Use (i) By reference to the bonding, suggest why the H2C=C‒C=O part of the molecule is planar. …………………………………………………………………………………………. …………………………………………………………………………………………. [1] (ii) When mixed with concentrated sulfuric acid, butenone undergoes electrophilic addition reaction to give isomer P rather than isomer Q. Complete Fig. 2.1 to suggest a mechanism for this reaction. Include any dipoles, lone pairs and curly arrows to the movement of electron pairs. [2] (iii) With reference to the mechanism you have drawn in (b)(ii), explain why isomer Q is not produced. ………………………………………………………………………………………. …………………………………………………………………………………………. …………………………………………………………………………………………. [1]

8 ¤ Jurong Pioneer Junior College 9729/02/J2 PRELIMINARY EXAM/2021 (c) When isomer P is boiled in water, alcohol R is obtained, which undergo further reactions as shown below. For ([DPLQHU¶V Use (i) Name the types of reaction that occur during each of the steps 1 and 2. step 1 ……………………………………………………………………………. step 2 ……………………………………………………………………………. [2] (ii) Draw the structures of T, U and V. T U V [3] (iii) In step 3, Ni was used as a heterogeneous catalyst. Explain how this type of catalysis works. ………………………………………………………………………………………… ………………………………………………………………………………………… ………………………………………………………………………………………… ………………………………………………………………………………………… ………………………………………………………………………………………… ………………………………………………………………………………………… [2]

9 ¤ Jurong Pioneer Junior College 9729/02/J2 PRELIMINARY EXAM/2021 [Turn Over (iv) S exists as a mixture of two stereoisomers. Draw the structure of each stereoisomer of S and explain how this type of isomerism arise. For ([DPLQHU¶V Use ………………………………………………………………………………………… ………………………………………………………………………………………… ………………………………………………………………………………………… [3] [Total: 20]

10 ¤ Jurong Pioneer Junior College 9729/02/J2 PRELIMINARY EXAM/2021 3 Benzenediazonium chloride, C6H5N2Cl, is readily hydrolysed at temperatures above 5 qC. C6H5N2Cl(aq) + H2O(l) o C6H5OH(aq) + N2(g) + HCl(aq) Some chemists investigate the rate of this hydrolys