2024 Prelims HCI H2 Chem P2 (QP)

This document consists of 18 printed pages and 2 blank pages. HWA CHONG INSTITUTION C2 Preliminary Examination Higher 2 CANDIDATE NAME CT GROUP 2 3 S CENTRE NUMBER S INDEX NUMBER CHEMISTRY Paper 2 Structured Questions 9729/02 28 August 2024 2 hours Candidates answer on the Question Paper. Additional Materials: Data Booklet READ THESE INSTRUCTIONS FIRST Write your name, CT group, centre number and index number 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. DO NOT WRITE ON ANY BARCODES. Answer all questions in the spaces provided in the Question Paper. The use of an approved scientific calculator is expected, where appropriate. A Data Booklet is provided. No. of sheets of writing paper submitted (if any) For Examiner’s Use 1 / 6 2 / 13 3 / 18 4 / 15 5 / 23 Deductions (s.f.) Deductions (units) Deductions (structures) Total / 75

2 © Hwa Chong Institution 2024 9729/02/C2 Preliminary Examination [Turn Over Answer all questions in the space provided. 1 (a) Complete the energy level diagram in Fig. 1.1, showing the relative energy levels of orbitals in the 3rd principal quantum shell. Fig. 1.1 [2] (b) (i) Explain what is meant by the term first ionisation energy. ……………………………………………………….……………………………………………… …………………………………………………………………………………………….……… [1] (ii) Use your knowledge of the variation in first ionisation energy of the Period 3 elements (Na to Ar) to predict and explain how the first ionisation energy varies in each pair of elements. • arsenic and selenium ……………………………………………………….……………………………………………… ……………………………………………………….……………………………………………… ……………………………………………………….……………………………………………… ……………………………………………………….……………………………………………… • bromine and krypton ……………………………………………………….……………………………………………… ……………………………………………………….……………………………………………… ……………………………………………………….……………………………………………… …………………………………………………………………………………………….………… [3] [Total: 6] energy

3 © Hwa Chong Institution 2024 9729/02/C2 Preliminary Examination [Turn Over 2 Polyfluoroalkyl substances (PFAS) is a group of compounds that have multiple fluorine atoms attached to an alkyl chain, giving these compounds waterproof properties, leading to widespread use in textiles, cosmetics, and food packaging. Poly(tetrafluoroethene), PTFE, is an early and popular example of PFAS made by polymerising tetrafluoroethene, F2C=CF2. (a) (i) State the shape and bond angle around the carbon atom in F2C=CF2. ……………………………………………………….……………………………………………... …………………………………………………………………………………………….…….. [2] (ii) Carbon atoms in F2C=CF2 are sp2 hybridised. Explain what is meant by sp2 hybridisation with reference to the carbon atom in F2C=CF2. ……………………………………………………….……………………………………………... ……………………………………………………….……………………………………………... …………………………………………………………………………………………….…….. [1] (iii) The shape of the carbon atom in F2C=CF2 depends on the arrangement of the hybridised orbitals. Apply the principles of the VSEPR theory to explain how the hybridised orbitals are arranged in the second shell of the sp2 carbon atom. ……………………………………………………….…………………………………………...… ………………………………………………………………………………………….……..…[1] (b) Explain why F2C=CF2 is a gas at room temperature whereas PTFE is a solid. ……………………………………………………….…………………………………………………..... ……………………………………………………….…………………………………………………..… ……………………………………………………….…………………………………………………..… ……………………………………………………….…………………………………………………..… …………………………………………………………………………………………………….….....[2] (c) In recent years, scientific evidence indicates that PFAS pose health and environmental concerns. Due to its persistence in the environment, it has been dubbed “forever chemicals”. Suggest why PFAS would last in the environment “forever”. ……………………………………………………….…………………………………………………..... ……………………………………………………….…………………………………………………..… …………………………………………………………………………………………………….….....[1]

4 © Hwa Chong Institution 2024 9729/02/C2 Preliminary Examination [Turn Over (d) The mechanism of polymerisation of PTFE consists of four separate stages A to D. A homolytic fission of an organic peroxide, RO–OR, produces two RO• radicals B RO• reacts with one F2C=CF2 molecule to produce a new radical C repeated steps involving production of a series of new radicals to produce RO–CF2–CF2–[CF2–CF2]n–CF2–CF2• D two radicals combine to form RO–CF2–CF2–[CF2–CF2](2n+2)–CF2–CF2–OR (i) This polymerisation can also be carried out using a non-symmetrical molecule such as CH2=CHCl to give poly(chloroethene). Write equations to show the formation of RO–CHCl–CH2• and RO–CHCl–CH2–CHCl–CH2• in stages B and C of the polymerisation of CH2=CHCl. …….………………………………………………….……………………………………………... …………………………………………………………………………………………….…….. [2] (ii) Fig. 2.1 shows a section of poly(chloroethene), where R 1 and R 2 represent chlorinated alkyl chains. Fig. 2.1 Explain why the carbon atom labelled with * is chiral. ……………………………………………………….……………………………………………... ……………………………………………………….……………………………………………... …………………………………………………………………………………………….…….. [1]

5 © Hwa Chong Institution 2024 9729/02/C2 Preliminary Examination [Turn Over (iii) Fig. 2.2 shows four repeating units within poly(chloroethene). Fig. 2.2 The free radical polymerisation of poly(chloroethene) results in different stereochemical arrangements along the carbon chain. The different arrangements can be classified into three types. Types 1 and 2 result in polymers that have regular, crystal lattice structures with higher melting points. Type 3 results in polymers that have poor packing and are unable to crystallise. By considering Fig. 2.2 and your answers to (d)(i) and (d)(ii), complete Fig. 2.3 by showing the positions of hydrogen and chlorine atoms for the three types of arrangements. Type 1 Type 2 Type 3 Fig. 2.3 [3] [Total: 13]

6 © Hwa Chong Institution 2024 9729/02/C2 Preliminary Examination [Turn Over 3 (a) Explain, with the aid of a labelled Boltzmann distribution diagram, the effect on the rate of reaction by increasing temperature. ……………………………………………………………………………………………………………… ……………………………………………………….……………...……………………………………… ……………………………………………………………………………………………………………… ……………………………………………………….……………...……………………………………… ……………………………………………………….……………………...……………………………… ……………………………………………………….……………………………...……………………… ……………………………………………………………………………………………….…………...[3] (b) Two different mechanisms for the nucleophilic substitution of halogenoalkanes are called S N1 and SN2. 2-bromopropane, a secondary bromoalkane, can undergo both SN1 and SN2. (i) Draw a mechanism for the reaction between 2 -bromopropane and OH − via SN2. Show relevant lone pairs and dipoles, and use curly arrows to indicate the movement of electron pairs. [2]

7 © Hwa Chong Institution 2024 9729/02/C2 Preliminary Examination [Turn Over (ii) Using collision theory, explain how the rate of reaction varies as the concentration of 2-bromopropane increases. ……………………………………………………….……………………………………………… ……………………………………………………….……………………………………………… ……………………………………………………….……………………………………………… ……………………………………………………….……………………………………………… ……………………………………………………….……………………………………………… …………………………………………………………………………………………….……… [2] (iii) An investigation of the kinetics of the nucleophilic substitution of 2-bromopropane with OH−