2022 HCI H2 Chemistry Promo P2 QP

This document consists of 12 printed pages. HWA CHONG INSTITUTION C1 Promotional Examination Higher 2 CANDIDATE NAME CT GROUP 22S CHEMISTRY Paper 2 Structured Questions Candidates answer on the Question Paper. Additional Materials: Data Booklet 9729/02 28 September 2022 1 h 5 min READ THESE INSTRUCTIONS FIRST Write your name and CT group on all the work you hand in. Write in dark blue or black pen. You may use a soft pencil for diagrams and graphs only. 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 EXAMINERS’ USE ONLY Paper 1 (24%) Paper 2 (39%) Paper 3 (37%) TOTAL Q1 / 11 Q1 / 20 Q2 / 18 Q2 / Q3 / 15 Q3 / 11 Deductions (s.f.) Deductions (total) Deductions (units) / 20 / 40 / 35 100

2 © Hwa Chong Institution 2022 9729/02/C1 Promotional Exam 2022 [Turn over 1 Iron is the f ourth most abundant element on E arth. It is essential to all living things and has widespread industrial application. DO NOT WRITE IN THIS MARGIN (a) Describe the bonding in iron with the aid of a labelled diagram. ..………………………..……….…………………………………………………….……….…………… ..…………………………...…………………………………………………………….…….…………… ..……………………….…..…………………………………………………………….…….…………… ..…………………………....…………………………………………………………….…….……….. [2] (b) Iron, copper and zinc can be found in Period 4 of the Periodic Table. (i) Complete the electronic configurations of Cu+ and Zn+. Cu+: 1s2 2s2 2p6 ……………………………………..……………… Zn+: 1s2 2s2 2p6 ……………………………………..……………… [2] (ii) With reference to your answer in (b)(i), suggest why the second ionisation energy of copper is higher than that of zinc. ……………………………………………………………………………….….……….…………… ……………………………………………………………………………….….……….…………… ……………………………………………………………………………….….……….…………… ……………………………………………………………………………….….……….…………… ……………………………………………………………………………….….……….…………… ……………………………………………………………………………….….……….…………… ………………………………….………………………………………………….…….…………… ………………………………………….……………………………………….………………… [2]

3 © Hwa Chong Institution 2022 9729/02/C1 Promotional Exam 2022 [Turn over (c) Finely divided iron is used industrially as a catalyst in the Haber process to manufacture ammonia from nitrogen gas and hydrogen gas. The Haber process is typically carried out at 450 °C and 200 atm. N2(g) + 3H2(g) ˆ ˆ †‡ ˆ ˆ 2NH3(g) Hr = −92.0 kJ mol−1 DO NOT WRITE IN THIS MARGIN (i) By considering the rate of reaction and position of equilibrium, e xplain why a moderately high temperature of 450 °C is used for the Haber process. ………………………………………………………………………………………..…….………… ……………………………………………………………………………………….…..…………… ……………………………………………………………………………………….…..…………… ………………………………………………………………………………………..….…………… ………………………………………………………………………………………..…………… [2] Ammonia is one of the most highly produced inorganic chemicals. For the process, nitrogen gas is obtained from the air which contains 78.08% nitrogen gas by volume. (ii) The current global output of ammonia is 3300 tonnes of ammonia per day. Calculate the volume of nitrogen gas required for the reaction per day, given that the yield of the reaction is 15%. Assume all gases are measured at room temperature and pressure. (1 tonne = 1000 kg) [2] (iii) Hence, calculate the volume of air consumed for the reaction daily. [1] [Total: 11]

4 © Hwa Chong Institution 2022 9729/02/C1 Promotional Exam 2022 [Turn over 2 (a) (i) But-1-ene reacts with hydrogen bromide to form 2-bromobutane. Describe the mechanism of the reaction of b ut-1-ene with HBr to form 2-bromobutane, showing curly arrows, charges, dipoles and any relevant lone pairs. [3] DO NOT WRITE IN THIS MARGIN (ii) Explain what is meant by the term bond energy. …………………………………………….…………………………………….……….…………… …………………………………………….………………………………………….…………… [1] (iii) Use appropriate bond energy data from the Data Booklet to calculate a value for the standard enthalpy change of the reaction in (a)(i). ∆H = …………………………………………. [2]

5 © Hwa Chong Institution 2022 9729/02/C1 Promotional Exam 2022 [Turn over (iv) Explain what is meant by the term activation energy. DO NOT WRITE IN THIS MARGIN …………………………………….………………………………………………….……….……… …………………………………….………………………………………………………….…… [1] (v) On the axes in Fig 2.1, construct an energy profile diagram for the reaction of but-1-ene with HBr to form 2-bromobutane. Label clearly the axes, the carbocation intermediate, the activation energies and the ∆H you calculated in (a)(iii). Fig. 2.1 [2] (vi) The reaction between but -1-ene and hydrogen bromide produces 2-bromobutane rather than 1-bromobutane. Explain why 2-bromobutane is the product formed rather than 1-bromobutane. ………………………………………….…………………………………………….…….………… …………………………………………………….………………………………….…….………… …………………………………………………….………………………………….……….……… ………………………………………………………………………………………….…….…… [2]

6 © Hwa Chong Institution 2022 9729/02/C1 Promotional Exam 2022 [Turn over (b) Butadiene also reacts with hydrogen bromide. When they react in a 1:1 mole ratio, a mixture of products, A and B, are formed, as shown in Fig 2.2. Fig. 2.2 DO NOT WRITE IN THIS MARGIN (i) Both products A and B are formed via the same carbocation intermediate, C. The bromide anion, Brˉ, can either attack carbon-1 or carbon-3 on carbocation C to give A or B, respectively. This is because the positive charge on carbocation C is delocalised across carbon-1, carbon-2 and carbon-3. Carbon-1, carbon-2 and carbon-3 are sp2 hybridised. Explain why delocalisation is possible across these three carbon atoms. ………………………………….…………….………………………………………….…………… ………………………………….…………….………………………………………….…………… …………………………………….………….…………………………………………………… [1]

7 © Hwa Chong Institution 2022 9729/02/C1 Promotional Exam 2022 [Turn over (ii) For each product A and B respectively, state the number of each type of carbon -carbon σ bonds present in Table 2.1. DO NOT WRITE IN THIS MARGIN Table 2.1 carbon-carbon σ bonds product A product B number of sp2‒sp2 bonds number of sp2‒sp3 bonds number of sp3‒sp3 bonds [1] (iii) The strengths of the carbon-carbon σ bonds in Table 2.1 increase in the following order. sp3‒sp3 < sp2‒sp3 < sp2‒sp2 Explain why. …………………………………….………………………………………………….……….……… …………………………………….………………………………………………….…….………… …………………………………….……………………………………………………….……… [1] (iv) Alkenes which have stronger covalent bonds are more stable. Using your answers in (b)(ii) and (b)(iii), explain whether A or B is more stable. …………………………………….……………………………………………….…….…………… …………………………………….……………………………………………….……………… [1]

8 © Hwa Chong Institution 2022 9729/02/C1 Promotional Exam 2022 [Turn over (c) When heated at a high temperatur