2017 HCI H1 Chemistry Prelims P2 Questions

This document consists of 11 printed pages (including this cover page) HWA CHONG INSTITUTION C2 Preliminary Examinations Higher 1 CANDIDATE NAME CT GROUP 16S CENTRE NUMBER INDEX NUMBER CHEMISTRY Paper 2 Candidates answer Section A on the Question Paper. Additional Materials: Answer paper Data Booklet Graph paper (2 sheets) 8872/02 11 September 2017 2 hours READ THESE INSTRUCTIONS FIRST Write your Centre number, index number and name on all the work you hand in. Write in dark blue or black pen. You may use a pencil for any diagrams, graphs or rough working. Do not use staples, paper clips, highlighters, glue, correction fluid or tapes. The use of an approved scientific calculator is expected, where appropriate. Section A Answer all the questions. Section B Answer two questions on separate answer paper. 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. FOR EXAMINERS’ USE ONLY TOTAL Multiple Choice Section A (Structured) Section B (Free Response) Q1 / 20 Q4 / 20 Q2 / 10 Q5 / 20 Q3 / 10 Q6 / 20 / 30 Subtotal / 40 Subtotal / 40 110

2 2017 HCI Preliminary Examination H1 Chemistry Paper 2 Section A Answer all the questions in this section in the spaces provided. 1 (a) Nitrogen and hydrogen react together to form ammonia in the Haber process. N2(g) + 3H2(g) ⇌ 2NH3(g) H = – 92 kJ mol–1 Industrially, the following conditions are used for the Haber process. pressure 250 atm temperature 450 ˚C catalyst finely divided iron catalyst (i) With the aid of Le Chatelier’s Principle, explain why a moderate temperature of 450 oC is used for the Haber process. ……………………………………………………………………………………………. ……………………………………………………………………………………………. ……………………………………………………………………………………………. ……………………………………………………………………………………………. ………………………………………………………………………………………… [2] (ii) Explain how iron catalyst can increase the rate of formation of ammonia. ……………………………………………………………………………………………. ………………………………………………………………………………………… [1] (iii) State and e xplain the effect of using a pressure of 400 atm on the position of equilibrium and the equilibrium constant. ……………………………………………………………………………………………. ……………………………………………………………………………………………. ……………………………………………………………………………………………. ……………………………………………………………………………………………. ………………………………………………………………………………………… [2]

3 2017 HCI Preliminary Examination H1 Chemistry Paper 2 Given that 4 moles of N2 and 8 moles of H2 are allowed to reach dynamic equilibrium in a 2 dm3 vessel. It is found that the total number of moles of gases present in the vessel at equilibrium is 8. (iv) Write a Kc expression for the equilibrium in the formation of ammonia. [1] (v) Calculate the number of moles of each gas at equilibrium, showing your workings clearly. number of moles of N2: …………...mol; H2: …………...mol NH3: …………...mol [2] (vi) Hence, calculate the equilibrium constant and state its units. Kc = ……………………. units = …………………… [2]

4 2017 HCI Preliminary Examination H1 Chemistry Paper 2 (b) (i) Ammonia burns in oxygen to give nitrogen dioxide and steam. Write an equation, with state symbols, which represents the enthalpy chan ge of combustion of ammonia. ………………………………………………………………………………………… [1] (ii) Hence, use the following information to calculate a value for the enthalpy change of combustion of ammonia. Enthalpy change of formation of nitrogen dioxide - 34 kJ mol-1 Enthalpy change of formation of steam - 242 kJ mol-1 Enthalpy change of formation of ammonia - 46 kJ mol-1 [2] (iii) Using relevant information from the Data Booklet as well as your answer in b(ii), calculate a value for the bond energy of the bond between the nitrogen atom and the oxygen atom in nitrogen dioxide, assuming that the bond energy of both bonds are the same. bond energy: ……………………. kJ molˉ1 [2] (iv) The combustion of 44 g of ammonia produces 89 g of nitrogen dioxide. Calculate the percentage efficiency of this reaction. [2]

5 2017 HCI Preliminary Examination H1 Chemistry Paper 2 (c) Ammonia reacts with bromoethane. Write an equati on for the reaction that occurs and g ive the reagent and c onditions necessary. State fully which class of organic compound the product belongs to. Equation: ……………………………………………………………………………………….. Reagents and conditions: ………………………………………………………..……………. Class of organic compound: ………………………………………………………………. [3] [Total: 20]

6 2017 HCI Preliminary Examination H1 Chemistry Paper 2 2 This question is about Period 3 elements and their compounds. (a) Period 3 elements react with oxygen to form oxides. (i) Describe the reaction of aluminium oxide and phosphorus(V) oxide with hydrochloric acid and sodium hydroxide, if any. ……………………………………………………………………………………………. ………………………………………………………………………………………… [2] (ii) Write equations for all reactions that occur in (b)(i). aluminium oxide: …….…………………………………………………………………. ……………………………………………………………………………………………. phosphorus oxide: ……………………………………………………………………… ………………………………………………………………………………………….… [3] (b) (i) In the vapour phase, an equilibrium is established between aluminium chloride and its dimer as follows: 2AlCl3(g) Al2Cl6(g) With the aid of a diagram, explain how the dimer is formed. ……………………………………………………………………………………………. ……………………………………………………………………………………………. ……………………………………………………………………………………………. ………………………………………………………………………………………… [3] (ii) At 180 oC, aluminium chloride, Al2Cl6, sublimes. Explain, based on its structure and bonding, why it sublimes at a relatively low temperature. ……………………………………………………………………………………………. ……………………………………………………………………………………………. ………………………………………………………………………………………… [2] [Total: 10]

7 2017 HCI Preliminary Examination H1 Chemistry Paper 2 3 The following diagram shows some reactions of methylbenzene. (a) State the reagents and conditions necessary for Step 1. Reagents and conditions: …………………………………………………………………[1] (b) State the types of reaction for Steps 2 and 3. Step 2: ……………………………………………………………………………………….….. Step 3: …………………………………………………………………………………………... [2] (c) Explain why B is acidic. …………………………………………………………………………………………………… …………………………………………………………………………………………………… …………………………………………………………………………………………..…… [2]

8 2017 HCI Preliminary Examination H1 Chemistry Paper 2 The structures of D and E are shown again below for parts (d) and (e). (d) There is another method to obtain D from methylbenzene in one step. Give the reagents and conditions for this method and explain why this method is not preferred. Reagents and conditions: …………………………………………………………………….. …………………………………………………………………………………………………… …………………………………………………………………………………………..…… [2] (e) Propose a 2 -step synthesis for the conversion of D to E. Give the reagen ts and conditions for all steps and the structure of any intermediate. [3] [Total: 10]

9 2017 HCI Preliminary Examination H1 Chemistry Paper 2 Section B Answer two questions from this section on separate answer paper. 4 (a) In the production of instant noodles, a key step involves deep frying the noodles in cooking oil to remove all traces of moisture. By dehydrating the noodles in this manner, the shelf life of the product increases dramatically. (i) Cooking oil is primarily made up of long hydrocarbon chains, and has an approximate boiling point of 300 °C, whereas water has a boiling point of 100 °C. Explain why cooking oil has a higher boiling poin