2022 HCI Prelim P2 Question Paper

This document consists of 17 printed pages and 2 blank pages. HWA CHONG INSTITUTION C2 Preliminary Examinations Higher 2 CANDIDATE NAME CT GROUP 21S CENTRE NUMBER INDEX NUMBER CHEMISTRY Paper 2 Structured Questions Candidates answer on the Question Paper Additional Materials: Data Booklet 9729/02 29 August 2022 2 hours READ THESE INSTRUCTIONS FIRST Write your name, CT group, centre number and index number clearly in the spaces above. 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 in the Question Paper. The use of an approved scientific calculator is expected, where appropriate. A Data Booklet is provided. 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 Examiner’s Use 1 / 11 2 / 9 3 / 13 4 / 15 5 / 27 Deductions Total / 75

2 © Hwa Chong Institution 2022 9729/02/C2 Preliminary Exam [Turn over Answer all the questions in the spaces provided. DO NOT WRITE IN THIS MARGIN 1 Fossil fuels which are found in deposits have been formed from plants and animals that lived millions of years ago. When fossil fuels are burned in internal combustion engines, CO 2 and H 2O are the main products, with NO and SO2 also being formed. (a) (i) What class of compound, present in fossil fuels, produces CO 2 and H 2O on combustion? ……………………………………………………………………………………………….[1] (ii) NO and NO 2, collectively known as oxides of nitrogen, are pollutants that are also formed during combustion in motor vehicles. Write equations to show how each of these two gases are formed in vehicle engines. …………………………………………………………………………………………………. ………………………………………………………………………………………..……..[1] (iii) State one harmful effect of oxides of nitrogen on the environment. ……………………………………………………………………………………………….[1] To meet emission standards in Singapore, sulfur emissions from cars have to be lower than 50 parts per million (ppm). This means that there should be less than 50 molecules of SO 2 for every 1 × 106 molecules of gas in the fuel exhaust for it to meet regulations. (b) (i) A sample of fuel was combusted at 900 C and 10.0 bar. At the end of the reaction, 63.2 dm3 of gas was collected under the same conditions. Determine the amount of gas, in moles, produced by combustion of the fuel sample. [2] (ii) Given that 0.0183 g of SO2 was produced in (b)(i), calculate the concentration of SO2, in parts per million, and explain whether the fuel exhaust meets the sulfur emission standards. [2]

3 © Hwa Chong Institution 2022 9729/02/C2 Preliminary Exam [Turn over (c) Describe the reactions, if any, of SO3, Na2O and Al2O3 with water. Include the approximate pH value of any resulting solutions, and write equations for any reactions that occur. ……………………………………………………….……………………………………………… ……………………………………………………….……………………………………………… ……………………………………………………….……………………………………………… ……………………………………………………….……………………………………………… ……………………………………………………….……………………………………………… ……………………………………………………….……………………………………………… ……………………………………………………….……………………………………………… ……………………………………………………….……………………………………………… ……………………………………………………….……………………………………………[4] [Total: 11] DO NOT WRITE IN THIS MARGIN

4 © Hwa Chong Institution 2022 9729/02/C2 Preliminary Exam [Turn over 2 Monosodium glutamate (MSG ) is a natural flavour enhancer present in foods. Natural ly occurring MSG can be extracted from seaweed and is commonly manufactured on a large scale by fermenting sugars. MSG DO NOT WRITE IN THIS MARGIN (a) (i) A chemist proposed to synthesis e MSG using the following reaction scheme. Draw intermediates A and B, and state the reagents and conditions for step 1 and step 2. Fig. 2.1 step 1: .………………………..……………….………...……………………………………. step 2: ..………………………..……………….………………………………...…………… [4] (ii) In the final step of the reaction scheme, the –CyO2H group is deprotonated instead of the –CxO2H group. Explain why this is so. ……………………………………………………….………………………………………… ……………………………………………………….………………………………………… ……………………………………………………….………………………………………… ……………………………………………………….………………………………………… ……………………………………………………….………………………………………[2] step 1 step 2 A B NH3, heat in sealed tube

5 © Hwa Chong Institution 2022 9729/02/C2 Preliminary Exam [Turn over (iii) Food flavours enhanced by the MSG synthesised in the laboratory according to Fig. 2.1 might taste differently from flavours enhanced by natural ly occurring MSG. Suggest why this is so. DO NOT WRITE IN THIS MARGIN ……………………………………………………….………………………………………… ……………………………………………………….………………………………………… ……………………………………………………….………………………………………… ……………………………………………………….………………………………………… ……………………………………………………….………………………………………[1] (b) High sodium content food is linked to increased risk of heart disease. Some health experts recommend using MSG instead of table salt (NaCl) to flavour food so as to reduce sodium intake. With the aid of suitable calculations, show that 1 g of MSG helps achieve lower sodium intake than 1 g of table salt. [2] [Total: 9]

6 © Hwa Chong Institution 2022 9729/02/C2 Preliminary Exam [Turn over BLANK PAGE

7 © Hwa Chong Institution 2022 9729/02/C2 Preliminary Exam [Turn over 3 The structures of amino acids A to D are given below. DO NOT WRITE IN THIS MARGIN (a) Identify the amino acid that is not an α-amino acid. ..………………………..………………………………………………………………………… [1] (b) On complete hydrolysis, a tripeptide gave the other three amino acids not identified in (a) in equimolecular amounts. Draw the structural formula of one such tripeptide at pH 1 and pH 14. At pH 1: At pH 14: [3]

8 © Hwa Chong Institution 2022 9729/02/C2 Preliminary Exam [Turn over (c) The pKa values of the acidic groups in a fully protonated arginine are labelled below. fully protonated arginine DO NOT WRITE IN THIS MARGIN (i) Given that N x and Ny are both sp2 hybridised, suggest why they are both very weak bases. ..………………………..……………….……………………………………………………... ..………………………..……………….……………………………………………………... ..………………………..…………………………………………………………………... [1] When a 10.0 cm3 sample of the fully protonated arginine is titrated against 0.100mol dm–3 NaOH, the following titration curve is obtained. Fig. 3.1 (ii) Calculate the concentration of arginine in the 10.0 cm3 sample. [1] pH Volume of NaOH(aq) / cm3 0 10 20 30 40 50 60 P Q × ×

9 © Hwa Chong Institution 2022 9729/02/C2 Preliminary Exam [Turn over (iii) Calculate the pH of the solution at point P (ignore the effects of the second and third acid dissociations on the pH). [2] DO NOT WRITE IN THIS MARGIN (iv) Determine the pH at point Q. [1] (v) Explain, using an equation and the relevant ionic forms of arginine, why the pH changes only gradually around point Q as aqueous NaOH is added. ..………………………..……………….……………………………………………………... ..………………………..……………….……………………………………………………... ..………………………..……………….……………………………………………………... ..………………………..……………….……………………………………………………... ..…………