YIJC 2025 Prelim P2 (for exchange) H2 Chem

©YIJC 9729/02/JC2/PE/2025 [Turn over YISHUN INNOVA JUNIOR COLLEGE JC 2 PRELIMINARY EXAMINATION Higher 2 CANDIDATE NAME CG INDEX NO CHEMISTRY Paper 2 Structured Questions Candidates answer on the Question Paper. Additional Materials: Data Booklet 9729/02 1 September 2025 2 hours READ THESE INSTRUCTIONS FIRST Write your name, class and index number in the spaces at the top of this page. Write in dark blue or black pen. You may use an 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. This document consists of 21 printed pages and 3 blank pages. For Examiner’s Use 1 / 18 2 / 24 3 / 17 4 / 16 Penalty units significant figures Overall / 75

©YIJC 9729/02/JC2/PE/2025 2 Answer all the questions in the spaces provided. 1 (a) Compounds A, B and C are shown in order of increasing basicity. Explain this order. [3] (b) Amides can be found in many drugs such as paracetamol and procainamide. Procainamide can be used for the treatment of cardiac arrhythmias. procainamide Predict the products obtained when procainamide undergoes reaction with hot, dilute H2SO4. [2]

3 ©YIJC 9729/02/JC2/PE/2025 [Turn over (c) Compound J can be synthesised by the following route in Fig. 1.1, with all the carbon atoms coming from compound E. Fig. 1.1 • Compound E does not react with NaOH(aq) but reacts with Na to give a gas that extinguishes a lighted splint with a ‘pop’ sound. • Compound H is soluble in dilute HCl and can also be obtained from the reaction of compound K with LiAlH4. K • Compound J is neutral and is a cyclic molecule. (i) Draw the structure of compounds E to H, and J. E F G H J [5] (ii) State the reagents and conditions for steps 2 and 4. step 2 step 4 [2]

©YIJC 9729/02/JC2/PE/2025 4 (d) The compounds responsible for the umami flavour of soy sauce are salts of glutamic acid. glutamic acid Glutamic acid has pKa values of 2.1, 4.1 and 9.5. Draw the structure of the zwitterion. Suggest a pH at which the predominant species of glutamic acid is a zwitterion. [2] (e) A polypeptide contains 9 amino acid residues. It was partially hydrolysed to give a mixture of tripeptides. asp-gly-tyr glu-tyr-lys gly-glu-tyr met-asp-gly tyr-ala-gly Determine the sequence of amino acids that make up the primary structure of the polypeptide. [1]

5 ©YIJC 9729/02/JC2/PE/2025 [Turn over (f) Halogenoalkanes can react with NH2– to produce amines. A sample that contains only one enantiomer of 2 -bromobutane reacts completely with NH 2– to produce a mixture that does not rotate plane-polarised light. Draw a mechanism for the reaction between NH2– and 2-bromobutane. Include all relevant lone pairs, dipoles, curly arrows and charges. [3] [Total: 18]

©YIJC 9729/02/JC2/PE/2025 6 2 Citric acid, C6H8O7, is a naturally occurring weak organic acid found in citrus fruits. It has a wide range of applications in the food, cleaning products and healthcare industries. It is triprotic and has the following structure. (a) (i) Citric acid is a Brønsted-Lowry acid. Explain what is meant by this statement. [1] (ii) The dissociation of citric acid in water occurs in three steps. Using H3A as a simplified representation of citric acid, the first dissociation step is as shown: H3A + H2O ⇌ H2A– + H3O+ Write the balanced equation for the second dissociation step of citric acid in water. [1] (iii) Identify the two conjugate acid-base pairs in the dissociation step you have written in (a)(ii). acid conjugate base base conjugate acid [1] (iv) Explain why the carboxylic acid group on citric acid is a stronger Brønsted -Lowry acid than the hydroxyl group. [1]

7 ©YIJC 9729/02/JC2/PE/2025 [Turn over BLANK PAGE

©YIJC 9729/02/JC2/PE/2025 8 (b) The pKa values for citric acid are shown in Table 2.1. Table 2.1 pK1 pK2 pK3 citric acid 3.1 4.8 6.4 (i) Calculate the pH of 0.10 mol dm−3 citric acid at 298 K (ignore the effect of pK2 and pK3 on the pH). Show your working. [2] (ii) A buffer solution with a pH of 3.40 is made by adding 50 cm 3 of solution L containing monosodium citrate to 100 cm3 of 0.0200 mol dm−3 citric acid. Calculate the concentration of monosodium citrate in solution L. You may use NaH2A to represent monosodium citrate, and H3A to represent citric acid. [3]

9 ©YIJC 9729/02/JC2/PE/2025 [Turn over (iii) Using an equation, explain how the citric acid/monosodium citrate buffer solution in (b)(ii) resists pH changes when a small amount of acid is added to it. [2] (iv) 10 cm3 of 0.100 mol dm−3 citric acid was titrated against 0.100 mol dm−3 sodium hydroxide. The titration curve is shown in Fig. 2.1. Fig. 2.1 Fill in the boxes above with the correct pH values and NaOH volumes. [2] pH volume of NaOH added / cm3

©YIJC 9729/02/JC2/PE/2025 10 (c) A sample of citric acid is heated with excess ethanol in the presence of a small amount of concentrated sulfuric acid. (i) In the box above, draw the skeletal structure of the organic product formed. [1] (ii) State the type of reaction that has occurred. [1] (d) Citric acid can be synthesised from glycerol in 5 steps according to the following reaction scheme. (i) Step 1 is a nucleophilic substitution reaction. Using specific reagents and conditions, only the primary alcohol groups of glycerol are substituted to produce a chloroalkane. Suggest why substitution occurs only at the primary alcohol groups. [1]