DHS 2026 Prelim P3 Ans

This document has 29 pages. Any blank pages are indicated. © DHS 2026 [Turn over Suggested Solutions with Marker’s Comments DUNMAN HIGH SCHOOL Preliminary Examination Year 6 H2 CHEMISTRY Paper 3 Structured Questions You must answer on the question paper. You will need: Data Booklet 9476/03 17 September 2026 2 hours INSTRUCTIONS • Section A: answer all questions. • Section B: answer one question. • Use a black or dark blue pen. You may use an HB pencil for any diagrams or graphs. • Write your name, centre number and index number in the boxes at the top of the page. • Write your answer to each question in the space provided. • Do not use an erasable pen. Do not use correction fluid or tape. • You may use an approved calculator. INFORMATION • The total mark for this paper is 75. • The number of marks for each question or part question is shown in brackets [ ]. For Examiner’s Use 1 18 2 18 3 19 4 20 5 20 Total 75

2 © DHS 2026 9476/03 Section A Answer all the questions in this section in the spaces provided. 1 (a) Succinimide is a white solid used in a variety of organic syntheses. It is classified as a cyclic imide. An imide is a functional group consisting of two acyl groups bonded to nitrogen. NH O O succinimide Compound M can be converted to form succinimide via condensation according to reaction 1. O O O NH O O + NH3 + H2O M Explain why cyclic imides are generally much more acidic than amides. [1] The negative charge on the nitrogen atom in the conjugate base of cyclic imides is delocalised over two oxygen atoms of the carbonyl groups, hence, resonance stabilising the anion and increasing the acidity. reaction 1

3 © DHS 2026 9476/03 [Turn Over (b) Torlon® is a type of commercial polyamide-imide (PAI) polymer known for its exceptional toughness. Monomers X (4,4’-diaminodiphenylmethane) and Y (trimellitic anhydride chloride) can be used to synthesise Torlon®. NH2 NH2 Cl O O O O X Y (i) With reference to reaction 1, draw the product that contains an imide linkage, formed from one molecule of X and one molecule of Y. You may use R to represent . [1] N O O O R NH2 Cl (ii) Torlon® is a type of PAI polymer since it consists of three types of repeat units containing different types of linkages that can be formed between monomers of X and Y. The different types of linkages are:  amide-imide  imide-imide  amide-amide Draw a possible section of Torlon® that contains all three types of repeat units. Label each type clearly. You may use R to represent . [3]

4 © DHS 2026 9476/03 (iii) Tensile strength is the maximum force that is applied to a material before it breaks. Explain, in terms of bonding, why Torlon® is said to be rigid and has an exceptional tensile strength. [1] The amide groups in the structure form extensive hydrogen bonding between adjacent polymer chains. OR The backbone consists of predominantly aromatic rings and alternating imide/amide linkages, which restrict chain mobility/ chain rotation and enhance stiffness. (c) Phenylamine is used to synthesise X via a multi-step process. (i) Phenylamine can be made from nitrobenzene. Describe the reagents and conditions required to form phenylamine from nitrobenzene. [1] Sn and concentrated HCl with heating, followed by NaOH(aq) (ii) Phenylamine and two other nitrogen-containing compounds, A and B, are shown in order of increasing basicity. Explain this order. A B [3] A is less basic than phenylamine as the electron-withdrawing Cl atom decreases the electron density on the N atom in A, making the lone pair of electrons on N less available for donation to a proton. NO2 NH2 NH2 Cl NH2 NH2 amide-imide imide-imide amide-amide < <

5 © DHS 2026 9476/03 [Turn Over Phenylamine is less basic than B as the lone pair of electrons on N is delocalised into benzene ring and is less available for donation to a proton. Moreover, the electron-donating C6H11−/ cyclohexyl group increases the electron density on the N atom in B, making the lone pair of electrons on N more available for donation to a proton. (d) Fig. 1.1 shows the structure of chloroethene, also known as vinyl chloride monomer (VCM). Fig. 1.1 (i) Explain why chloroethene undergoes hydrolysis much less readily than chloroethane. [2] The p orbital of the chlorine atom overlaps side -on with the p orbitals of the two carbon atoms of the C-C double bond/ -C=C-. Lone pair of electrons in the p -orbital of the chlorine atom delocalise into the adjacent  bond, resulting in a partial double bond character in the C–Cl bond. Therefore, more energy is required to break the stronger C–Cl bond. (ii) VCM is used to manufacture polyvinyl chloride (PVC), an addition polymer used in pipes and construction materials. Draw the structure of PVC. Show at least two repeat units. [1] C C H H Cl C H H C H ClH (iii) Comment on the biodegradability of PVC. [1] PVC is chemically inert and can therefore be difficult to biodegrade. (e) Enzymes are proteins that act as biological catalysts with high specificity. (i) Define proteins. [1] Proteins are condensation polymers made of monomers called α−amino acids forming peptide bonds. (ii) Using the lock -and-key model, describe how enzymes function as biological catalysts with high specificity. You may want to include labelled diagrams in your answer. [2] C C H H Cl H

6 © DHS 2026 9476/03 Step Description 1 Enzymes p rovide an alternative pathway with lower activation energy for reaction to take place. Enzymes contain specific region known as active site with shape that is strictly complementary to the shape of its specific substrate/ reactant. Substrate arrives at active site of enzyme. 2 Substrate fits into active site where rearrangement of molecules occurs to form products. 3 Products leave active site. Once products are formed, they no longer fit into the active site and escape into the surrounding medium, leaving the active site free to receive further substrate molecule. (iii) The hydrolysis of lactose , a sugar found in milk, is catalysed by the enzyme lactase. Under low lactose concentration, the reaction follows first-order kinetics. Sketch a concentration of lactose versus time graph for a first-order reaction and indicate on your sketch, how successive half-lives vary. [1] [Total: 18]

7 © DHS 2026 9476/03 [Turn Over 2 The production of synthetic fragrances often begins with short -chain alkanes obtained from petroleum. One such process involves the chlorination of 2-methylbutane to produce a mixture of chloroalkanes, which are then converted into alkenes for further functionalisation. (a) 2-methylbutane, CH 3CH(CH3)CH2CH3, reacts with limited chlorine in the presence of ultraviolet light to form a mixture of four structural isomers with the m