YIJC 2025 Prelim P3 (for exchange) H2 Chem

©YIJC 9729/03/JC2/PE/2025 [Turn over YISHUN INNOVA JUNIOR COLLEGE JC 2 PRELIMINARY EXAMINATION Higher 2 CANDIDATE NAME CG INDEX NO CHEMISTRY Paper 3 Free Response Candidates answer on the Question Paper. Additional Materials: Data Booklet 9729/03 16 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. If additional space is required, you should use the pages at the end of this booklet. The question number must be clearly shown. Section A Answer all questions. Section B Answer one question. A Data Booklet is provided. The use of an approved scientific calculator is expected, where appropriate. 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. This document consists of 28 printed pages. For Examiner’s Use Section A 1 / 17 2 / 18 3 / 25 Section B 4 or 5 / 20 Penalty units significant figures Overall / 80

©YIJC 9729/03/JC2/PE/2025 2 Section A Answer all the questions in the spaces provided. 1 (a) Explain, with the aid of a labelled Boltzmann distribution diagram, the effect on a rate constant of increasing temperature from T1 to T2. [3]

3 ©YIJC 9729/03/JC2/PE/2025 [Turn over (b) Hydrogen bromide, HBr, undergoes addition reaction with alkenes. With but-1-ene, 2-bromobutane is produced rather than 1-bromobutane. (i) Draw a mechanism for this reaction and use it to explain the preferential production of 2-bromobutane. [3] (ii) Using the mechanism, write the rate equation for this reaction. [1] (iii) Sketch a graph to show how the rate of reaction varies with the concentration of but -1-ene when hydrogen bromide is in excess. Explain your answer. [2]

©YIJC 9729/03/JC2/PE/2025 4 (c) But-2-ene is a positional isomer of but-1-ene. But-2-ene occurs in two isomeric forms, A and B. (i) Explain how A and B are stereoisomers of each other but but -1-ene does not show stereoisomerism. [2] (ii) Describe a chemical test, with appropriate observations, that could distinguish between but-1-ene and but-2-ene. [2] (d) But-1-ene can be converted into an ether (–C–O–C–) via the steps shown in Fig. 1.1. Fig. 1.1 In step 1, an epoxide functional group is formed when a n O atom adds across the double bond through reaction with m-CPBA. In step 2, t he epoxide formed reacts with sodium methoxide, a nucleophile , to form an ether functional group (–C–O–C–).

5 ©YIJC 9729/03/JC2/PE/2025 [Turn over (i) The resulting mixture of the ether contains equal quantities of two isomers. The mixture does not rotate plane-polarised light. Draw the three-dimensional structures of these two isomers. [2] (ii) Suggest the structure of the ether formed when but-2-ene is subjected to the same reaction as in Fig. 1.1. [1] (iii) A primary amine can also be used as the nucleophile in step 2, but the final product will be a secondary amine, as shown in Fig. 1.2, instead of an ether. Fig. 1.2 Suggest the structure of alkene C. [1] [Total: 17]

©YIJC 9729/03/JC2/PE/2025 6 2 (a) Compound D has molecular formula CxHyOz. Its relative molecular mass is 90.0. When 2.25 g of D was burnt in excess oxygen, 4.40 g of CO2 and 2.25 g of H2O were obtained. Calculate the empirical formula of D and determine its molecular formula. [4]

7 ©YIJC 9729/03/JC2/PE/2025 [Turn over (b) D can undergo controlled oxidation to form E (C4H6O2). E can be further oxidised to form F (C4H6O3). No oxygen atoms are present in the carbon backbone of E and F. Four chemical tests are carried out on portions of E and F and the results are described in Table 2.1. Table 2.1 with Na2CO3(aq) with Tollens’ reagent with 2,4-DNPH with alkaline I2(aq) E no reaction silver mirror orange precipitate no reaction F effervescence no reaction orange precipitate no reaction Deduce the displayed structures of E and F. [5]

©YIJC 9729/03/JC2/PE/2025 8 (c) G, a constitutional isomer of F, is a -keto acid that readily loses CO2 upon heating in a process known as decarboxylation, as shown in Fig. 2.1. An enol is formed as an intermediate. The enol undergoes keto-enol tautomerism almost immediately to form the ketone. decarboxylation keto-enol tautomerism Fig. 2.1 (i) Explain what is meant by constitutional isomerism. [1] (ii) Complete the mechanism for decarboxylation on Fig. 2.1 by adding curly arrows. [1] (iii) Suggest the structure of the -keto acid that would give 3-phenylbutan-2-one upon heating. [1]

9 ©YIJC 9729/03/JC2/PE/2025 [Turn over (d) (i) Some ionic radii are listed in the Data Booklet. State and explain the differences between the ionic radii of Na, Si and P. [3] (ii) Describe the reactions, if any, of the oxides Na 2O, SiO 2 and P 4O10 with water. Write an equation for any reaction and state the pH of the resultant mixtures. [3] [Total: 18]

©YIJC 9729/03/JC2/PE/2025 10 3 (a) Chromium, a transition metal, is widely used in stainless steel production for its corrosion resistance. (i) State the electronic configurations of a Cr atom and of a Cr3+ cation. [2] (ii) Describe two ways in which compounds containing Cr 3+ ions are different from those containing Ca2+ ions in terms of their chemical behaviour. [2] (b) Chromium(III) bromide, CrBr3, is a dark-coloured solid used in chemical synthesis and research, particularly for studying magnetic and electronic properties of transition metal halides. (i) Define the term lattice energy. [1] (ii) Use data from Table 3.1 and the Data Booklet to calculate a value for the lattice energy of CrBr3(s). Show your working. [3] Table 3.1 value/kJ mol─1 first electron affinity of bromine −324.6 standard enthalpy change of vapourisation of bromine molecules +29.6 standard enthalpy change of atomisation of chromium +397 standard enthalpy change of formation of CrBr3(s) −400.4 (iii) Chromium(III) bromide and chromium(III) iodide have the same crystal structure. There is closer agreement between the experimental and theoretical values of lattice energy for CrBr3 than for CrI3. Suggest a reason for this. [1]