JPJC Prelim 2025 Paper 2 QP H2 Chem

© Jurong Pioneer Junior College [Turn Over NAME CLASS 24S JURONG PIONEER JUNIOR COLLEGE JC2 PRELIMINARY EXAMINATION 2025 CHEMISTRY 9729/02 Paper 2 Structured Questions 29 August 2025 2 hours Candidates answer on the Question Paper. Additional Materials: Data Booklet 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 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 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. For Examiner’s Use 1 16 2 11 3 14 4 18 5 16 Penalty (delete accordingly) Lack 3sf in final answer –1 / NA Missing/wrong units in final ans –1 / NA Bond linkages –1 / NA Total 75 This document consists of 20 printed pages.

2 © Jurong Pioneer Junior College 9729/02/J2 PRELIMINARY EXAM/2025 Answer ALL the questions in the spaces provided. 1 Nitrogen is found in inorganic compounds such as the oxides of nitrogen, NO 2 and NO. For Examiner’s Use (a) NO2 can be produced from the thermal decomposition of gaseous N2O5. 2N2O5(g) → 4NO2(g) + O2(g) H1 Table 1.1 gives some data relevant to this question. Table 1.1 process H / kJ mol−1 standard enthalpy change of formation of N2O5(g) +11.3 standard enthalpy change of formation of NO(g) +89.0 NO(g) + 1 2 O2(g) → NO2(g) −58.1 (i) Explain what is meant by standard enthalpy change of formation. ……………………………………………………………………………………. ……………………………………………………………………………………. ……………………………………………………………………………………. [1] (ii) Use data from Table 1.1 to calculate H1. You may find it helpful to draw an energy cycle. [2]

3 © Jurong Pioneer Junior College 9729/02/J2 PRELIMINARY EXAM/2025 [Turn Over (iii) In the solid state, N 2O5 has an ionic structure and consists of the ions, NO2+ and NO3−. Draw and name the shapes of NO2+ and NO3−. For Examiner’s Use ion NO2+ NO3− diagram of shape name of shape [3] (b) Nitrogen dioxide, NO 2, and dinitrogen tetraoxide, N 2O4, exist in dynamic equilibrium with each other. N2O4(g) = 2NO2(g) H = +58 kJ mol−1 At 50 C and a pressure of 1.68  105 Pa, 4.60 g of the equilibrium gaseous mixture occupies 1.00 dm3. (i) Assuming the gaseous mixture behaves ideally, calculate the average relative molecular mass, Mr, of the gaseous mixture. [1] (ii) Using the following relationships, calculate the mole fraction of N 2O4, m, and the mole fraction of NO2, n, in the mixture. m + n = 1 Average Mr = 92m + 46n [1]

4 © Jurong Pioneer Junior College 9729/02/J2 PRELIMINARY EXAM/2025 (iii) Hence calculate the partial pressures of N2O4 and NO2 in the mixture. For Examiner’s Use [1] (iv) Write an expression for equilibrium constant, Kp, for the reaction, and calculate its value. Include units in your answer. [3] (v) State and explain the effect of increasing the temperature on the average Mr of the equilibrium mixture. ……………………………………………………………………………………. ……………………………………………………………………………………. ……………………………………………………………………………………. ……………………………………………………………………………………. ……………………………………………………………………………………. [2] (c) With the aid of suitable equations, describe and explain the role of NO 2 in the oxidation of atmospheric sulfur dioxide. …………………………………………………………………………………………... ……………………………………………………………………………………..……. …………………………………………………………………………………………... …………………………………………………………………………………………... [2] [Total: 16]

5 © Jurong Pioneer Junior College 9729/02/J2 PRELIMINARY EXAM/2025 [Turn Over 2 Copper(I) salts in aqueous solution are unstable as shown by equation 1. equation 1 2Cu+(aq) → Cu(s) + Cu2+(aq) For Examiner’s Use (a) (i) Using relevant data from the Data Booklet, calculate G, in kJ mol−1, for the above reaction. [2] (ii) Deduce the sign of S for the reaction and explain your answer. ……………………………………………………………………………………. ……………………………………………………………………………………. ……………………………………………………………………………………. [1] (iii) Hence, determine if the reaction in equation 1 is exothermic or endothermic. Explain your answer. ……………………………………………………………………………………. ……………………………………………………………………………………. ……………………………………………………………………………………. ……………………………………………………………………………………. [1]

6 © Jurong Pioneer Junior College 9729/02/J2 PRELIMINARY EXAM/2025 (b) Some copper(I) compounds are used as reagents in organic reactions where new carbon -carbon bonds are formed . Larger alkanes can also be formed through the reaction of alkanes with some halogens. However, the yield of the larger alkanes obtained through such a reaction is low. For Examiner’s Use (i) Trace amount of alkane A is obtained when 2-methylpropane reacts with bromine in the presence of ultraviolet light. A Outline the mechanism of this reaction, clearly showing how A is formed in the above reaction. [3] (ii) Chloroalkanes can be formed by the above mechanism but not iodoalkanes. Use relevant data from the Data Booklet to explain why iodoalkanes cannot be formed. ……………………………………………………………………………………. ……………………………………………………………………………………. ……………………………………………………………………………………. ……………………………………………………………………………………. [1]

7 © Jurong Pioneer Junior College 9729/02/J2 PRELIMINARY EXAM/2025 [Turn Over (iii) Iodoalkanes can be made by warming a bromoalkane with a solution of sodium iodide in dry propanone, in which sodium bromide is almost insoluble. CH3CH2CH2Br + NaI = CH3CH2CH2I + NaBr Suggest why the above reaction produces a high yield of CH 3CH2CH2I despite the C−I bond being weaker than the C−Br bond. For Examiner’s Use ……………………………………………………………………………………. ……………………………………………………………………………………. ……………………………………………………………………………………. ……………………………………………………………………………………. [1] (iv) A student wanted to distinguish 2–bromo–2–methylpropane, (CH3)3CBr, from compound B shown below. The student suggested the following method: Step 1: To 2 cm 3 of each compound, add an equal volume of NaOH(aq). Step 2: Then add 1 cm3 of AgNO3(aq). Step 3: Then add excess of dilute HCl(aq). Identify and explain two improvements to the student’s proposed method. Improvement 1: ……………………………………………………………………………………. ……………………………………………………………………………………. ……………………………………………………………………………………. Improvement 2: ……………………………………………………………………………………. ……………………………………………………………………………………. ……………………………………………………………………………………. [2] [Total: 11]

8 © Jurong Pioneer Junior College 9729/02/J2 PRELIMINARY EXAM/2025 3 Amino acids are the fundamental building blocks of proteins and play crucial roles in various biological processes. Amino acids are crystalline solids with high melting points, are water-soluble, and exist as zwitterions. The general structure of an −amino acid is given below. where R represents the side−chain on the −carbon of amino acid. For Examiner’s Use (a) Explain why amino acids exist as crystalline solids at room temperature. …………………………………………………………………………………………... ……………………………………………………………………………………..……. …………………………………………………………………………………………... [1] (b) The Strecker synthesis is one method to prepare -amino acids in the laboratory by reacting readily available aldehydes or ketones in the presence