NYJC Prelim H2 Chem 9729 P3

[Turn Over NANYANG JUNIOR COLLEGE JC 2 PRELIMINARY EXAMINATION Higher 2 CANDIDATE NAME CLASS TUTOR’S NAME CHEMISTRY 9729/03 Paper 3 Free Response September 2025 2 hours Candidates answer on the Question Paper. Additional Materials: Data Booklet READ THESE INSTRUCTIONS FIRST Write your name and class on all the work you hand in. 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. For Examiner’s Use 1 / 22 2 / 20 3 / 18 4 / 20 5 / 20 Total / 80 This document consists of 28 printed pages. H

2 H2 Chemistry 9729/03 NYJC J2/2025 Prelim Section A Answer all the questions in this section. 1 (a) The pH values of the solutions of four chlorides are given in Table 1.1. Table 1.1 compound pH of 1.0 mol dm−3 solution BeCl2 x NaCl 7.0 AlCl3 3.0 PCl5 1.0 (i) Explain the difference in pH values of solutions of NaCl, AlCl3 and PCl5, in terms of the structures of the chlorides. Include appropriate equation(s) in your answer. [4] (ii) Using the Data Booklet, suggest how the pH value of 1.0 mol dm −3 solution of BeCl2 compares to 1.0 mol dm−3 solution of AlCl3. Explain your answer. [2] (iii) At certain temperatures, aluminum chloride exists as A l2Cl6 molecules. Draw the structure of Al2Cl6. Label the co-ordinate bonds on your structure. [1]

3 H2 Chemistry 9729/03 NYJC J2/2025 Prelim [Turn Over (b) Beryllium, in Period 2, is the only element in Group 2 that shares very similar chemical properties with aluminium which is in Period 3. Describe the similarities in their acid-base behaviour and explain why beryllium oxide reacts similarly like aluminium oxide. Illustrate the reactions of beryllium oxide with equations. [2]

4 H2 Chemistry 9729/03 NYJC J2/2025 Prelim (c) BrCl reacts with benzene in the presence of AlCl3 in an electrophilic substitution reaction to produce bromobenzene. (i) Explain why bromobenzene is made in preference to chlorobenzene during the reaction. [1] (ii) Hence, draw the electrophilic substitution mechanism of the reaction. [2] (iii) The position of substitution in the electrophilic substitution of mono -substituted arene depends on the nature of the group, Z, already attached to the ring. This selectivity can be explained based on the stability of the intermediate formed in the first step. Fig. 1.1 shows three possible first steps in the mono-bromination of a mono-substituted arene and the products obtained. Z Z Br H + + Z H Br Z Br H + Z Br Z Br Z Br Fig. 1.1 isomer 2-position isomer 3-position isomer 4-position 2-position 3-position 4-position Use this information to predict which substituted isomers in Fig. 1.1 will be formed the least and the most when Z is a −C(CH3)3 group. Explain your reasoning. [2] (iv) When Z is a −NH2 group and was reacted with concentrated HNO 3 and concentrated H2SO4, the proportion of 3-nitrophenylamine was found to be unexpectedly high. Explain why 3-nitrophenylamine was the major product. [1]

5 H2 Chemistry 9729/03 NYJC J2/2025 Prelim [Turn Over

6 H2 Chemistry 9729/03 NYJC J2/2025 Prelim (d) Three organohalogeno compounds are shown. C6H5CH2Cl C6H5Cl C6H5COCl A B C Arrange A, B and C in order of increasing relative rate of hydrolysis. Explain your answer. [3]

7 H2 Chemistry 9729/03 NYJC J2/2025 Prelim [Turn Over (e) The different reactivities of organic halogeno compounds, and of amines and alcohols, can be exploited in successive reactions of dihalogeno compounds. Suggest the structures of the intermediates D and F and the products E and G. E and G are cyclic compounds. (i) CH3 I Cl OH−(aq) (1 mol) D NH3 in ethanol E [2] (ii) ClCH2COCl F G NH2CH2CH2OH add Na and warm C4H7NO2 [2] [Total: 22]

8 H2 Chemistry 9729/03 NYJC J2/2025 Prelim 2 (a) A calorimeter containing 300 cm3 of water at 25 °C was calibrated. 10 kJ of heat energy from a heating coil was used to increase the temperature of water by 7.5 °C. Calculate the heat capacity of the empty calorimeter. [2] (b) Ag2CO3 is a sparingly soluble salt. A 100 cm3 saturated solution of Ag2CO3 in water was found to contain 2.57 × 10−4 mol dm–3 of Ag+ ions. (i) Calculate the Ksp of Ag2CO3 and state its units. [2] (ii) Hence, calculate the solubility of Ag2CO3 when 2.50 g of Na2CO3 solid was added to the solution above. [2]

9 H2 Chemistry 9729/03 NYJC J2/2025 Prelim [Turn Over (c) The term ‘tri -iodide’ refers to molecules that contain three iodine atoms in their molecular formula, such as nitrogen tri-iodide, NI3, and aluminium tri-iodide, AlI3. AlI3 has a simple molecular structure. In the gas phase, it dimerises readily to form the dimer Al2I6. The two species are related by the equilibrium shown below. Al2I6(g) ⇌ 2AlI3(g) ∆H > 0 (i) A 10.0 g sample of Al2I6 was allowed to vapourise in a 2 dm3 vessel at 400 oC. Calculate the initial pressure of Al2I6. [1] (ii) Given that the degree of dissociation of Al2I6 was 0.35, calculate the value of Kp for the equilibrium at 400 oC. State its units. [3] (iii) Explain the effect on the degree of dissociation of Al2I6 if the reaction was carried out at 300 oC. [2]

10 H2 Chemistry 9729/03 NYJC J2/2025 Prelim (d) Alcohols are very useful in organic synthesis and can be used to produce a wide variety of compounds. The structural formula of one such alcohol is shown below. compound A (C13H20O2) (i) When compound A is heated with an excess of concentrated sulfuric acid, a mixture of two isomeric hydrocarbons, P and Q are produced. Draw the structures of P and Q. [2] Compound D can be formed from compound A via a five-step synthesis as shown in Fig. 2.1. Fig. 2.1 (ii) Suggest the type of reaction in step 1. [1] (iii) State the reagents and conditions required for steps 2 to 4 and draw the structures of B and C. [5]