2025 ASRJC Prelim H2Chem P2 QP

ASRJC JC2 PRELIM 9729/02/H2 [Turn over ANDERSON SERANGOON JUNIOR COLLEGE 2025 JC 2 PRELIMINARY EXAMINATION NAME:______________________________ ( ) CLASS: 25 / _____ CHEMISTRY 9729/02 Paper 2 Structured Questions 27 August 2025 2 hours Candidates answer on the Question Paper. Additional Materials: Data Booklet READ THESE INSTRUCTIONS FIRST Write your name, class and register number 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. 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 Paper 2 1 /8 2 /16 3 /25 4 /14 5 /12 Total / 75 This document consists of 22 printed pages and 2 blank pages.

2 ASRJC JC2 PRELIM 9729/02/H2 Answer all the questions. 1 (a) Mild steel is an alloy that contains iron and carbon. A sample of mild steel was analysed, and four different types of atoms were identified; A, B, C and D. Table 1.1 shows information about the four types of atoms found in the sample. Table 1.1 atom relative mass relative % abundance A 12.00 0.238 B 13.00 0.012 C 53.94 5.79 D 55.93 93.96 (i) Calculate the relative atomic mass of carbon in this sample to four significant figures. Show your working. [1] (ii) In an experimental set -up, beams of particles travelling at the same speed from different sources are subjected to an electric field as shown in Fig. 1.1. A beam of protons with an angle of deflection of 60° has already been drawn. + protons Fig. 1.1 Under identical conditions, beams of particles 12C2+ and 56Fe2+ were subjected to the same electric field. Calculate the angle of deflection of 12C2+ and 56Fe2+particles under the electric field and sketch the beams of 12C2+ and 56Fe2+ on Fig. 1.1. Label the beams clearly. [2]

3 ASRJC JC2 PRELIM 9729/02/H2 [Turn over (b) The compound C6H6 has many possible structural isomers. Three suggested structures of C6H6 are shown in Fig. 1.2. Kekulé benzene Dewar benzene Ladenburg benzene Fig. 1.2 (i) Using Fig. 1.2, complete Table 1.2 to predict the number of carbon atoms that have sp, sp 2 and sp 3 hybridisation in Kekulé benzene, Dewar benzene and Ladenburg benzene. Table 1.2 C6H6 structure sp hybridised sp2 hybridised sp3 hybridised Kekulé benzene Dewar benzene Ladenburg benzene [2]

4 ASRJC JC2 PRELIM 9729/02/H2 (ii) Dewar benzene contains both  bonds and  bonds. By reference to the hybridrisation of the carbon atoms and orbital overlap, describe the covalent bonding in Dewar benzene. …………………………………………………………………………………………………. …………………………………………………………………………………………………. …………………………………………………………………………………………………. …………………………………………………………………………………………………. …………………………………………………………………………………………………. …………………………………………………………………………………………………. …………………………………………………………………………………………………. …………………………………………………………………………………………………. …………………………………………………………………………………………………. ……………………………………………………………………………………………… [2] (iii) Suggest why Dewar benzene and Ladenburg benzene are unstable isomers of C6H6. ………………………………………………………………………………………………….. ……………………………………………………………………………………………… [1] [Total: 8]

5 ASRJC JC2 PRELIM 9729/02/H2 [Turn over 2 Aluminum is the most abundant metal in the earth’s crust and has been produced commercially since 1888. It is now the second most used metal in the world after iron. Approximately 75% of aluminum ever produced is still in use today, as it can be recycled endlessly without compromising any of its unique properties or quality. (a) Aluminum objects that have had the aluminum oxide layer removed may be anodised. (i) Complete Table 2.1 to show the relevant half-equations, during the anodisation of an aluminum object. Table 2.1 half-equation anode .…. Al + .….. H2O → ….. Al2O3 + ….. H+ + …...e cathode [2] (ii) During the anodis ation of an aluminum object, 3.50 g of a protective layer aluminum oxide is formed in 2 hours. Calculate the value of the current used. [2]

6 ASRJC JC2 PRELIM 9729/02/H2 (b) Fig. 2.1 shows an incomplete energy cycle involving aluminium oxide, Al2O3. Fig. 2.1 (i) Complete line C. Include state symbols. [1] line A: 2Al(s) + O2(g) line D: Al2O3(s) line B: 2Al(g) + 3O(g) line C: ………………………….................. process 1: enthalpy change of formation of Al2O3(s) process 2: enthalpy change of atomisation of Al and O process 3 process 4: lattice energy of Al2O3(s)

7 ASRJC JC2 PRELIM 9729/02/H2 [Turn over (ii) Using Fig 2.1, the data in Table 2.2, together with data from the Data Booklet, to calculate the lattice energy of Al2O3(s). Table 2.2 Ho / kJ mol–1 1st electron affinity of oxygen, O(g) + e– → O–(g) –141 2nd electron affinity of oxygen, O–(g) + e– → O2–(g) +790 standard enthalpy change of atomisation of Al(s) +326 standard enthalpy change of formation of Al2O3(s) –1676 [2] (iii) Explain why the first electron affinity of oxygen is exothermic, but the second electron affinity is endothermic. ………………………………………………………………………………………………… ………………………………………………………………………………………………… ………………………………………………………………………………………………… ………………………………………………………………………………………………… ………………………………………………………………………………………………… …………………………………………………………………………………………….. [2]

8 ASRJC JC2 PRELIM 9729/02/H2 (c) When aluminum reacts with dry chlorine, aluminum chloride, AlCl3, is formed. (i) AlCl3 can undergo dimerisation to form Al2Cl6. With the aid of a diagram, name the type of bond form ed during dimerisation and explain why this bond is formed. ………………………………………………………………………………………………… …………………………………………………………………………………………….. [2] (ii) When AlCl3 is dissolved in water, a solution of pH 3.0 is formed. Explain with the aid of a balanced equation why the solution has a pH of 3.0. ………………………………………………………………………………………………… ………………………………………………………………………………………………… ………………………………………………………………………………………………… …………………………………………………………………………………………….. [2] (iii) AlCl3 can be used as a catalyst in the reaction of methylbenzene with chloroethane to form 4-ethylmethylbenzene. Describe the mechanism of this reaction. [3] [Total: 16]

9 ASRJC JC2 PRELIM 9729/02/H2 [Turn over