2024 Prelims ACJC H2 Chem P2 (QP)

This paper consists of 22 printed pages and 2 blank pages. Anglo-Chinese Junior College JC2 Preliminary Examination Higher 2 CANDIDATE NAME FORM CLASS TUTORIAL CLASS INDEX NUMBER CHEMISTRY Paper 2 Structured Questions Candidates answer on the Question Paper. Additional materials: Data Booklet 9729/02 21 August 2024 2 hours READ THESE INSTRUCTIONS FIRST Write your form class, index number and name in the spaces provided 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. 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 Question no. Marks 1 / 12 2 / 11 3 / 10 4 / 10 5 / 10 6 / 22 Presentation of answers TOTAL / 75

2 © ACJC2024 9729/Preliminary Examination/2024 [Turn over Section B: Structured Questions (75 marks) Answer all the questions in the spaces provided. 1 Y and Z are two elements found in Period 3. Their fifth to eighth ionisation energies are given in Table 1.1. Table 1.1 successive ionisation energies / kJ mol–1 5th 6th 7th 8th Y 6530 9353 11019 33606 Z 7004 8496 27107 31719 (a) (i) State and explain the group number of Y. ..………………………………………………………………………………..…………. ..………………………………………………………………………………..…………. ..………………………………………………………………………………..…………. ………………………………………………………………………………..………..[1] (ii) Complete the electronic configurations of Y+ and Z+. Y+ 1s2…………………………………………………………………..…………........... Z+ 1s2………………………………………………………………………..………....[1] (iii) From your answer in (a)(ii), explain why the second ionisation energy of Y is expected to be lower than Z. ………………………………………………………………………………..……….….. ..………………………………………………………………………………..…………. ………………………………………………………………………………..……..…[1] (iv) However, it turns out that the second ionisation energies of Y and Z are 2300 kJ mol–1 and 2260 kJ mol–1 respectively. Suggest why Y has a higher second ionisation energy than Z. ..………………………………………………………………………………..…………. ………………………………………………………………………………..……..…[1]

3 © ACJC2024 9729/Preliminary Examination/2024 [Turn over (b) (i) The atomic radii of some Period 4 elements are shown in Fig. 1.1. Fig. 1.1 With reference to Fig. 1.1, describe and explain the shape of the graph from • V to Zn • Ga to Br ..………………………………………………………………………………..…………. ..………………………………………………………………………………..…………. ..………………………………………………………………………………..…………. ..………………………………………………………………………………..…………. ..………………………………………………………………………………..…………. ..………………………………………………………………………………..…………. ..………………………………………………………………………………..…………. ..………………………………………………………………………………..…………. ..………………………………………………………………………………..…………. ………………………………………………………………………………..………..[4] (ii) With reference to the Data Booklet or otherwise, on Fig. 1.1, sketch the ionic radii of the Period 4 elements. You may assume that V to Zn form doubly charged cations. [2]

4 © ACJC2024 9729/Preliminary Examination/2024 [Turn over (c) Draw and label the d orbitals in cobalt ion. [2] [Total: 12]

5 © ACJC2024 9729/Preliminary Examination/2024 [Turn over BLANK PAGE

6 © ACJC2024 9729/Preliminary Examination/2024 [Turn over 2 The hydroboration-oxidation reaction of an alkene bond using borane, BH3, provides a useful method for hydration. Using this reaction, 1 -methylcyclohexene can be converted to trans-2-methylcyclohexanol as shown in Fig. 2.1. Fig. 2.1 (a) (i) Explain the role of borane in Fig. 2.1. ..………………………………………………………………………………..…………. ..………………………………………………………………………………..…………. ………………………………………………………………………………..……..…[1] (ii) Suggest why the trans configuration is favoured in the product formed in Fig. 2.1. ..………………………………………………………………………………..…………. ..………………………………………………………………………………..…………. ………………………………………………………………………………..………..[1] (b) Suggest a chemical test that would allow you to distinguish between 2-methylcyclohexanol and ethanol. Include a relevant equation in your answer. ………………………………………………………………………………..……….………..... ………………………………………………………………………………..……….………..... ..………………………………………………………………………………..………….……... ………………………………………………………………………………..………………..[2] 1-methylcyclohexene borane trans-2-methylcyclohexanol

7 © ACJC2024 9729/Preliminary Examination/2024 [Turn over (c) Borane dimerises to form the more stable diborane, B2H6, shown in Fig. 2.2. (i) Suggest two unusual features about the bonding shown in Fig. 2.2. ..………………………………………………………………………………..…………. ..………………………………………………………………………………..…………. ..………………………………………………………………………………..…………. ………………………………………………………………………………..……..…[2] (ii) Fig. 2.3 depicts another equivalent representation of the bonding in diborane. The bridging B-H-B bonds are curved, giving them the name ‘banana bonds’. The ‘banana bonds’ consist of three-centre-two-electron bonds, which are electron-deficient chemical bonds where three atoms share two electrons. State the total number of bonding electrons in diborane. ……………………………………………………………………..……..……………[1] (iii) The B–H bonds in diborane have different bond lengths. The terminal B–H bonds are 0.119 nm in length. Explain how the bond length of the bridging B –H bonds compares with the terminal B–H bonds. Note: Fig. 2.3 is not drawn to scale. ..…………………………………………………..………………………..………….…. ..……………………………………………………………………………..………….… ………………………………………………..…………………………..…………...[1] Fig. 2.2 Fig. 2.3 0.119 nm

8 © ACJC2024 9729/Preliminary Examination/2024 [Turn over (d) 1-methylcyclohexene can react with iodine monochloride, ICl. Name and d escribe the mechanism of this reaction, showing curly arrows, charges, dipoles and any relevant lone pairs. [3] [Total: 11]

9 © ACJC2024 9729/Preliminary Examination/2024 [Turn over 3 Cyanogen chloride, ClCN, exists as a highly toxic gas and reacts rapidly with hydroxide ions. equation 1 ClCN + OH– → HOCN + Cl– (a) (i) State the hybridisation of the carbon atom in cyanogen chloride. ………………..…………………………………………………………..……………[1] (ii) Name the type of reaction occurring in equation 1. ……………..……………………………………………………………..……………[1] (b) (i) 0.06 g of cyanogen chloride was fully dissolved in 100 cm3 of 2 mol dm–3 aqueous sodium hydroxide. The rate constant, k, for the reaction is 4.2 mol–1 dm3 s–1. Construct the rate equation for equation 1. …………..………………………………………………………………..……………[1] (ii) Calculate the concentration of cyanogen chloride in the solution. [1] (iii) Using your answer in (b)(ii) and the information in (b)(i), deduce the half -life of the reaction. [1]

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