2023_DHS_H2_Chem_Prelim_Paper_2_QP

© DHS 2023 9729/02 [Turn over Name: Centre/Index Number: Class: DUNMAN HIGH SCHOOL Preliminary Examination Year 6 H2 CHEMISTRY Paper 2 Structured Questions Candidates answer on the Question Paper. Additional Materials: Data Booklet 9729/02 14 September 2023 2 hours READ THESE INSTRUCTIONS FIRST Write your centre number, index number, name and class 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. You may lose marks if you do not show your working or if you do not use appropriate units. 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 10 2 12 3 14 4 14 5 25 Total 75 This document consists of 25 printed pages and 1 blank page. This document consists of 20 printed pages.

2 © DHS 2023 9729/02 Answer all the questions in the spaces provided. 1 (a) A fluorophore is a fluorescent chemical compound that can re -emit light upon light excitation. Fluorophores typically contain several combined aromatic groups, or planar or cyclic molecules with several π bonds. Derivatives of trans -stilbene ha ve been recently studied due to their well -known fluorophore properties and they are generally more stable than cis -stilbene. The structure of cis-stilbene is shown in Fig. 1.1. Fig. 1.1 (i) Explain why the melting point of trans -stilbene is higher than that of cis-stilbene. …………………………………………………………………………………………. …………………………………………………………………………………………. …………………………………………………………………………………………. ……………………………………………………………………………………… [1] (ii) Based on the structure of stilbene, suggest a reason why trans -stilbene is more stable than cis-stilbene. …………………………………………………………………………………………. …………………………………………………………………………………………. …………………………………………………………………………………………. ……………………………………………………………………………………… [1] (b) Aluminium chloride, A lCl3, is used as a halogen carrier in order for chlorination of benzene to take place in stilbene. AlCl3 + Cl2 ⇌ AlCl4 – + Cl + (i) Name the type of bond formed when AlCl3 reacts with C l2. Explain how this bond is formed. …………………………………………………………………………………………. …………………………………………………………………………………………. …………………………………………………………………………………………. ………………………………………………………………………………………….

3 © DHS 2023 9729/02 [Turn over ……………………………………………………………………………………… [2] (ii) Draw the dot-and-cross diagram for the AlCl4 – ion. Use the VSEPR theory to state and explain the shape of the ion and the bond angle present. …………………………………………………………………………………………. ………………………………………………………………………………………