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. …………………………………………………………………………………………. …………………………………………………………………………………………. …………………………………………………………………………………………. …………………………………………………………………………………………. ……………………………………………………………………………………… [3] (c) Orange street-lamps contain sodium with a small amount of neon. Light is produced when the gaseous atoms are ionised in an electric field. Ne(g) → Ne+(g) + e− 1st I.E = +2080 kJ mol−1 Na(g) → Na+(g) + e− 1st I.E = +494 kJ mol−1 (i) Explain the difference in the first ionisation energies of neon and sodium. …………………………………………………………………………………………. …………………………………………………………………………………………. …………………………………………………………………………………………. …………………………………………………………………………………………. …………………………………………………………………………………………. ……………………………………………………………………………………… [2] (ii) When the lamps are switched on, they first emit a red glow characteristic of neon, but after some time, the orange glow of sodium predominates. Suggest why neon is ionised first even though its first ionisation energy is much higher than that of sodium.

4 © DHS 2023 9729/02 …………………………………………………………………………………………. ……………………………………………………………………………………… [1] [Total: 10] 2 Compound M has molecular formula, C6H8O2. M reacts with an excess of hot concentrated KMnO 4 to produce two different organic molecules L and K. (a) K has molecular formula C2H2O4 and is further oxidised to form CO2. (i) Name K. ……………………………………………………………………………………… [1] (ii) Write an equation for the oxidation of K to form CO 2, using [O] to represent the oxidising agent. ……………………………………………………………………………………… [1] (b) L has molecular formula C4H6O3. When pure samples of L are separately added to two different reagents, the observations in Table 2.1 are recorded. Table 2.1 test reagent observation 1 alkaline aqueous iodine pale yellow precipitate 2 phosphorus(V) chloride misty acid fumes (i) Name the type of reaction occurring to L in test 1. ……………………………………………………………………………………… [1] (ii) Based on the observation for test 2, name two functional groups that could be present in L. ……………………………………………………………………………………… [1] (iii) Deduce the structure of L. [1]

5 © DHS 2023 9729/02 [Turn over (c) Suggest a possible structure of M, C6H8O2, showing the skeletal formula. [2] Fig. 2.1 shows a reaction scheme of compound N. R MnO4 / H+, heat step 2 + CO2S (C8H6O4) N C2H3O C2H3O CH3 step 1 Fig. 2.1 (d) (i) N reacts with 2,4-dinitrophenylhydrazine to give an orange precipitate. Explain this observation. …………………………………………………………………………………………. ……………………………………………………………………………………… [1] (ii) R is the major product of the reaction occurring in step 1. Use this information and your answer in (d)(i) to deduce the structure of N. Explain your answer. …………………………………………………………………………………………. …………………………………………………………………………………………. …………………………………………………………………………………………. ……………………………………………………………………………………… [2] (iii) State the reagents and conditions required for step 1. ……………………………………………………………………………………… [1] (iv) Suggest the structure of compound S.

6 © DHS 2023 9729/02 [1] [Total: 12] 3 (a) A series of kinetics experiments was carried out at a constant temperature to study the mechanism of ester hydrolysis under basic conditions. The overall chemical reaction is described below. OCH3 O CH3 + OH + CH3OH OCH3 O The initial rates of reaction with v arying ester concentrations were measured at [OH–] = 0.90 mol dm–3 and [OH–] = 1.50 mol dm–3. Fig. 3.1 shows the graph of the results obtained. 0.00 0.02 0.04 0.06 0.08 0.10 0.12 0.14 0.00 0.10 0.20 0.30 0.40 0.50 0.60 0.70 initial rate / mol dm–3 min–1 [ester] / mol dm–3 [OH–] = 0.90 mol dm–3 [OH–] = 1.50 mol dm–3

7 © DHS 2023 9729/02 [Turn over Fig. 3.1 (i) By quoting relevant data from Fig. 3.1, determine the order of reaction with respect to each reactant. Show your reasoning clearly. …………………………………………………………………………………………. …………………………………………………………………………………………. …………………………………………………………………………………………. …………………………………………………………………………………………. …………………………………………………………………………………………. …………………………………………………………………………………………. …………………………………………………………………………………………. ……………………………………………………………………………………… [2] (ii) Using your answer in (a)(i), write the rate equation for the reaction. ……………………………………………………………………………………… [1] (iii) Using your answer in (a)(ii) and relevant data from Fig. 3.1, calculate the value of the rate constant under the experiment conditions. State its units. [1]

8 © DHS 2023 9729/02 (b) The proposed mechanism for the hydrolysis reaction is shown in Fig. 3.2. OCH3 O CH3 + OH OCH3 O H + CH3O OCH3 O H + + CH3OH slow step 1: step 2: step 3: OCH3 CH3 O OH OCH3 CH3 O OH CH3O OCH3 O Fi