RI 2018 Prelim P2 QP

© Raffles Institution 2018 9729/02/S/18 [Turn Over RAFFLES INSTITUTION 2018 YEAR 6 PRELIMINARY EXAMINATION Higher 2 CANDIDATE NAME CLASS INDEX NUMBER CHEMISTRY 9729/02 Paper 2 Structured Questions 11 September 2018 2 hours Candidates answer on the Question Paper. Additional Materials: Data Booklet READ THESE INSTRUCTIONS FIRST Do not open this question booklet until you are told to do so. Write your name, class and index number in the spaces provided at the top of this page. Write in dark blue or black pen in the spaces provided. You may use a soft pencil for any diagrams, graphs or rough working. Do not use staples, paper clips, highlighters, glue or correction fluid. Answer all questions. A Data Booklet is provided. Do not write anything in it. You are reminded of the need for good English and clear presentation in your answers. The number of marks is given in brackets [ ] at the end of each question or part question. For Examiner’s Use 1 / 8 2 / 13 3 / 16 4 / 13 5 / 10 6 / 15 Total / 75 This document consists of 23 printed pages.

For examiner’s use 2 © Raffles Institution 2018 9729/02/S/18 [Turn Over Answer all the questions in the spaces provided. 1 Gemstones such as amethysts, pearls and malachites contain compounds of main group and transition elements. Fig. 1.1 shows the logarithm of the ionisation energies, log (IE), for the outermost ten electrons in an atom of an element X, which has atomic number smaller than 20. number of electrons removed Fig. 1.1 (a) Deduce which G roup in the Periodic Table X belongs to and state the identity of X. Explain your answer. ………………………………………………….………..………………………………………... ……………………………………………….……………………………………………….....… ……………………………………………….………………………………………………….… ………………………………………………..………………………….…………….…….…[3] (b) The colour of amethyst is caused by the presence of compounds containing manganese and iron. Explain why the first ionisation energies of manganese and iron are similar. ……………………………………….……………………………………………….……....…… ……………………………………….…………………………………………………….....…… ……………………………………….…………………………………………………….....…… ………………………………………………….…………………………………………..……... ……………………………………………….………………………………………..………...… ………………………………………………..………………………….…………….…….…[3] 1 2 3 4 5 6 7 8 9 10 11 log (IE)

For examiner’s use © Raffles Institution 2018 9729/02/S/18 [Turn Over 3 (c) Use of the Data Booklet is relevant to this question. Malachites contain copper(II) carbonate while pearls contain calcium carbonate. Predict whether calcium carbonate or copper( II) carbonate has a higher decomposition temperature. Explain your answer. …………………………………………………………………………………………….………. …………………………………………………………………………………………….….…… …………………………………………………………………………………………….………. …………………………………………………………………………………………….….…… …………………………………………………………………………………………….………. …………………….……………………………………………….…………………….….… [2] [Total: 8]

For examiner’s use © Raffles Institution 2018 9729/02/S/18 [Turn Over 4 2 (a) Polycyclic aromatic hydrocarbons (PAHs) are potential carcinogens. Anthracene is an example of a PAH and its Kekulé structure is shown in Fig. 2.1. Fig. 2.1 (i) A compound is aromatic if it satisfies the following criteria: • it is a cyclic planar molecule, • it has a delocalised  electron system, and • it has (4n + 2)  electrons, where n is an integer. By considering the hybridisation of the carbon atoms in anthracene and the criteria for aromaticity, explain why anthracene is aromatic. ……………………………………………………………………………………..……… ……………………………………………………………………………………..……… …………………………………………………………………………………..………… ……………………………………………………………………………………..……… ……………………………………………………………………………………..……… …………………………………………………………………………………..………… …………………………………………………………………….……….….……..…[3] (ii) The enthalpy change of hydrogenation of cyclohexene to cyclohexane is −118 kJ mol−1. Using the K ekulé structure given in Fig. 2.1, calculate the enthalpy change of complete hydrogenation of anthracene, ∆H1. [1]

For examiner’s use © Raffles Institution 2018 9729/02/S/18 [Turn Over 5 (iii) Fig. 2.2 is the actual representation of anthracene. Fig. 2.2 Complete the energy level diagram below using the data in Table 2.1. Hence, calculate the actual value for the enthalpy change of complete hydrogenation of anthracene, ∆H2. Table 2.1 compound formula enthalpy change of formation / kJ mol−1 anthracene C14H10(s) +129 tetradodecahydroanthracene C14H24(s) −356 ∆H2 = ……………………………….. [3] (iv) Using your answers to (a)(ii) and (a)(iii), calculate the resonance energy of anthracene. [1] 0 energy / kJ mol−1

For examiner’s use © Raffles Institution 2018 9729/02/S/18 [Turn Over 6 (b) Table 2.2 shows some information on anthracene and other PAHs found in smoked fish. Table 2.2 PAH structure mean concentration (Cm) / ppm Toxicity Equivalency Factor (TEF) anthracene C14H10 0.029 0.01 chrysene C18H12 0.135 0.01 benzo[a]pyrene C20H12 0.204 1.00 (i) The carcinogenic toxic equivalent (TEQ) of PAHs in smoked fish can be calculated using equation 2.1. TEQ = Sum of [Cm (in ppm)  TEF] ------ equation 2.1 Using equation 2.1 and the data from Table 2.2, calculate the TEQ of smoked fish. [1]

For examiner’s use © Raffles Institution 2018 9729/02/S/18 [Turn Over 7 (ii) For an average person, the excess cancer risk (ECR) resulting from exposure to PAHs through smoked fish consumption can be determined using equation 2.2. ECR = TEQ body weight in kg  1.37  10−3 ------ equation 2.2 Given that the acceptable ECR value set by United States Environmental Protection Agency is 1.0  10−6, use equation 2.2 to determine the ECR value due to the consumption of smoked fish by a 70 kg person. Hence, state whether the person is at risk of cancer. [1]

For examiner’s use © Raffles Institution 2018 9729/02/S/18 [Turn Over 8 (c) Phenolphthalein is formed when phenol undergoes electrophilic substitution with phthalic anhydride. The overall equation for the reaction is shown below. (i) As phenolphthalein is a carcinogen, it has been replaced by thymolphthalein , which can be formed by a similar reaction between thymol and phthalic anhydride. By using the structure of thymol as shown below, draw the structure of thymolphthalein. thymol [1] (ii) Explain whether thymol or phenol undergoes electrophilic substitution more readily. ……………………………………………………………………….…………...……….. ……………………………………………………………………….…………...……….. …………………………………………………………………….……………...……….. ……………………………………………………………………….………….………[1]

For examiner’s use © Raffles Institution 2018 9729/02/S/18 [Turn Over 9 (d) Phenolphthalein indicator is colourless . Under basic condition s, phenolphthalein undergoes dissociation to form its conjugate base, which is pink in colour. The conjugate base of phenolphthalein is found to be A and not B. A B Explain why the structure of A is more stable than that of B. ……………………………………………………………………………...…………………….. …………………………………………………………………………….……………………… ……………………………………………………………………………...…………………….. ………………………………………………………………………………………………….[1] [Total: 13]

For examiner’s use © Raffles Institution 2018 9729/02/S/18 [Turn Over 10 3 (a) Acid derivatives, RCOY, are compounds formed when the –OH group of carboxylic acid is replaced by a different group (Y). They have the general structure as shown below. Acid derivatives und