2019 ACJC Prelim H2 Chem P3 QP

[Turn over ANGLO-CHINESE JUNIOR COLLEGE DEPARTMENT OF CHEMISTRY Preliminary Examination CHEMISTRY H2 9729/03 Paper 3 Free Response 2 September 2019 2 hours Candidates answer on separate paper. Additional Materials: Cover Page Answer Paper Insert READ THESE INSTRUCTIONS FIRST Write your index number and name, form class and tutorial class 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. Section A Answer all questions. Section B Answer one question. Start each question on a new page of writing paper. Fasten the insert in front of all writing paper at the end of the examination. A Data Booklet is provided. The use of an approved scientific calculator is expected, where appropriate. At the end of the examination, fasten all your work securely together. The number of marks is given in brackets [ ] at the end of each question or part question. This document consists of 14 printed pages. 9729/03/Prelim/19 ANGLO-CHINESE JUNIOR COLLEGE © ACJC 2019 Department of Chemistry

2 © ACJC2019 9729/03/Prelim Exam/2019 [Turn over Section A Answer all the questions from this section. 1 (a) Use of the insert is necessary for this question. Fasten the insert in front of all writing paper at the end of the examination. An iodoalkane, R I, is hydrolysed by aqueous sodium hydroxide. The results obtained from two experiments a re plotted on the insert. In each experiment, the overall [NaOH(aq)] remained virtually constant at the value given beside each graph. (i) Use the graphs on the insert to determine the following. Show all workings clearly. I Use the half -life method to deduce the order of reaction with respect to the iodoalkane. II Use the initial rates method to deduce the order of reaction with respect to sodium hydroxide. III Construct a rate equation for the reaction and use it to calculate a value for the rate constant. Include its units. [7] (ii) Hence draw a fully labelled energy profile diagram of the reaction. [3] (b) Silver(I) iodide and iodine are two solids which have low solubility in water. However when both are mixed together with water and left to stand , they dissolve completely to give a coloured solution of silver(I) triiodide. (i) State the expected colour of the silver(I) triiodide solution. [1] (ii) Write three relevant equilibria equations and use them to explain how the two solids can completely dissolve when mixed with water. [3] (c) Another triiodide compound, nitrogen triiodide, NI3 is a simple covalent molecule that is very sensitive to shock and will decompose rapidly. A touch of a feather or even alpha particles from radioactive decay can trigger an explosion. 2NI3(s) ⟶ N2(g) + 3I2(g) ∆H = –290 kJ mol–1 76.5 kJ mol–1 of energy is needed to convert solid NI3 to gaseous NI3. Use the above information and relevant information from the Data Booklet to calculate the N–I bond energy. [2]

3 © ACJC2019 9729/03/Prelim Exam/2019 [Turn over (d) Alpha particles, He2+ 2 4 are produced from the radio active decay of certain isotopes . An example of one is from the decay of Americium-241. Am95 241 → He2+ 2 4 + M (i) Use the Data Booklet to identify species M that is formed. [1] (ii) Calculate the angle of deflection for M in a uniform electric field if the angle of deflection for He2+ 2 4 is +7.11o. [1] Americium is often used in smoke detectors as the compound AmO 2 and is made from the thermal decomposition of americium(III) ethanedioate, Am2(C2O4)3. Am2(C2O4)3 ⟶ 2AmO2 + 4CO + 2CO2 (iii) Explain why the thermal decomposition is a redox reaction in terms of oxidation state changes. [2] [Total: 20]

4 © ACJC2019 9729/03/Prelim Exam/2019 [Turn over 2 (a) On 12 June 2019, Hong Kong police fired tear gas into the crowds as many took to the streets to protest against a proposed extradition Bill. The active compound in tear gas is 2-chlorobenzalmalononitrile. 2-chlorobenzalmalononitrile 2-chlorobenzalmalononitrile is a solid at room temperature and is dispersed as an aerosol dissolved in a suitable organic solvent, typically dichloromethane, CH2Cl2. Its effects are felt when the solvent evaporates in air and the dry powder touches the eyes, nose and mouth. (i) Suggest, with reasoning, two physical properties that make dichloromethane a suitable solvent. [2] 2-chlorobenzalmalononitrile can be synthesised via the 2 -stage Knoevenagel condensation.

5 © ACJC2019 9729/03/Prelim Exam/2019 [Turn over (ii) State the type of the reaction in stage 2. [1] (iii) Instead of purchasing malononitrile as a starting reagent, it can be made from dichloromethane. Suggest the reagent and conditions needed to convert dichloromethane to malononitrile. [1] The following 3-step mechanism illustrates stage 1.  Malononitrile is deprotonated by a weak base, R 2NH to form its conjugate base, (NC)2CH–.  The conjugate base of malononitrile undergoes nucleophilic addition with 2-chlorobenzaldehyde to give as an intermediate.  The conjugate acid of R2NH is deprotonated by the intermediate. (iv) Describe the 3-step mechanism illustrated above. Show all charges and relevant lone pairs and show the movement of electron pairs by using curly arrows. [3] (v) Suggest another role of the weak base, R2NH. [1] (vi) Compare, and explain, the relative acidities of dichloromethane and malononitrile. [2] (vii) Draw the only two organic products formed when 2-chlorobenzalmalononitrile is heated with acidified potassium manganate(VII). [2]

6 © ACJC2019 9729/03/Prelim Exam/2019 [Turn over (b) During World War II, amphetamine pills were issued to the German army as they promoted alertness and self -confidence while reducing pain, hunger and the need for sleep. Study the two methods of synthesis and answer the questions below. (i) State the reagent used in stage 1 for both methods of synthesis. [1] (ii) One would think that Method 2 would give better yield of amphetamine during synthesis since it only involves one stage as compared to two stages in Method 1, but this is not true. Suggest why the yield of amphetamine via Method 2 would be poor. [1] (iii) Only half of the product formed via Method 1 was biologically active in the body. Account for this observation. [2] (iv) Stage 2 of Method 1 employs the use of platinum metal as a catalyst. State the type of catalysis involved and briefly outline the stages involved in the reaction. [3] (v) Explain why transition metals are useful as catalysts. [1]

7 © ACJC2019 9729/03/Prelim Exam/2019 [Turn over (c) Cisplatin is an anti-cancer drug containing a platinum centre and appears as a light yellow powder. When cisplatin is dissolved in water and allowed to react with the cyclen ligand, the position of equilibrium lies strongly to the right hand side. cisplatin cyclen (i) Define the term ligand. [1] (ii) Suggest signs for the enthalpy change of reaction and entropy change of reaction for the forward reaction , and comment on the spontaneity of the reaction across different temperatures. [2] (iii) Explain why transition metal compounds are coloured. [2] [Total: 25]

8 © ACJC2019 9729/03/Prelim Exam/2019 [Turn over 3 (a) Boeing 787-9 Dreamliners are equipped with electronically dimmable windows. When a constant current is applied, electrochemical reactions happen within a panel and the conversion of col