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