HCI 2021 Prelim Paper 3 Questions

This document consists of 27 printed pages and 1 blank page. HWA CHONG INSTITUTION C2 Preliminary Examinations Higher 2 CANDIDATE NAME CT GROUP 20S CENTRE NUMBER INDEX NUMBER CHEMISTRY Paper 3 Free Response Candidates answer on the Question Paper. Additional Materials: Data Booklet 9729/03 16 September 2021 2 hours READ THESE INSTRUCTIONS FIRST Write your Centre number, index number, name and CT group in the spaces 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. If additional space is required, you should use the pages at the end of this booklet. The question number must be clearly shown. Section A Answer all questions. Section B Answer one question. 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. No. of sheets of writing paper submitted (write 0 if none) For Examiner’s Use 1 / 21 2 / 18 3 / 21 Circle your option below 4 / 5 / 20 Deductions Total / 80

2 © Hwa Chong Institution 2021 9729/03/C2Prelim 2021 [Turn over Section A Answer all the questions in this section. 1 (a) With the aid of the Boltzmann distribution, explain how an increase in temperature will affect the rate constant of a reaction. [3] For Examiner's use ……………………………………………………….……………………………………………… ……………………………………………………….……………………………………………… ……………………………………………………….……………………………………………… ……………………………………………………….……………………………………………… ……………………………………………………….……………………………………………… ……………………………………………………….……………………………………………… ……………………………………………………….……………………………………………… ……………………………………………………….……………………………………………… ……………………………………………………….……………………………………………… ……………………………………………………….……………………………………………… ……………………………………………………….……………………………………………… ……………………………………………………….……………………………………………… ……………………………………………………….……………………………………………… ……………………………………………………….……………………………………………… ……………………………………………………….……………………………………………… ……………………………………………………….……………………………………………… (b) Bromoalkanes can react with sodium cyanide to form nitriles. Depending on the structure of the bromoalkane, the reaction can proceed via the SN1 or SN2 mechanism. Reaction 1 follows the SN1 mechanism under certain conditions. reaction 1 (i) Describe the mechanism for reaction 1. In your answer, show all relevant charges, lone pairs, dipoles and show the movement of electron pairs by using curly arrows. [2] (ii) Hence, write the rate equation for reaction 1. [1] (iii) What is meant by the term order of reaction? [1]

3 © Hwa Chong Institution 2021 9729/03/C2Prelim 2021 [Turn over (iv) An experiment is carried out to study the kinetics of reaction 1. The concentration of the bromoalkane is monitored at timed intervals, with sodium cyanide present in large excess. Sketch a suitable graph and show clearly on the graph how the results of the experiment can be used to confirm the reaction is first order with respect to the concentration of the bromoalkane. [2] For Examiner's use (v) The reaction below follows the same mechanism as reaction 1. reaction 2 Predict the relative rates of reaction 1 and reaction 2 under identical conditions, giving your reasoning. [1] ……………………………………………………….………………………………………… ……………………………………………………….………………………………………… ……………………………………………………….………………………………………… ……………………………………………………….………………………………………… ……………………………………………………….………………………………………… ……………………………………………………….………………………………………… ……………………………………………………….………………………………………… ……………………………………………………….………………………………………… ……………………………………………………….………………………………………… ……………………………………………………….………………………………………… ……………………………………………………….………………………………………… ……………………………………………………….………………………………………… ……………………………………………………….………………………………………… ……………………………………………………….………………………………………… ……………………………………………………….………………………………………… ……………………………………………………….………………………………………… ……………………………………………………….………………………………………… ……………………………………………………….………………………………………… ……………………………………………………….………………………………………… ……………………………………………………….…………………………………………

4 © Hwa Chong Institution 2021 9729/03/C2Prelim 2021 [Turn over ……………………………………………………….………………………………………… ……………………………………………………….………………………………………… ……………………………………………………….………………………………………… ……………………………………………………….………………………………………… ……………………………………………………….………………………………………… ……………………………………………………….………………………………………… ……………………………………………………….………………………………………… ……………………………………………………….………………………………………… ……………………………………………………….………………………………………… ……………………………………………………….………………………………………… ……………………………………………………….………………………………………… ……………………………………………………….………………………………………… ……………………………………………………….………………………………………… ……………………………………………………….………………………………………… ……………………………………………………….………………………………………… ……………………………………………………….………………………………………… ……………………………………………………….………………………………………… ……………………………………………………….………………………………………… ……………………………………………………….………………………………………… ……………………………………………………….………………………………………… ……………………………………………………….………………………………………… ……………………………………………………….………………………………………… ……………………………………………………….………………………………………… ……………………………………………………….………………………………………… ……………………………………………………….………………………………………… ……………………………………………………….………………………………………… ……………………………………………………….………………………………………… …………………………………………………………………………………………………. For Examiner's use

5 © Hwa Chong Institution 2021 9729/03/C2Prelim 2021 [Turn over (c) When another bromoalkane, P, reacts with aqueous sodium hydroxide, the reaction could occur via both SN1 and SN2 mechanisms. Two products, Q and R, are obtained. For Examiner's use (i) Name compound P. [1] (ii) Explain why compound P can react via the SN1 mechanism, even though it is a primary bromoalkane. Hence suggest how product R may be formed in the reaction. Use the concept of delocalisation in your answer. [2] (iii) State the type of stereoisomerism shown by product R and draw its stereoisomers. [2] (iv) Compound P can react with ethylamine to form compound S, C6H13N. Draw the displayed formula of compound S. [1] ……………………………………………………….………………………………………… ……………………………………………………….………………………………………… ……………………………………………………….………………………………………… ……………………………………………………….………………………………………… ……………………………………………………….………………………………………… ……………………………………………………….………………………………………… ……………………………………………………….………………………………………… ……………………………………………………….………………………………………… ……………………………………………………….………………………………………… ……………………………………………………….………………………………………… ……………………………………………………….………………………………………… ……………………………………………………….………………………………………… ……………………………………………………….………………………………………… ……………………………………………………….………………………………………… ……………………………………………………….………………………………………… ………………………………………………………………………………………………….

6 © Hwa Chong Institution 2021 9729/03/C2Prelim 2021 [Turn over ……………………………………………………….………………………………………… ……………………………………………………….………………………………………… ……………………………………………………….………………………………………… ……………………………………………………….………………………………………… ……………………………………………………….………………………………………… ……………………………………………………….………………………………………… ……………………………………………………….………………………………………… ……………………………………………………….………………………………………… ………………………………………………………….………………………………………