2020 YIJC Prelim Exam Paper 3 QP

©YIJC [Turn over YISHUN INNOVA JUNIOR COLLEGE JC 2 PRELIMINARY EXAMINATION Higher 2 CANDIDATE NAME CG INDEX NO CHEMISTRY Paper 3 Free Response Candidates answer on the Question Paper. Additional Materials: Data Booklet 9729/03 16 September 2020 2 hours READ THESE INSTRUCTIONS FIRST This document consists of 26 printed pages and 6 blank pages. For Examiner’s Use Section A 1 /20 2 /16 3 /24 Section B 4 /20 5 /20 Penalty /80 Write your name, class and index number on all the work you hand in. Write in dark blue or black pen on both sides of the paper. 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 the questions. Section B Answer one question. The use of an approved scientific calculator is expected, where appropriate. A Data Booklet is provided. 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.

2 ©YIJC [Turn over Section A Answer all the questions in this section. 1 Chlorine is an element in Group 17 of the Periodic Table. It exists as a diatomic gas at room temperature. Chlorine can also be found in many inorganic and organic compounds. (a) Predict the colour of the final solutions when  Cl2(aq) is added to KBr(aq)  I2(aq) is added to KCl(aq) Write equations for any reactions that occur. State clearly if no reaction occurs. [2] (b) Describe and explain the trend in the thermal stabilities of the hydrogen halides HC l, HBr and HI. [2]

3 ©YIJC [Turn over BLANK PAGE

4 ©YIJC [Turn over (c) Chlorine dioxide, ClO2 was discovered in 1811 and has been widely used for bleaching purposes in the paper industry and for treatment of drinking water. (i) ClO2 can be synthesised from the reaction between NaClO3 and H2O2 in an acidic medium. Construct a balanced equation for the reaction between ClO3− and H2O2. [2] (ii) In the process of handling ClO2, the concentration of the ClO2 in aqueous solution must not exceed 45 parts per million by mass, as it will cause irritation to the eyes and nose. 1 part per million can be expressed as 1 mg of the substance in 1 kg of water. An aqueous solution of C lO2 was prepared by adding 150 cm 3 of 1.0  103 mol dm−3 NaClO3 to 100 cm3 of 2.0  103 mol dm3 H2O2. Using your equation in (c)(i), calculate the concentration of the ClO2(aq) in parts per million, State whether it has exceeded the safety limit. [Assume the density of the final solution is 1 g cm3.] [3] The electrode potential for the reduction of chlorine dioxide is shown. ClO2(aq) + 4H+(aq) + 5e− ⇌ Cl−(aq) + 2H2O(l) Eo = +1.50V (iii) State what is meant by the term standard electrode potential. [1] (iv) Draw a fully labelled diagram of the electrochemical cell you would set up in order to measure the standard reduction potential of ClO2/Cl− in the laboratory. Indicate clearly the positive and negative electrodes. [3] Another cell composing of a standard ClO2/Cl half-cell and a standard Fe 3+/Fe2+ half- cell was set up. (v) Calculate ΔGo, in kJ mol–1, for the reaction that occurs [2] (vi) State and explain what happens to the standard cell potential, Eocell, when chlorine gas is bubbled into the Fe3+/Fe2+ half-cell. [2]

5 ©YIJC [Turn over

6 ©YIJC [Turn over (d) Describe and explain the relative ease of hydrolysis of chloroethane, chlorobenzene and ethanoyl chloride. [3] [Total: 20]

7 ©YIJC [Turn over BLANK PAGE

8 ©YIJC [Turn over 2 (a) Propanone reacts with iodine in acidic conditions as shown below. CH3COCH3(aq) + I2(aq)  CH3COCH2I(aq) + HI(aq) The rate of the reaction may be followed by measuring the concentration of the iodine at regular time intervals. Four separate sets of experiments were carried out in which the initial concentrations of the reactants were varied as shown in Table 2.1. Table 2.1 experiment initial concentration × 102 / mol dm3 propanone hydrochloric acid iodine 1 5 5 5 2 5 5 10 3 2 5 5 4 5 10 5 The results of experiment 1 and 2 are shown in Figure 2.1. time / min Fig. 2.1 0 1 2 3 4 5 6 7 8 9 10 11 0 10 20 30 40 50 60 70 80 experiment 2 experiment 1 [I2] × 102 / mol dm3

9 ©YIJC [Turn over The results shown in Table 2.2 were obtained for experiment 3 and 4. Table 2.2 experiment initial rate / mol dm3 min1 3 2.70  10–4 4 1.25  10–3 (i) Using Fig. 2.1, determine the order of reaction with respect to [I2]. Draw clearly any construction lines on Fig. 2.1 and show all your working. [1] (ii) Determine the orders with respect to [H+] and [CH3COCH3] [2] (iii) Hence write the rate equation for the reaction, and calculate a value of the rate constant. Include units in your answer. [3] (iv) The reaction of propanone with iodine proceeds via a three-step mechanism. The first step is the protonation of propanone, which is a fast step. The second step is the deprotonation of the intermediate formed in the first step to produce another intermediate, CH2=C(OH)CH3. Suggest a mechanism, which is consistent to your rate equation in (a)(iii) and indicate the rate determining step. The use of curly arrows is not required. [3]

10 ©YIJC [Turn over