NJC 2022 H2 Chemistry Prelim P3 QP

1 NJC/H2 Chem Preliminary Examination/03/2022 [Turn over NATIONAL JUNIOR COLLEGE SH2 PRELIMINARY EXAMINATION Higher 2 CANDIDATE NAME SUBJECT CLASS REGISTRATION NUMBER CHEMISTRY Paper 3 Free Response Candidates answer on Question Paper. Additional Materials: Data Booklet 9729/03 13 September 2022 2 hours READ THE INSTRUCTIONS FIRST Write your subject class, registration number and name on all the work you hand in. Write in dark blue or black pen. You may use a soft 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. A Data Booklet is provided. The use of an approved scientific calculator is expected, where appropriate. The number of marks is given in brackets [ ] at the end of each question or part question. For Examiner’s Use Section A 1 /18 2 /19 3 /23 Section B (*circle the question you attempt) 4 /20 5 /20 Paper 3 Total /80 This document consists of 32 printed pages.

2 NJC/H2 Chem Preliminary Examination/03/2022 Section A Answer all the questions in this section. 1 (a) Amines can be synthesised from methylbenzene, shown by the following steps. CH3 CH2Cl Compound H CH2NH2 CH2Cl H2N Step 1 Step 2Step 3 Compound J Compound K Fig. 1.1 (i) Suggest the structure for compound H. [1] (ii) Suggest reagents and conditions for steps 1, 2, 3 and 4 in Fig. 1.1. [4] (iii) Suggest why the yield for step 2 is not high. [1] The Kb values of three bases, at 25 oC, are shown in Table 1.2. Table 1.2 base Kb/mol dm−3 ammonia 1.8 x 10−5 compound K 4.5 x 10−4 compound J 7.4 x 10−10 (iv) Explain the relative magnitudes of the Kb values in Table 1.2. [2] …………………………………………………………………………………………….. …………………………………………………………………………………………….. …………………………………………………………………………………………….. …………………………………………………………………………………………….. …………………………………………………………………………………………….. …………………………………………………………………………………………….. Step 4

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4 NJC/H2 Chem Preliminary Examination/03/2022 (b) The rate of reaction for step 2 in Fig. 1.1 can be followed by measuring the change in concentration of C7H7Cl with time. The reaction was carried out with the other reactant in large excess. Fig. 1.2 shows the concentration of C7H7Cl monitored against time for step 2. Fig. 1.2 Showing all your working and drawing clearly any construction lines, use Fig.1.2 to determine: (i) The order with respect to C7H7Cl. Explain your reasoning. [2] (ii) The initial rate, in mol dm−3 min−1 [1] Given that the half -life magnitude of C7H7Cl is not affected by the change in concentration of the other reactant. (iii) Write the rate equation for step 2 in Fig.1.1, and calculate a value for the rate constant, stating its units. [2] (iv) Hence, outline a mechanism for step 2 in Fig.1.1 to form all the products. Show all charges and relevant lone pairs and show the movement of electron pairs by using curly arrows. [3] (v) Explain why step 2 proceeds via the mechanism you describe in b(iv). [1] (vi) Suggest and explain the difference in reactivity when 4-bromomethylbenzene undergoes the same reaction. [1] [Total : 18] 0 0.002 0.004 0.006 0.008 0.01 0.012 0.014 0.016 0.018 0.02 0 100 200 300 400 500 600 700 800 Time/min [C7H7Cl ] / mol dm-3

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7 NJC/H2 Chem Preliminary Examination/03/2022 [Turn over PLEASE TURN OVER

8 NJC/H2 Chem Preliminary Examination/03/2022 2 Hydrogen cyanide, HCN, is extremely toxic and with sufficient concentrations it leads to rapid death. During the Second World War, a form of hydrogen cyanide known as Zyklon B was used in the Nazi gas chambers. (a) (i) Draw a dot–and–cross diagram to illustrate the bonding in HCN. [1] HCN can be oxidised