NJC_2022_H2_Chemistry_Prelim_P3_Ans

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 4 /20 5 /20 Paper 3 Total /80 This document consists of 28 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. Fig. 1.1 (i) Suggest the structure for compounds 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 25oC, are shown in table 1.2. Table 1.2 base Kb/moldm−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] …………………………………………………………………………………………….. …………………………………………………………………………………………….. …………………………………………………………………………………………….. CH3 CH2Cl Compound H CH2NH2 CH2Cl H2N Step 1 Step 2Step 3 Compound J Compound K (i) 1 or 0 (ii) Step1: UV light, limited Cl2. 1 or 0 Step 2: ethanolic NH3, heat in sealed tube. Step 3: conc H 2SO4, Conc HNO 3, 60oC (−CH2Cl has negligible effect on benzene) -accept T lower than 60oC. Step 4: conc HCl, Sn, heat followed by NaOH(aq) or (step 1 then 2) 1 or 0 for each step Step 4

3 NJC/H2 Chem Preliminary Examination/03/2022 [Turn over ……………………………………………………………………………………….. (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. 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