EJC 2020 JC2 Prelim H2 Chemistry Paper 2 QP

© EJC [Turn Over EUNOIA JUNIOR COLLEGE JC2 Preliminary Examination 2020 General Certificate of Education Advanced Level Higher 2 CANDIDATE NAME CIVICS GROUP 1 9 – INDEX NUMBER CHEMISTRY Paper 2 Structured Questions 9729/02 02 September 2020 2 hours Candidates answer on the Question Paper Additional Materials: Data Booklet READ THESE INSTRUCTIONS FIRST Write your name, civics group, index number 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. Answer all questions in the spaces provided on the Question Paper. 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. For Examiner’s Use Paper 2 1 / 12 2 / 12 3 / 18 4 / 16 5 / 17 Total / 75 This document consists of 21 printed pages and 1 blank page.

2 © EJC 9729/02/J2PE/20 For Examiner’s Use 1 (a) Nitrogen can form a few hydrides such as NH3 and N2H4. The boiling points of these two hydrides are given in Table 1.1. Table 1.1 compound boiling point / ºC NH3 −33 N2H4 114 Provide two explanations for why N2H4 has a higher boiling point than NH3. ................................ ................................ ................................ ................................ .... ................................ ................................ ................................ ................................ .... ................................ ................................ ................................ ................................ .... ................................ ................................ ................................ ................................ .... ................................ ................................ ................................ ................................ .... ................................ ................................ ................................ ................................ .... ................................ ................................ ................................ ................................ .... ................................ ................................ ................................ ................................ .... ................................ ................................ ................................ ................................ [2]

3 © EJC 9729/02/J2PE/20 [Turn over For Examiner’s Use (b) When NH3 is reacted with BF3 in the gaseous phase, a white solid of NH3BF3 is formed. (i) Draw a dot-and-cross diagram to show the bonding within NH3BF3 and state the shape about the nitrogen atom. shape ................................ ........................ [2] (ii) State the type of reaction that NH 3 has undergone with BF3, and explain why it is possible. ................................ ................................ ................................ ............................. ................................ ................................ ................................ ............................. ................................ ................................ ................................ ......................... [2] (c) Both NH3 and PH3 have trigonal pyramidal shape, but the bond angles in NH3 are 107º while those in PH3 are 94º. By considering the electronegativities of the central atoms, suggest why this is so. ................................ ................................ ................................ ................................ .... ................................ ................................ ................................ ................................ .... ................................ ................................ ................................ ................................ .... ................................ ................................ ................................ ................................ .... ................................ ................................ ................................ ................................ [2]

4 © EJC 9729/02/J2PE/20 For Examiner’s Use (d) Table 1.2 shows the successive ionisation energies of an element A. Table 1.2 ionisation energies / kJ mol−1 1st 2nd 3rd 4th 5th 6th 7th 8th 9th 10th element A 945 1794 2735 4839 6056 11690 14180 17370 20550 23830 (i) Explain why the successive ionisation energies of an element always increase. ................................ ................................ ................................ ............................. ................................ ................................ ................................ ............................. ................................ ................................ ................................ ............................. ................................ ................................ ................................ ......................... [1] (ii) Is element A likely to be from the same group as nitrogen? Explain your answer clearly. ................................ ................................ ................................ ............................. ................................ ................................ ................................ ............................. ................................ ................................ ................................ ............................. ................................ ................................ ................................ ............................. ................................ ................................ ................................ ............................. ................................ ................................ ................................ ......................... [2] (iii) State and explain how the first ionisation energy of element A will compare to that of the element to its right in the periodic table. ................................ ................................ ................................ ............................. ................................ ................................ ................................ ............................. ................................ ................................ ................................ ............................. ................................ ................................ ................................ ............................. ................................ ................................ ................................ ........................ [1] [Total: 12]

5 © EJC 9729/02/J2PE/20 [Turn over For Examiner’s Use 2 One widely recognised free radical i n the atmosphere that drives ozone depletion is the hydroxyl radical, HO•. The hydroxyl radicals can react with HCl molecules existing in the atmosphere to produce chlorine atoms , which may then play a role in catalysing ozone decomposition.  HO HC water C atom    ll To study the kinetics of the rate of reaction of hydroxyl radicals with a large excess of HCl, [HO•] was measured at regular time intervals at 300 K. The results are shown in Table 2.1. Table 2.1 time / ms 0.0 1.0 2.0 3.0 4.0 5.0 6.0 [HO•(g)] / × 10−9 mol dm–3 10.0 6.8 4.5 3.0 2.1 1.4 0.9 (a) Plot the graph of [HO•] against time on the grid in Fig. 2.1, and use the graph to show that the reaction is first order with respect to hydroxyl radicals.