2020 JPJC Prelim Paper 2 answers

NAME CLASS 19S JURONG PIONEER JUNIOR COLLEGE JC2 PRELIMINARY EXAMINATION 2020 CHEMISTRY 9729/02 Higher 2 Paper 2 Structured Questions 17 September 2020 2 hours Candidates answer on the Question Paper. Additional Materials: Data Booklet READ THESE INSTRUCTIONS FIRST Write your name, class and exam 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 a HB pencil for any diagrams, 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 Question Mark 2 1 13 2 9 3 14 4 12 5 6 6 21 Penalty (delete accordingly) Lack 3sf in final ans –1 / NA Missing/wrong units in final ans –1 / NA Total 75 This document consists of 21 printed pages.

2  Jurong Pioneer Junior College 9729/02/J2 Prelim/2020 Answer all the questions in the spaces provided. 1 (a) The following graph below shows the second ionisation energies of Period 3 elements with consecutive proton number. For Examiner’s Use (i) Explain why the second ionisation energy generally increases from B to H. Across the period, the nuclear charge/ proton number increases and the radius decreases while the shielding effect is relatively constant (due to same number of inner shell electrons). Hence, increase in effective nuclear charge OR nuclear attraction on the electron to be removed increases and hence, the second IE generally increases. [2] (ii) Which of the above elements, A to H, is aluminium? Element C [1] (iii) Explain the following:  big drop in second ionisation energy from A to B  slight drop in second ionisation energy from C to D A to B: 2nd ionisation energy involves removal of 3s electron from B+ and removal of 2p electron in A+. B+ has 1 more quantum shell with electrons thus the electron to be removed from H + is further away from nucleus, hence the nuclear attraction on the electron to be removed is weaker and hence, the 2nd IE of B is much lower than that of A. C to D: C+: ns2 D+: ns2 np1 The np electron removed from D+ is further away from the nucleus and has a higher energy than the ns electron removed from C+. Thus more energy is required to remove it. [2] 0 500 1,000 1,500 2,000 2,500 3,000 3,500 4,000 4,500 5,000 C D E F G H A B 2nd Ionisation Energy/