2024 Prelims ACJC H2 Chem P2 (Ans)

This paper consists of 22 printed pages and 2 blank pages. Anglo-Chinese Junior College JC2 Preliminary Examination Higher 2 CANDIDATE NAME Answers FORM CLASS TUTORIAL CLASS INDEX NUMBER CHEMISTRY Paper 2 Structured Questions Candidates answer on the Question Paper. Additional materials: Data Booklet 9729/02 21 August 2024 2 hours READ THESE INSTRUCTIONS FIRST Write your form class, index number and name in the spaces provided at the top of this page. 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. The number of marks is given in brackets [ ] at the end of each question or part question. For Examiner's Use Question no. Marks 1 / 12 2 / 11 3 / 10 4 / 10 5 / 10 6 / 22 Presentation of answers TOTAL / 75

© ACJC2024 9729/Mid-Year Learning Checkpoint/2024 Section B: Structured Questions (75 marks) Answer all the questions in the spaces provided. 1 Y and Z are two elements found in Period 3. Their fifth to eighth ionisation energies are given in Table 1.1. Table 1.1 successive ionisation energies / kJ mol–1 5th 6th 7th 8th Y 6530 9353 11019 33606 Z 7004 8496 27107 31719 (a) (i) State and explain the group number of Y. [1] Y belongs to Group 17. There is a large jump between the 7th and 8th ionisation energies, so the 8th electron to be removed comes from an inner (principal quantum) shell. [1] Comments • Generally well done. However, many students misspelt ‘principal’ as ‘principle’. Also, the terms ‘principal quantum shell’ and ‘subshell’ should not be used interchangeably. (ii) Complete the electronic configurations of Y+ and Z+. Y+: 1s22s22p63s23p4 Z+: 1s22s22p63s23p3 Comments • Students should write out the electronic configuration of elements Y and Z first before removing an electron. (iii) From your answer in (a)(ii), explain why the second ionisation energy of Y is expected to be lower than Z. [1] The second ionisation energy for element Y involves removing a paired electron from the 3p subshell that has interelectronic repulsion while the second ionisation energy for element Z involves removing an unpaired electron from the 3p subshell. Comments • A significant number of students were able to identify that there was greater interelectronic repulsion in Y but did not mention this was due to the paired electrons. • For the 2 nd IE of Z, only the electrons in the 3p subshell are unpaired, the inner electrons are stil