2023 TJC H2 Chem Prelim P1 (Ans)

9729 / TJC PRELIM / 2023 TEMASEK JUNIOR COLLEGE 2023 JC2 PRELIMINARY EXAMINATION Higher 2 [Worked Solutions] CHEMISTRY 9729/01 Paper 1 Multiple Choice 18 September 2023 1 hour Additional Materials: Multiple Choice Answer Sheet Data Booklet READ THESE INSTRUCTIONS FIRST Write in soft pencil. Do not use staples, paper clips, glue or correction fluid. There are thirty questions on this paper. Answer all questions. For each question there are four possible answers A, B, C, D. Choose the one you consider correct and record your choice in soft pencil on the separate Answer sheet. Read the instructions on the Answer sheet very carefully. Write your name & Civics Group on the Answer sheet. Shade your index number in the appropriate boxes. Each correct answer will score one mark. A mark will not be deducted for a wrong answer. Any rough working should be done in this booklet. The use of an approved scientific calculator is expected, where appropriate. This document consists of 15 printed pages and 1 blank page. Write your name and Civics Group Last 4 digits of entry proof index number

2 2 MCQ ANSWERS (A:8, B:8, C:8, D:6) 1 2 3 4 5 6 7 8 9 10 C C C C A B C A B D 11 12 13 14 15 16 17 18 19 20 B B A B D C A D C B 21 22 23 24 25 26 27 28 29 30 A D A D A B C A B D 1 Magnesium thiocyanate, Mg(SCN) 2, has been found to support heart health by promoting healthy blood circulation and maintaining normal blood pressure levels. What are the numbers of electrons in the magnesium ion and the thiocyanate ion? Magnesium ion Thiocyanate ion A 12 29 B 10 29 C 10 30 D 10 31 Answer: C Worked Solution: No. of electrons in Mg2+ ion = 12 – 2 = 10 No. of electrons in SCN− ion = 16 + 6 + 7 + 1 = 30 2 In which pair of species do both species have only one unpaired p electron? 1 Ar− and F 2 Ar+ and Si+ 3 Ga and C−

3 9729 / TJC Prelim / 2023 [Turn over A 1 and 2 only B 2 and 3 only C 2 only D 3 only Answer: C (2 only) Worked Solution: Atoms and ions of electronic configuration of Group 13 and 17 elements will have only one unpaired electron. For reference Atom Group Electronic configuration of atom Electronic configuration of ion Ga 13 [Ar] 3d104s24p1 C/Si 14 s2p2 C−: 1s22s22p3 Si+: [Ne] 3s23p1 F 17 Is22s22p5 Ar 18 [Ne] 3s23p6 Ar+: [Ne] 3s23p5 Ar−: [Ne] 3s23p64s1 3 The 68Ga isotope is used in positron emission tomography (PET) scan to detect tumors. The radioactive decay of 68Ga isotope has a half-life of 68 days and produces the neutral particle, 68X. This transformation of 68Ga occurs with a proton changing into a neutron. Which of the following statement is incorrect? A 68X has 38 neutrons. B 68X is an isotope of zinc. C There are 3 electrons in the valence shell of 68X. D 2.42 % of the original 68Ga isotope remains after a year. Answer: C Worked Solut