2021 CJC H2 CHEM Prelim P1 WORKED solutions to be uploaded

1 9729/01 CJC JC2 Preliminary Examination 2021 CANDIDATE NAME CLASS 2T CHEMISTRY 9729/01 Paper 1 Multiple Choice September 2021 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. Write your name, class and NRIC/FIN number on the Answer Sheet in the spaces provided. There are thirty questions on this paper. Answer all questions. For each question there are four possible answers A, B, C and 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. 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 12 printed pages. Catholic Junior College JC 2 Preliminary Examinations Higher 2 WORKED SOLUTIONS General comments Students found questions 2, 3, 14, 18, 19, 20, 22, 23, 24, 25, and 30 to be the most challenging. (You should revisit and fully understand these even you got it correct)

2 9729/01 CJC JC2 Preliminary Examination 2021 1 Nitrogen exists as a diatomic molecule, N 2. Hydrazine, N2H4, and dinitrogen difluoride, N2F2, are compounds of nitrogen. Which of the following gives the correct number of  bonds in N2, N2H4 and N2F2? number of  bonds in N2 number of  bonds in N2H4 number of  bonds in N2F2 A 2 0 1 B 2 1 1 C 1 1 2 D 3 0 2 (Inspired by H1 2020 MCQ6) Concept: Chemical Bonding,  and  bonds Answer: A number of  bonds in N2 number of  bonds in N2H4 number of  bonds in N2F2 (either cis or trans) A (1), 2 (5), no  (3), 1 2 Aluminium chloride is a covalent compound that forms a dimer with the formula Al2Cl6. A compound of gold and chlorine has a similar molecular formula of Au2Cl6 and has the following structure: The three statements below are properties of the gold compound, Au2Cl6. 1 The oxidation state of the metal is +3. 2 The dimer exists in the vapour phase. 3 The Cl-Au-Cl bond angle is 90o. Which property described is different from that of the aluminium compound, Al2Cl6? A 1 and 2 only B 1, 2 and 3 C 3 only D 2 and 3 only

3 9729 CJC JC2 Preliminary Exam 2021 [Turn over (Inspired by H2 2018 MCQ2) Concept: Chemical Bonding, Al2Cl6. Answer: C 1. This is a similar property to Al2Cl6. Chlorine is more electronegative than Al. Each Al also has an oxidation state of +3 as each Cl has an oxidation state of -1. 2. This is a similar property to Al2Cl6. Al2Cl6 dimer exists in the gas phase. 3. Not similar. The Cl-Al-Cl bond angle is 109.5o. 3 The table below lists three compounds: compound boiling p