2023 SAJC H2 Chem Prelim P1 (Ans)

ST ANDREW’S JUNIOR COLLEGE JC2 PRELIMINARY EXAMINATIONS HIGHER 2 CANDIDATE NAME CLASS 2 2 S CHEMISTRY Paper 1 Multiple Choice Additional Materials: Multiple Choice Answer Sheet Data Booklet 9729/01 15 September 2023 1 hour READ THESE INSTRUCTIONS FIRST Write in soft pencil. Do not use staples, paper clips, glue or correction fluid. Write your name and class 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. 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 XX printed pages (including this cover page) and 1 blank page.

1 The relative atomic mass of boron, which consists of the isotopes 10 5 B and 11 5 B is 10.8. What is the percentage of 11 5 B atoms in the isotopic mixture? A 0.2 % B 0.8% C 20 % D 80 % Ans: D Let x be the relative abundance of 11 5 B 11 x + 10 (1−x) = 10.8 X = 0.8 Hence % abundance = 0.8 x 100 = 80% 2 A mixture of sodium iodide, 23Na127I, and sodium bromide, 23Na79Br, were vapourised and the ions passed through an electric field. Which statements about the results are correct? 1 There would be 4 angles of deflections observed. 2 The particle with the largest angle of deflection will be detected at the negative plate. 3 The positive plate will detect more particle types than the negative plate. A 1 only B 2 and 3 only C 1 and 2 only D 1,2 and 3 Ans: B When the mixture is vapourised, there are only 3 different particle types, Na +, I− and Br−. Hence, only 3 angle of deflections will be obtained. Statement 1 is wrong. The (charge/mass) of the 3 particles are Na+= 0.0435, I−= 0.00787 and Br−= 0.0127. Therefore, Na+ will give the largest angle of deflection, which will be detected at the negative place. Hence statement 2 is correct. Since there are 2 anions and 1 cation, the positive plate will detect one more particle type as compared to the positive place. Statement 3 is correct.

3 [TURN OVER 3 Which of the following statements about ice and its structure is correct? A The bond angle around O in ice is 109.5°. B Ice is more dense than water. C 2 electrons on O in ice are involved in hydrogen bonding. D Hydrogen bonds formed in ice are as strong as the O-H covalent bonds. Ans: A Ice has an open structure where each O is covalently bonded to 2 H atoms and the 2 lone pairs (4 electrons) each form a hydrogen bond with 2 other neighboring water molecules. (option C is thus incorrect). This leads to O being tetrahedrally bonded to 4 H atoms and thus have a bond angle of 109.5°