23MIPrelim Answers (H2 Chem Paper 1)

Class Adm No Candidate Name: This question paper consists of 14 printed pages and 2 blank pages. 2023 Preliminary Examination Pre-University 3 H2 CHEMISTRY 9729/01 Paper 1 Multiple Choice 20th Sep 2023 1 hour Additional materials: Multiple Choice Answer Sheet Data Booklet READ THESE INSTRUCTIONS FIRST Do not turn over this question paper until you are told to do so Write in soft pencil. Do not use staples, paper clips, glue or correction fluid. Write your name, class and admission number in the spaces provided at the top of this page and on the Multiple Choice Answer Sheet 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 Multiple Choice Answer Sheet provided. Read the instructions on the Multiple Choice 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 question paper. The use of an approved scientific calculator is expected, where appropriate. FOR EXAMINER’S USE TOTAL (30 marks)

2 1 A 6 D 11 C 16 B 21 C 26 B 2 C 7 B 12 D 17 D 22 D 27 C 3 D 8 C 13 A 18 D 23 A 28 C 4 D 9 B 14 B 19 A 24 B 29 B 5 B 10 C 15 D 20 C 25 A 30 A Total: A 6 B 8 C 8 D 8 For each question there are four possible answers, A, B, C, and D. Choose the one you consider to be correct. 1 Which of the following contain the same number of hydrogen atoms? 1 0.10 mol of pentane 2 0.15 mol of but-2-ene 3 0.60 mol of hydrogen gas 4 0.50 mol of steam A 1, 2 and 3 only B 1 and 4 only C 2 and 4 only D 1 and 2 only Pentane is C5H12 amt of H atoms = 0.10 × 12 = 1.2 mol But-2-ene is C4H8 amt of H atoms = 0.15 × 8 = 1.2 mol H2 amt of H atoms = 0.60 × 2 = 1.2 mol H2O amt of H atoms = 0.5 × 2 = 1.0 mol (A)

3 [Turn over 2 Ascorbic acid found in fruits and vegetables is believed to help prevent colds. Analysis of ascorbic acid shows that it contains only carbon, hydrogen and oxygen with 40.91% carbon and 4.55% hydrogen by mass. Ascorbic acid has a molar mass of 176 g mol–1. What is the molecular formula of ascorbic acid? A C2H3O2 B C3H4O3 C C6H8O6 D C6H9O6 Draw up the empirical formula table first C H O % by mass 40.91 4.55 100–40.91– 4.55 = 54.54 amt 40.91/12.0 4.55/1.0 54.54/16.0 =3.409 =4.55 3.409 Simplest ratio 1 = 3 1.33 = 4 3 = 3 Empirical formula = C3H4O3 Let molecular formula be (C3H4O3)x x (3×12.0 + 4 × 1.0 + 3 × 16.0) = 176 x = 2 Hence molecular formula is C6H8O6. Note: 1.33 for H should not be rounded to 1.5 because 1.33 is equivalent to 4/3 hence all values should be multiplied by 3 throughout. (C)