2020 ACJC Prelim Paper 1 worked solutions

1 © ACJC2020 9729/01/Prelim/2020 ANGLO-CHINESE JUNIOR COLLEGE DEPARTMENT OF CHEMISTRY Preliminary Examination CHEMISTRY 9729/01 Higher 2 Paper 1 Multiple Choice 16 September 2020 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, index number and tutorial class on the Answer Sheet in the spaces provided unless this has been done for you. 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 15 printed pages and 1 blank page. 9729/01/Prelim/2020 ANGLO-CHINESE JUNIOR COLLEGE © ACJC 2020 Department of Chemistry [Turn over

2 © ACJC2020 9729/01/Prelim/2020 1 B 11 B 21 D 2 D 12 B 22 D 3 A 13 D 23 C 4 B 14 C 24 B 5 C 15 C 25 C 6 A 16 B 26 A 7 C 17 C 27 D 8 D 18 B 28 A 9 A 19 A 29 B 10 D 20 D 30 C 1 In July 2020, some households in Singapore reported a Pandan smell in their tap water. This was caused by an organic solvent tetrahydrofuran, THF , which has the following structure. The laboratory found that the concentration of THF in the Pandan smelling water was less than 10 ppb (10 parts per billion) by mass, which was significantly lower than the levels of THF that would cause health concerns. What is the concentration of 10 ppb of THF in mol dm3? Given:  1 billion = 109  density of water = 1.0 g cm3 A 1.39 x 1010 B 1.39 x 107 C 1.56 x 107 D 6.40 x 104 Answer: B Mr of THF = (12 x 4) + (1 x 8) + 16 = 72.0 In 109 g of water, there is 10g of THF (10ppb) 1 dm3 = 1000 cm3 of water Since density is 1.0 gcm3 1000 cm3 of water is 1000 g Hence, in 1000 g of water, mass of THF = 9 10 100010  = 1.00 x 105 g

3 © ACJC2020 9729/01/Prelim/2020 Amount of THF = 1.00 x 105 72.0 = 1.39 x 107 mol dm3 2 Use of the Data Booklet is relevant to this question. The approximate