2023 SOTA Yr 6 Chem HL Prelim Exam P3

Yr6/4/CHEM/HP3/Aug2023 12 pages © School of the Arts, Singapore CHEMISTRY Higher level Paper 3 Preliminary Examinations Tuesday 29 August 2023 1 hour 15 minutes INSTRUCTIONS TO CANDIDATES • Write your name, class and index number in the blanks below. • Do not open this examination paper until instructed to do so. • Answers must be written within the answer boxes provided. • A calculator is required for this paper. • A clean copy of the chemistry data booklet is required for this paper. • The maximum mark for this examination paper is [45 marks]. Section A Questions Answer all the questions. 1 –- 2 Section B Questions Answer all the questions. Option D -– Medicinal chemistry 3 –- 11 Name: Class: Index: 45

Yr6/4/CHEM/HP3/Aug2023 Turn over - 2 - Section A Answer all questions. Write your answers in the boxes provided. 1. A group of chemistry students read that fish is a good source of iodine in the form of iodide ions. They decided to extract the iodine from 600 g of fish. The students blended the fish in a food processor with 100 cm3 of water, left it to stand overnight and then filtered the mixture into a beaker. (a) One of the students suggested that the presence of iodide ions in the solution could be confirmed by adding silver nitrate solution. The silver ions reacted with iodide ions to form pale yellow silver(I) iodide precipitate. Formulate an ionic equation, including state symbols, for this reaction. [2] ………………………………………………………………………..………………………… ………………………………………………………………………..………………………… (b) 5 cm3 of dilute sulfuric acid and 5 cm3 of hydrogen peroxide solution were added to the filtrate containing iodide ions. Aqueous iodine was formed. (i) State the role of hydrogen peroxide solution in this reaction. [1] …………………………………………..……………………………………………………… (ii) Suggest the role of dilute sulfuric acid in this reaction. [1] …………………………………………..………………………………………………………

Yr6/4/CHEM/HP3/Aug2023 Turn over - 3 - (c) 25.00 cm3 of the aqueous iodine from (b) was titrated against 0.0010 mol dm-3 standard sodium thiosulfate solution. I2(aq) + 2S2O32-(aq) à 2I-(aq) + S4O62-(aq) The titration readings are tabulated as shown. Titration 1 Titration 2 Titration 3 Final burette reading / ±0.05cm3 5.20 10.10 15.40 Initial burette reading / ±0.05cm3 0.00 5.20 10.10 Volume of S2O32- used / ±0.10 cm3 5.20 4.90 5.30 (i) Determine the average titre value using the table above. [1] ………………………………………………………………………..………………………… ………………………………………………………………………..………………………… (ii) Calculate the percentage uncertainty using your answer obtained in (c)(i). [1] ………………………………………………………………………..………………………… ………………………………………………………………………..………………………… (iii) Suggest how the experiment could be modified to improve the precision of th