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 this investigation. [1] ………………………………………………………………………..………………………… ………………………………………………………………………..…………………………

Yr6/4/CHEM/HP3/Aug2023 Turn over - 4 - 2. Raoult’s Law states that the partial vapour pressure of a component of a liquid mixture is equal to the vapour pressure of the pure component multiplied by its mole fraction. The partial vapour pressure can be represented by the following equation: 𝑃!= c! × 𝑃!" where 𝑃! refers to the partial vapour pressure of a component (liquid A) in the mixture, c!( = #"$%& "( $)*+), !-"-.$ #"$%& "( $)*+),& ) refers to the mole fraction of a liquid in the mixture, and 𝑃!" refers to the vapour pressure of pure liquid A. An ideal solution is a mixture of liquids in which the intermolecular forces are the same as in the pure liquids. Hence the tendency for a liquid to evaporate is the same in the pure liquid as in the solution. For a solution consisting of two miscible components, liquid A and liquid B, the total pressure, P may be expressed as P = 𝑃! + 𝑃𝐵 = c!×𝑃!" + c/×𝑃𝐵" The following graph shows the partial vapour pressure of an ethanol-water mixture at different mole fractions of ethanol. (a) State the vapour pressure of pure water. [1] 𝑃0.-%1" : ……………………………………………………………………..………………….. Vapour pressure / kPa ethanol water total pressure Mole fraction of ethanol

Yr6/4/CHEM/HP3/Aug2023 Turn over - 5 - (b) Predict how the vapour pressure of a liquid will be affected by an increase in temperature. [1] ………………………………………………………………………..………………………… ………………………………………………………………………..………………………… (c) Determine the total pressure of a mixture containing 40% ethanol and 60% water. [1] ………………………………………………………………………..………………………… ………………………………………………………………………..………………………… (d) Using information from the graph, explain why ethanol is a more volatile liquid. [1] ………………………………………………………………………..………………………… ………………………………………………………………………..………………………… ………………………………………………………………………..………………………… (e) (i) Suggest two reasons why ethanol vapour is not behaving as an ideal gas. [2] ………………………………………………………………………..………………………… ………………………………………………………………………..………………………… ………………………………………………………………………..………………………… ………………………………………………………………………..………………………… ………………………………………………………………………..………………………… (ii) On the graph below, sketch the graph to show the partial vapour pressure of ethanol if it behaves as an ideal solution. [2] Vapour pressure / kPa Mole fraction of ethanol

Yr6/4/CHEM/HP3/Aug2023 Turn over - 6 - Section B Answer all the questions. Write your answers in the boxes provided. Option D --- Medicinal Chemistry 3. Drugs are tested to determine their safety and effectiveness before they are sold to the public. (a) Distinguish between toxic dose (TD50) and lethal dose (LD50). [2] ………………………………………………………………………..………………………… ………………………………………………………………………..………………………… ………………………………………………………………………..………………………… ………………………………………………………………………..………………………… ………………………………………………………………………..………………………… (b) The therapeutic index of a drug is 1.5. Comment on the risk of overdose when taking the drug. [1] ………………………………………………..………………………………………………… ………………………………………………………..………………………………………… (c) State the method of drug administration that gives the maximum bioavailability. [1] ………………………………………………..………………………………………………… ………………………………………………………..………………………………………… (d) Suggest one ethical consideration faced by pharmaceutical companies when developing drugs. [1] ………………………………………………..………………………………………………… ………………………………………………………..…………………………………………

Yr6/4/CHEM/HP3/Aug2023 Turn over - 7 - 4. Salicylic acid has been used to relieve pain and reduce fever, but it causes severe irritation of the stomach lining. Its molecular structure is shown below. (a) Suggest one reactant used to prepare aspirin from salicylic acid. The structure of aspirin is shown in section 37 of the data booklet. [1] ………………………………………………..………………………………………………… ………………………………………………………..………………………………………… (b) Suggest why aspirin is slightly soluble in water by referring to its structure. [2] ………………………………………………………………………..………………………… ………………………………………………………………………..………………………… ………………………………………………………………………..………………………… ………………………………………………………………………..………………………… ………………………………………………………………………..………………………… (c) Formulate an equation for the conversion of aspirin to a more water-soluble derivative. [1]

Yr6/4/CHEM/HP3/Aug2023 Turn over - 8 - (d) The infrared spectra for salicylic acid and aspirin are shown. Salicylic acid Aspirin [Source: https://sdbs.db.aist.go.jp/]

Yr6/4/CHEM/HP3/Aug2023 Turn over - 9 - Compare and contrast the two spectra with respect to the bonds present, using information from section 26 of the data booklet. [3] Similarities: …………………………………………………..……………………………………………… …………………….……………………………….…………………………………………… …………………………….……………………….…………………………………………… …………………………………….