2024 MI PU3 MYE P2 (student)

Class Adm No Candidate Name: This question paper consists of 16 printed pages and 2 blank pages. 2024 Mid-Year Exams Pre-University 3 H2 CHEMISTRY 9729/02 Paper 2 Structured Questions 28 June 2024 2 hours Candidates answer on the Question paper. Additional materials: Data Booklet READ THESE INSTRUCTIONS FIRST Do not turn over this question paper until you are told to do so. Write your name, class and admission number on all the work you hand in. Write in dark blue or black pen. You may use an HB pencil for any diagrams or graphs. Do not use staples, paper clips, glue or correction fluid. Answer all questions. The use of an approved scientific calculator is expected, where appropriate. A Data Booklet is provided. At the end of the examination, fasten all your work securely together. The number of marks is given in brackets [ ] at the end of each question or part question. Question 1 2 3 4 5 Total Marks 15 16 15 16 13 75

2 Answer all questions. 1 Ibuprofen, aspirin, and paracetamol are commonly sold as over -the-counter painkillers that offer versatile relief for different forms of pain. Table 1.1 shows the physical properties of the painkillers and some organic compounds. For Examiners’ Use Table 1.1 compound Mr melting point / °C solubility in water / g dm–3 solubility in ethanol / g dm–3 density / g cm–3 ibuprofen (C13H18O2) 206.0 75 0.021 1.2 1.03 aspirin (C9H8O4) 180.0 135 3.0 80 1.40 paracetamol (C8H9NO2) 151.0 169 12.8 130 1.26 phenol (C6H6O) 94.0 40.5 84.2 highly soluble 1.07 ethanoyl chloride (C2H3OCl) 78.5 –112 – – 1.10

3 [Turn over A student was provided with three unlabelled tablets, one from each of the three different painkillers. To identify them, he crushed each of the tablets and dissolved them in ethanol. To a small portion of each solution, he conducted two simple chemical tests to distinguish between the painkillers. For Examiners’ Use (a) (i) Define the term relative molecular mass, Mr. …………………………………………………………………………………………………… …………………………………………………………………………………………………… ………………………………………………………………………………………………… [1] (ii) Suggest, briefly, two reasons for the difference in solubilities between ibuprofen and paracetamol in water. …………………………………………………………………………………………………… …………………………………………………………………………………………………… …………………………………………………………………………………………………… …………………………………………………………………………………………………… …………………………………………………………………………………………………… ………………………………………………………………………………………………… [2] (iii) Suggest the reagents and conditions, stating the observations, for the two simple chemical tests used to distinguish between ibuprofen, aspirin, and paracetamol. …………………………………………………………………………………………………… …………………………………………………………………………………………………… …………………………………………………………………………………………………… …………………………………………………………………………………………………… …………………………………………………………………………………………………… …………………………………………………………………………………………………… …………………………………………………………………………………………………… ………………………………………………………………………………………………… [4]

4 (b) The student planned to synthesise aspirin from phenol and ethanoyl chloride (in 1 : 2 molar ratio) via an acylation reaction to form an intermediate A, before turning it into aspirin under controlled conditions in step 2. The liquid ethanoyl chloride was measured out using a graduated gas syringe and added to phenol in an inert solvent. For Examiners’ Use (i) Suggest a catalyst for step 1. ………………………………………………………………………………………………… [1] (ii) Draw the structure of the intermediate A. [1] (iii) State the reagents and conditions for step 2. …………………………………………………………………………………………………… ………………………………………………………………………………………………… [1] (iv) Calculate the volume of ethanoyl chloride that is needed to completely react with 4.00 g of phenol to form aspirin using the suggested synthetic pathway in (b)(i). [3]

5 [Turn over (v) The resultant aspirin product was washed, dried, and weighed. Given that 5.57 g of aspirin was formed, calculate the percentage yield of the reaction. [1] For Examiners’ Use (vi) Suggest why there are no solubility values for ethanoyl chloride. …………………………………………………………………………………………………… ………………………………………………………………………………………………… [1] [Total: 15]

6 2 (a) Arrange the following molecules in increasing order of gas phase relative basic strength , explaining your answer. ………………………………………………………………………………………………………… ………………………………………………………………………………………………………… ………………………………………………………………………………………………………… ………………………………………………………………………………………………………… ………………………………………………………………………………………………………… ………………………………………………………………………………………………………… ………………………………………………………………………………………………………… ………………………………………………………………………………………………………… ……………………………………………………………………………………………………... [4] For Examiners’ Use (b) Ethylamine, CH3CH2NH2, can be formed from ethane, CH3CH3, via the following steps. Step 1: Free radical substitution of ethane to form chloroethane. Step 2: Nucleophilic substitution of chloroethane to ethylamine. (i) Outline the mechanism for step 1. Draw curly arrows to show the movement of electrons. [3]

7 [Turn over (ii) Suggest the reagents and conditions for step 2. …………………………………………………………………………………………………… ………………………………………………………………………………………………… [1] For Examiners’ Use (c) Phenylamine, C6H5NH2, can be synthesised from benzene. (i) Suggest the reagents and conditions for steps 1 and 2 and state the type of reaction in each step. Step 1: …………………………………………………………………………………………... …………………………………………………………………………………………………… Step 2: …………………………………………………………………………………….......... ………………………………………………………………………………………………… [4] (ii) After step 2, a colourless solution containing phenylammonium ions, C 6H5NH3+, was obtained. Upon addition of NaOH(aq), solid crystals of phenylamine , C 6H5NH2, precipitated out of the colourless solution. Explain the observations in terms of the interactions between particles. …………………………………………………………………………………………………… …………………………………………………………………………………………………… …………………………………………………………………………………………………… …………………………………………………………………………………………………… …………………………………………………………………………………………………… ………………………………………………………………………………………………… [2]

8 (d) The Hofmann degradation is an organic rearrangement reaction of a primary amide to a primary amine with the loss of one carbon atom. The reagent is heated under reflux with bromine in sodium hydroxide to transform the primary amide into an isocyanate intermediate, which is subsequently hydrolysed to a primary amine. Suggest the amide used to produce the following products via the Hoffmann degradation. For Examiners’ Use (i) → CH3CH2NH2 [1] (ii) → [1] [Total: 16]

9 [Turn over 3 (a) Use of the Data Booklet is relevant for this question. For Examiners’ Use (i) Define the term first electron affinity of fluorine. …………………………………………………………………………………………………… ………………………………………………………………………………………………… [1] (ii) Potassium fluoride, KF, is a main source of fluoride ions for manufacturing and in chemistry. It is found in the mineral carobbiite. Use the data in Table 3.1 and relevant bond energy values from the Data Booklet to complete the Born-Haber cycle below and hence calculate the lattice energy for KF(s). Table 3.1 enthalpy change of formation, ΔHf, for KF(s) –561 kJ mol–1 enthalpy change of atomisation of potassium, K(s) +90 kJ mol–1 first electron affinity of fluorine –328 kJ mol–1 Energy / kJ mol–1 [5]