2024 MI PU3 MYE P2 (Answers) with marker's comment

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] The weighted average mass of one molecule relative to the 1/12 the mass of a 12C atom. Marker’s comment: - Poorly done, many students wrote C12 (ii) Suggest, briefly, two reasons for the difference in solubilities between ibuprofen and paracetamol in water. [2] Stronger instantaneous dipole -induced dipole forces of attraction between ibuprofen molecules due to the larger electron cloud size (Mr = 202.0) than paracetamol molecules (Mr = 151.0) OR longer non-polar alkyl chain ; Paracetamol molecules form more extensive hydrogen bonding with water molecules (due to greater number of electronegative O, N atoms and lone pairs available) than ibuprofen molecules. ; Marker’s comment: - Very poor