2024 TJC Prelims H1 Paper 2 Structured Qns and Ans

8873 / TJC Prelims / 2024 DO NOT WRITE IN THIS MARGIN [Turn over TEMASEK JUNIOR COLLEGE 2024 JC2 PRELIMINARY EXAMINATION Higher 1 CANDIDATE NAME MARK SCHEME CENTRE NUMBER S INDEX NUMBER Chemistry 8873/02 Paper 2 Structured Questions 21 August 2024 2 hours Candidates answer on the Question Paper. Additional Materials: Data Booklet READ THESE INSTRUCTIONS FIRST Write your Centre number, index number and name in the spaces provided at the top of this page. 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. Section A Answer all the questions. Section B Answer one question. The use of an approved scientific calculator is expected, where appropriate. The number of marks is given in bracket [ ] at the end of each question or part question. This document consists of 23 printed pages and 1 blank page. For Examiner’s Use MCQ / 30 Section A Q1 / 8 Q2 / 8 Q3 / 12 Q4 / 10 Q5 / 10 Q6 / 12 Section B Q7 / 20 Q8 / 20

2 DO NOT WRITE IN THIS MARGIN 8873 / TJC Prelims / 2024 DO NOT WRITE IN THIS MARGIN DO NOT WRITE IN THIS MARGIN DO NOT WRITE IN THIS MARGIN Section A Answer all the questions in this section in the spaces provided. 1 This question is about copper-containing species. (a) Copper can exist as a number of isotopes. Some copper isotopes are unstable but are potentially useful for nuclear medicine. (i) Complete Table 1.1 for two isotopes of copper. [2] Table 1.1 isotopes protons neutrons electrons 63 29Cu 29 34 [✓] 29 67 29Cu [✓] 29 38 29 Cu isotope and neutrons 2✓ = [1] All protons, electrons (29) [1] (b) Tumbaga is an alloy of copper and gold. A sample of tumbaga was analysed and the composition of the isotopes present in the sample are shown in Table 1.2. Table 1.2 Mass number % abundance 63 56.4 65 x 197 18.5 (i) Determine the percentage abundance, x, of the species of mass number 65. [1] x = 100 – 56.4 – 18.5 = 25.1 [1] (ii) Hence, calculate the relative atomic mass, Ar, of the copper present in this sample of tumbaga. [1] Ar of Cu = (56.4 63) (25.1 65) 56.4 25.1  +  + = 63.6 [1] Common mistake: included gold in the calculation. (c) Brass is an alloy of copper and zinc. The percentage of mass of copper varies from 50% to 85%, depending on the properties needed in the alloy. A series of reactions is carried out in the laboratory to determine the percentage of copper in a sample of brass. 0.30 g of brass is dissolved in acid to give 100.0 cm3 of solution in which all copper is present as Cu 2+ ions. 25.0 cm 3 of the solution is transferred to a conical flask using a pipette and reacted with excess potassium iodide, K I. All the copper is precipitated as Cu I solid and iodine is formed. The iodine requires 21.50 cm3 of 0.0