2024 PU2 H1 Chem Paper 2 (ANS)_M1

Class Adm No Candidate Name: This question paper consists of 18 printed pages and 2 blank pages. 2024 Preliminary Exams Pre-University 2 H1 CHEMISTRY 8873/02 Paper 2 Structured Questions 9 Sep 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. Section A Answer all the questions. Section B Answer one question. 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 Section A Section B Total 1 2 3 4 5 6 7 Marks 11 18 16 6 9 20 20 80 H

2 Section A Answer all the questions in this section in the spaces provided. 1 Silicon compounds are used in the production of glass, ceramics, and refractory materials. Silicon dioxide is a major component of glass and is used in a wide range of applications, including construction, optics, and consumer products. For Examiners’ Use (a) A sample of silicon contains three isotopes, as shown in Table 1.1. Table 1.1 Isotope Percentage abundance / % 28Si 92.23 29Si 4.67 30Si 3.1 (i) Define the term relative atomic mass of silicon. ………………………………………………………………………………………………… [1] Weighted average mass of a silicon atom compared to 1/12 the mass of a 12C atom. (ii) Calculate the relative atomic mass of silicon from this sample, giving your answer in two decimal places. [1] Relative atomic mass of silicon = [(92.23 x 28) + (4.67 x 29) + (3.1 x 30)] / 100 = 28.11 (b) (i) State the full electronic configuration of silicon. Si : .…………………………………………………………………………………………… [1] 1s2 2s2 2p6 3s2 3p2 (ii) With reference to the Data Booklet, compare the values of second and third ionisation energies of silicon. Explain why these two energies are different and include an equation representing the third ionisation energy of silicon in your answer. …………………………………………………………………………………………………… ……………………………………………………………………………………………………

3 [Turn over ………………………………………………………………………………………………… [3] Si2+(g) → Si3+(g) + e- 2nd IE of Si: 1580 kJ mol-1 3rd IE of Si: 3230 kJ mol-1 The third IE of Si is larger than its second ionisation energy because the remaining electrons are closer to, and less shielded from