H1 Chem P2_SAJC_2024_Ans

1 ST ANDREW’S JUNIOR COLLEGE PRELIMINARY EXAMINATIONS HIGHER 1 CANDIDATE NAME CLASS 2 3 H1 CHEMISTRY 8873 / 02 Paper 2 Structured Questions 27 August 2024 2 hours Candidates answer on the Question Paper. Additional Materials: Data Booklet READ THESE INSTRUCTIONS FIRST Write your centre number, index number, name and class at the top of this page. Write in dark blue or black pen. You may use a 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 brackets [ ] at the end of each question or part question. Question Number Total Marks Marks Obtained SECTION A 1 14 2 7 3 9 4 30 SECTION B 5 20 6 20 TOTAL 80 This document consists of XX printed pages (including this cover page).

2 Section A Answer all the questions in this section in the spaces provided. 1 This is a question about Group 14 elements and its compounds. (a) (i) A sample of silicon contains three isotopes, as shown in Table 1.1. Table 1.1 Isotope Relative Isotopic mass Percentage abundance. % 28Si 27.976 92.22 29Si 28.976 4.69 30Si 29.973 3.09 Calculate the relative atomic mass of silicon in this sample, giving your answer to two decimal places. [2] Relative atomic mass of silicon = (27.976 x 92.22 + 28.976 x 4.69 + 29.973 x 3.09 ) / 100 = 28.08 (to two decimal places) (ii) Complete the electronic configuration for silicon. [1] 1s2 …………………………… 1s2 2s22p63s23p2 (iii) Explain why second ionisation energy of silicon is lower than that of aluminium. [2] 2nd I.E. of Si is lower than that of Al. Al+: 1s2 2s2 2p6 3s2 Si+ : 1s2 2s2 2p6 3s2 3p1 • In Al+, the electron is removed from the 3s orbital, whereas for Si+, the electron is removed from the 3p orbital.

3 • The electron in the 3p orbital is further from the nucleus √ than the electron in the 3s orbital and experiences additional shielding effect√ by the two 3s electrons. • These factors outweigh the effect of increase in nuclear charge √ from Al+ to Si+, resulting in a weaker attraction by nucleus √ • Hence less energy is required to remove the electron from the 3p orbital in Si+ than that in the 3s orbital in Al+. (b) When carbon tetrachloride, CC l4, and silicon tetrachloride , SiC l4, were added to water, the following observations were seen. carbon tetrachloride Forms two immiscible layers silicon tetrachloride White solid and steamy fumes (i) Write a balanced equation for the reaction of SiCl4 with water. [1] SiCl4(l) + 2H2O(l) → SiO2(s) + 4HCl (aq) (State symbols not required) (ii) CCl4 has no reaction with water. Suggest an explanation for the inertness of CCl4 to water.