SAJC Prelim P3_MS

1 [Turn over NAME Class ST ANDREW’S JUNIOR COLLEGE JC2 PRELIMINARY EXAMINATION Chemistry (9729) Paper 3 Free Response 15 September 2017 2 hours Additional Materials: Data Booklet, Writing Paper READ THESE INSTRUCTIONS: 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 questions. Marks [60] Section B Answer one question. Marks [20] 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. This document consists of XX printed pages (including this page).

2 [Turn over Section A Answer all the questions in this section. 1 (a) Iodine is a lustrous purple-black solid at standard conditions that sublimes readily to form a violet gas. (i) Give the equation that represents the second ionisation energy of iodine. [1] I+(g) I 2+ (g) + e [1] H>0 is not required since this is not a definition question. (ii) The graph below shows the second ionisation energies of eight elements with consecutive atomic number. Which of the above elements, A to H, is iodine? Explain your answer. [2] Element E. [1] The sharp drop from G to H indicates that G is from Group 1 where the second ionisation energy involves the removal of an electron from the inner principal quantum shell, which is nearer to the nucleus, requiring more energy. [1] Hence Element E is in Group 17 and is iodine. (iii) Explain the trend in second ioni sation energies from elements A to G, including the irregularity for element B. [4] A B C D E F G H Second Ionisation energy/ kJ mol-1 Proton number

3 [Turn over The second IE generally increases from A to G because from A to G, there is an increase in proton number and hence nuclear charge while shielding effect is almost constant as electrons are added to the same quantum shell. [1] Hence effective nuclear charge increases and the attraction for the outermost electron becomes increasingly stronger. [1] More and more energy is required to remove the strongly attracted valence electron as we move across the period. Second IE of B is lower than that of A because the electron is removed from the valence 5p subshell which is further away from the nucleus compared to the 5s subshell in A. [1] It also experiences additional screening effect by the two 5s. These factors outweigh the effect of increase in nuclear charge from A to B, resulting in a weaker attraction by the nucleus.[1] Less energy is required to remove the outermost electron in B than that in A. (iv) Suggest, with reason, which of the above elements, A to H, can form an amphoteric oxide. Hence, write an equation to show the