SRJC_H1_CHEM_P2_ANS

1 SRJC 8872 / 02 / JC2 Prelims/ 2015 SERANGOON JUNIOR COLLEGE General Certificate of Education Advanced Level Higher 1 CANDIDATE NAME CLASS CHEMISTRY 8872/02 JC 2 Preliminary examination 20 August 2015 Paper 2 2 hours Additional Materials: Data Booklet READ THESE INSTRUCTIONS FIRST Candidates answer on the question paper. Write your name and class on all the work you hand in. Write in dark or blue pen. Do not use paper clips, glue or correction fluid. The number of marks is given in bracket [ ] at the end of each question or part question. At the end of the examination, fasten all your work securely together. This document consists of 13 printed pages and 3 blank page. FOR EXAMINER’S USE P1 (MCQ) 30 P2 A1 8 A2 9 A3 16 A4 7 B5 20 B6 20 B7 20 Total 110

2 SRJC 8872 / 02 / JC2 Prelims/ 2015 Section A Answer all the questions in the spaces provided. 1 Elements A, B, C, D and E are five consecutive elements from Period 3 and 4 of the Periodic Table. The following shows the successive ionisation energies of element C. No. of electrons removed 1 2 3 4 5 6 7 8 Ionisation energy / kJ mol–1 1260 2300 3850 5150 6542 9362 11018 33604 (a) (i) Deduce and explain which group element C belongs to. [2] Group VII. Largest jump in ionisation energy from 7 th to 8 th electron. Thus, there are 7 valence electrons. The 8th electron is located in an inner principal quantum shell nearer the nucleus, thus experience stronger electrostatic forces of attraction, requiring much more energy to remove. (ii) Hence, state the identity of element C and write down its electronic configuration. [2] Chlorine . Electronic configuration: 1s22s22p63s23p5. (b) Explain the following observations, giving equations where appropriate. (i) The first ionisation energy of element B is lower than the first ionisation energy of element A. [2] B is sulfur: [Ne]3s23p4, A is phosphorus: [Ne]3s23p3 In B, there is interelectronic repulsion between the pair of electrons in the doubly -filled 3p orbital of B . Less energy is required to overcome the weaker electrostatic forces of attraction between the nucleus and the paired valence 3 p electron in B compared to the unpaired valence 3p electron in A. (ii) A strongly acidic solution is formed when the chloride of A reacts with water. [2] Chloride of A undergoes hydrolysis to give white fumes of HCl gas PCl3 (l) + 3 H2O (l) → H3PO3 (aq) + 3 HCl (aq) Or PCl5 (l) + 4 H2O (l) → H3PO4 (aq) + 5 HCl (aq) pH of solution ≈ 2 [Total: 8] For Examiner’s use

3 SRJC 8872 / 02 / JC2 Prelims/ 2015 2 A sequence of reactions is shown below. (a) In the appropriate boxes draw the structures of compound F,