ACJC_H2_CHEM_P3 Ans Prelim

1 © ACJC 2017 9729/03/Prelim/2017 [Turn over ANGLO-CHINESE JUNIOR COLLEGE DEPARTMENT OF CHEMISTRY Preliminary Examination CHEMISTRY 9729/03 Higher 2 Paper 3 18 August 2017 2 hours Additional Materials: Writing Paper Data Booklet Cover Page READ THESE INSTRUCTIONS FIRST Write your index number and name, form class and tutorial class on all the work you hand in. Write in dark blue or black pen. You may use a pencil for any diagrams, graphs or rough working. Do not use staples, paper clips, glue or correction fluid. Answer all questions in Section A. Answer either question 4 or 5 in Section B. Start each question on a new sheet of writing paper. A Data Booklet is provided. The use of an approved calculator is expected, where appropriate. You are reminded of the need for good English and clear presentation in your answers. At the end of the examination, fasten all your work securely behind a cover sheet. The number of marks is given in brackets [ ] at the end of each question or part question. This document consists of 17 printed pages, including this cover page. 9729/03/Prelim/17 ANGLO-CHINESE JUNIOR COLLEGE

2 © ACJC 2017 9729/03/Prelim/2017 [Turn over Section A – Answer ALL questions. Begin each question on a fresh piece of writing paper. 1 This question is about Period 3 and Group 2 elements. (a) Phosphorus sulfide, P4S3, is used in smal l amounts in the tip of a matchstick. On striking a match stick, this compound burns to form sulfur dioxide and phosphorus pentoxide. (i) Write the equation for this reaction. P4S3 + 8O2  3SO2 + P4O10 [1] (ii) The melting points of the two oxides formed in (a)(i) differ significantly from that of silicon(IV) oxide (SiO 2). Account for this difference in terms of structure and bonding of each oxide. The two above -mentioned oxides are simple covalent molecules while SiO2 has a giant covalent structure. Overcoming we ak IMF between P4O10 and SO2 molecules versus strong covalent bonds between Si and O atoms. SiO2 has the highest melting point. [2] (iii) The solid oxide formed in (a)(i) dissolves in water to give an acidic solution. Write the equation for this reactio n and give an appro