EJC 2020 JC2 Prelim H2 Chemistry Paper 2 Suggested Solutions

© EJC [Turn Over EUNOIA JUNIOR COLLEGE JC2 Preliminary Examination 2020 General Certificate of Education Advanced Level Higher 2 CANDIDATE NAME CIVICS GROUP 1 9 – INDEX NUMBER CHEMISTRY Paper 2 Structured Questions 9729/02 02 September 2020 2 hours Candidates answer on the Question Paper Additional Materials: Data Booklet READ THESE INSTRUCTIONS FIRST Write your name, civics group, index 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. Answer all questions in the spaces provided on the Question Paper. 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. For Examiner’s Use Paper 2 1 / 12 2 / 12 3 / 18 4 / 16 5 / 17 Total / 75 This document consists of 21 printed pages and 1 blank page.

2 © EJC 9729/02/J2PE/20 For Examiner’s Use 1 (a) Nitrogen can form a few hydrides such as NH3 and N2H4. The boiling points of these two hydrides are given in Table 1.1. Table 1.1 compound boiling point / ºC NH3 −33 N2H4 114 Provide two explanations for why N2H4 has a higher boiling point than NH3. ................................ ................................ ................................ ................................ .... ................................ ................................ ................................ ................................ .... ................................ ................................ ................................ ................................ .... ................................ ................................ ................................ ................................ .... ................................ ................................ ................................ ................................ .... ................................ ................................ ................................ ................................ .... ................................ ................................ ................................ ................................ .... ................................ ................................ ................................ ................................ .... ................................ ................................ ................................ ................................ [2] N2H4 can form an average of two hydrogen bonds per molecule while NH3 can only form one. More energy is required to break the more extensive hydrogen bonds between N 2H4, hence it has a higher boiling point. N 2H4 also has more electrons, which gives rise to a larger a