2024 Prelims TJC H2 Chem P3 (Ans)

9729 / TJC Prelims / 2024 DO NOT WRITE IN THIS MARGIN [Turn over TEMASEK JUNIOR COLLEGE 2024 JC2 PRELIMINARY EXAMINATION Higher 2 CANDIDATE NAME CENTRE NUMBER S INDEX NUMBER Chemistry 9729/03 Paper 3 Free Response Questions 11 September 2024 2 hours Candidates answer on the Question Paper. Additional Materials: Data Booklet READ THESE INSTRUCTIONS FIRST Write your Centre number, index number and name 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. If additional space is required, you should use the pages at the end of this booklet. The question number must be clearly shown. Section A Answer all questions. Section B Answer one question. A Data Booklet is provided. The use of an approved scientific calculator is expected, where appropriate. 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 23 printed pages and 1 blank page. For Examiner’s Use Paper 3 Q1 /18 Q2 /20 Q3 /22 Q4 /20 Q5 /20 Total /80

2 DO NOT WRITE IN THIS MARGIN 9729 / TJC Prelims / 2024 DO NOT WRITE IN THIS MARGIN DO NOT WRITE IN THIS MARGIN DO NOT WRITE IN THIS MARGIN Section A Answer all the questions in this section. 1 (a) In Periodic Table, Group 14 consists of 5 elements. The elements at the top of the group, carbon to germanium, have very different properties from those at the bottom, tin and lead. For instance , carbon to germanium tend to adopt oxidation states of +4, whereas the heavier elements, such as tin and lead, exhibit the +2 oxidation state due to the inert pair effect. (i) Table 1.1 shows the melting points of the elements of Group 14. Table 1.1 element C Si Ge Sn Pb melting point / C >3550 1410 937 232 327 Carbon, silicon and germanium each forms a solid with the same type of structure. Using structure and bonding and the information from the Data Booklet, suggest why the melting points of these elements decrease from carbon to germanium. Carbon, silicon and germanium have √ giant molecular structure. Melting involves breaking √ numerous strong covalent bonds between atoms. Atomic radius nm C 0.077 Si 0.117 Ge 0.122 √ The atomic radius increases from C to Ge, leading to less effective overlap of the orbitals. √Bond strength decreases and hence less energy is required for melting. 2 √ : 1 mark [2] Carbon forms many allotropes such as graphite and diamond . Recent scientific research has found that replacing the graphite electrodes with graphene in lithium-ion batteries can extend battery life. Graphene is a si