2024 CGS Chemistry Prelim P2_Mark Scheme

Page 1 of 22 CRESCENT GIRLS’ SCHOOL SECONDARY FOUR PRELIMINARY EXAMINATION 2024 Paper 2 READ THESE INSTRUCTIONS FIRST Candidates answer on the Question Paper. No Additional Materials are required. Write your name, index number and class in the spaces provided at the top of this page. Write in dark blue or black pen. You may use an HB pencil for any diagrams or graph. Do not use staples, paper clips, and glue or correction fluid. Section A (70 Marks) Answer all questions Write your answers in the spaces provided Answer one question. Write your answers in the spaces provided. Answer one question. Write your answers in the spaces provided. The number of marks is given in brackets [ ] at the end of each question or part question. A copy of the Periodic Table is printed on page 23. The use of an approved scientific calculator is expected, where appropriate. For Examiner’s Use Section A Section B Deductions Significant Figures Units Total 80 This paper consists of 22 printed pages including the cover page. CHEMISTRY Class: Register No: Name: 6092/02 23 August 2024 1 hr 45 mins

Page 2 of 22 Section A Answer all questions in this section in the spaces provided. The total mark for this section is 70. A1 The figure below shows ‘dot-and-cross’ diagrams for molecules that contain elements from the first two periods of the Periodic Table. The elements are represented by the letters M, Q, R, T and Z. Each diagram shows outer electrons only. Use the letters M, Q, R, T and Z to answer the questions below. (a) Which element can form an ion with a charge of 1-? [1] Q or Z (b) Which element can gain, lose and share electrons? [1] Z (c) Which element can form an acidic oxide? [1] M or Q or R (d) Which element forms a triple covalent bond? [1] M

Page 3 of 22 (e) (i) Potassium reacts with element T to form a compound. Draw a dot-and-cross diagram of the compound formed between potassium and element T. Show only the valence electrons. [2] Correct charge – [1], correct ratio – [1] (ii) State one physical property of the above compound and explain the reason for the physical property. [2] High mp/bp (✓) – strong electrostatic FOA between oppositely charged ions (✓) and hence large amount of energy (✓) to overcome. OR Good electrical conductor (✓) in aqueous/molten (✓) state – ions are mobile (✓) to conduct electricity OR Poor electrical conductor (✓) in solid (✓) state – ions are in fixed positions (✓) and cannot conduct electricity 3 (✓) – [2], 1 – 2 (✓) – [1] Allow ecf if the properties match the dot and cross diagram [Total: 8 marks] K T

Page 4 of 22 A2 The table below shows info