Copy of 2024 SCGS Chemistry Prelim P2 answers

CANDIDATE NAME CLASS 4 REGISTER NUMBER CENTRE NUMBER INDEX NUMBER CHEMISTRY Paper 2 Theory 6092/02 20 August 2024 1 hour 45 minutes READ THESE INSTRUCTIONS FIRST Write your class, index number and name on all the work you hand in. Write in dark blue or black pen. You may use a HB pencil for any diagrams or graphs. Do not use staples, paper clips, highlighters, glue or correction fluid/tape. Section A Answer all questions. Write your answers in the spaces provided. Section B Answer one question. Answer all questions 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 20. The use of an approved scientific calculator is expected, where appropriate. This question paper consists of 20 printed pages. SINGAPORE CHINESE GIRLS’ SCHOOL Preliminary Examination Secondary Four For Examiner’s Use Section A 70 Section B 10 Total 80

2 [Turn over] Section A Answer all questions 1 These diagrams show the electron arrangement in the outer shells of five elements, A to E. All elements are from Period 3 of the Periodic Table. Use the letters A to E to answer the following questions. You may use each letter once, more than once or not at all. (a) Which elements are most likely to be non-metals? ………………………………………………………………………………………………………. [1] (b) Which elements can act as reducing agents? ………………………………………………………………………………………………………. [1] (c) Which element has an atomic number of 16? ………………………………………………………………………………………………………. [1] (d) Which element will form three covalent bonds when it forms compounds? ………………………………………………………………………………………………………. [1] (e) Which two elements will form a compound with the formula of the type YZ 2? ………………………………………………………………………………………………………. [1] (f) Which element will form an oxide that reacts with both acids and bases? ………………………………………………………………………………………………………. [1] [Total: 6] A, B, E C, D A E D and B / A and B C

3 [Turn over] 2 Ethylamine, CH3CH2NH2, behaves similarly to ammonia in terms of its chemical properties. The equation below shows what happens when ethylamine is dissolved in water. CH3CH2NH2 + H2O ⇌ CH3CH2NH3+ + OH– (a) According to the Br Ønsted-Lowry theory, an acid is defined as a species that can donate protons (H+), while a base is a species that can accept protons. Based on the Br Ønsted-Lowry theory and the given equation, explain whether ethylamine acts as an acid or a base. ………………………………………………………………………………………………………….. ……………………………………………………………………………………………………….[1] (b) The pH scale is a method to measure the acidity or alkalinity of a substance. Predict the pH of an aqueous solution of ethylamine. …………………………………………………………………………………………………….…[1] (c) Explain, in terms of structure and bonding, why