2025 TKGS Chemistry Prelim Paper 2 QP

TANJONG KATONG GIRLS’ SCHOOL PRELIMINARY EXAMINATION SECONDARY FOUR EXPRESS CHEMISTRY CANDIDATE NAME CLASS 4 INDEX NUMBER CHEMISTRY 6092/02 Paper 2 15 August 2025 1 hour 45 minutes Candidates answer on the Question Paper. No Additional Materials are required. 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. DO NOT WRITE ON ANY BARCODES. Section A Answer all questions. Write your answers in the spaces provided. Section B 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 24. The use of an approved scientific calculator is expected, where appropriate. For Examiner’s Use Section A Section B Total / 80 This document consists of 24 printed pages.

2 Tanjong Katong Girls’ School Sec 4 Preliminary Examination 2025 Section A Answer all questions. 1 The electron arrangement in the outer shells of five elements, A, B, C, D and E are shown in Fig.1.1. All elements are from Period 3 of the Periodic Table. Fig. 1.1 Use the letters A, B, C, D and E to answer the following questions. Each letter may be used once, more than once or not at all. (a) Which two elements are most likely to be metals? ………………………….. and ……………………….... [1] (b) Which element has an atomic number of 16? …………………………………………………………………………………………[1] (c) Which element will form double covalent bonds with an oxygen atom? …………………………………………………………………………………………[1] (d) Which two elements will form an ionic compound with the formula type XY? …………………………………………. and ………………………………………..[1] (e) Which element will form an oxide that reacts with both acids and bases? …………………………………………………………………………………………[1] [Total: 5]

3 Tanjong Katong Girls’ School Sec 4 Preliminary Examination 2025 2 (a) Table 2.1 shows information of atoms. Complete Table 2.1. Table 2.1 atoms number of protons number of neutrons number of electrons K19 39 28 24 [2] (b) The strength of interactions between particles determines whether the substance is a solid, liquid or gas at room temperature. Potassium oxide, K2O, is a solid while sulfur trioxide, SO3, is a liquid at room temperature. (i) Explain in terms of structure and bonding, why potassium oxide is a solid while sulfur trioxide is a liquid at room temperature. …………………………………………………………………………………...... …………………………………………………………………………………...... …………………………………………………………………………………...... …………………………………………………………………………………...... …………………………………………………………………………………..[3] (ii) State one other difference in the physical properties of potassium oxide and sulfur trioxide. …………………………………………………………………………………...... …………………………………………………………………………………..[1]

4 Tanjong Katong Girls’ School Sec 4 Preliminary Examination 2025 (iii) Draw a ‘dot-and-cross’ diagram to show the bonding in K2O. Show all outer shell electrons. [2] (c) Potassium oxide, aluminium oxide and sulfur trioxide are each added to separate samples of dilute sulfuric acid and aqueous sodium hydroxide. Complete Table 2.2 to show whether a reaction occurs in each case. Put a tick (✓) in the box if a reaction occurs. Table 2.2 dilute sulfuric acid dilute sodium hydroxide potassium oxide aluminium oxide sulfur trioxide [2] [Total: 10]

5 Tanjong Katong Girls’ School Sec 4 Preliminary Examination 2025 3 A student performs three experiments. In the first experiment, she adds large pieces of copper(II) carbonate to dilute hydrochloric acid. Copper(II) carbonate added is in excess. (a) Fig. 3.1 shows how the mass of the reaction mixture changes with time as the reaction proceeds. Fig. 3.1 (i) In the second experiment, powdered copper(II) carbonate is used instead of large pieces of copper(II) carbonate. All other conditions and the mass of copper(II) carbonate stay the same. Draw a line on the grid in Fig. 3.1 to show how the mass of the reaction mixture changes with time when powdered copper(II) carbonate is used. [1] time / min mass of reaction mixture /g

6 Tanjong Katong Girls’ School Sec 4 Preliminary Examination 2025 (ii) In the third experiment, the student uses large pieces of copper(II) carbonate and hydrochloric acid of a higher concentration. All other conditions stay the same. Describe and explain the difference in the rate of reaction when hydrochloric acid of a higher concentration is used. …………………………………………………………………………………...... …………………………………………………………………………………...... …………………………………………………………………………………..[2] (b) After the copper( II) carbonate has reacted completely with hydrochloric acid, the student places a clean strip of zinc metal into the resulting solution. Suggest and explain the observations. …………………………………………………………………………………………… …………………………………………………………………………………………… ………………………………………………………………………………………...[2] (c) Describe what you see when: (i) a few drops of aqueous ammonia are added to an aqueous solution containing copper(II) ions. …………………………………………………………………………………..[1] (ii) excess aqueous ammonia is added to an aqueous solution containing copper(II) ions. …………………………………………………………………………………..[1] (d) Describe how to prepare crystals of ammonium chloride by reacting aqueous ammonia with dilute hydrochloric acid. …………………………………………………………………………………………… …………………………………………………………………………………………… …………………………………………………………………………………………… …………………………………………………………………………………………… …………………………………………………………………………………………[3] [Total: 10]

7 Tanjong Katong Girls’ School Sec 4 Preliminary Examination 2025 4 (a) Petrol is a mixture of hydrocarbons that includes octane, C8H18. (i) Write an equation for the complete combustion of octane. …………………………………………………………………………………..[1] (ii) Suggest a reason why the fuel in an internal combustion engine is unlikely to undergo complete combustion. …………………………………………………………………………………..[1] (b) Exhaust gases from petrol engines contain compounds which are harmful to the environment. These includes oxides of carbon and nitrogen. (i) Write an equation to show the removal of carbon monoxide and nitrogen monoxide from the exhaust gases. …………………………………………………………………………………..[1] (ii) Thiophene, C4H4S, is present in crude oil fractions. During combustion, it produces sulfur dioxide. Combustion of fuels also produces nitrogen dioxide. Explain the effects of sulfur dioxide and nitrogen dioxide being released into the atmosphere. …………………………………………………………………………………….. …………………………………………………………………………………….. …………………………………………………………………………………….. …………………………………………………………………………………….. …………………………………………………………………………………..[2] (c) Explain, in terms of specific processes, how the carbon cycle regulates the amount of carbon dioxide in the atmosphere. …………………………………………………………………………………………… ………………………………………………………………………………………...[1] [Total: 6]

8 Tanjong Katong Girls’ School Sec 4 Preliminary Examination