CGSS 2023 Chemistry Prelim Paper 2A

CEDAR GIRLS’ SECONDARY SCHOOL Preliminary Examination 2023 Secondary Four CANDIDATE NAME CLASS 4 INDEX NUMBER CHEMISTRY 6092/2 Paper 2 Section A 29 August 2023 1 hour 45 minutes Additional Materials: NIL For Examiner’s Use Section A 1 5 2 11 3 7 4 12 5 7 6 8 Total 50 This document consists of 23 printed pages and 1 blank page. [Turn over READ THESE INSTRUCTIONS FIRST Write your name and index number on all the work you hand in. You may use a pencil for any diagrams, graphs or rough working. Do not use paper clips, highlighters, glue or correction fluid. Section A Answer all questions. Write your answers in the spaces provided on the question paper. Section B Answer all three questions. The last question is in the form either/or. Write your answers in the spaces provided on the question paper. A copy of the Periodic Table is printed on page 24. At the end of the examination, hand in your answers to Section A and Section B separately.

2 For Examiner's Use Section A Answer all questions in this section in the spaces provided. The total mark for this section is 50. A1 Choose from the following chlorides to answer the questions. aluminium chloride ammonium chloride calcium chloride hydrogen chloride silver chloride sodium chloride Each chloride may be used once, more than once or not at all. Which chloride (a) contains a cation with a +2 charge ………………………………………..……………………………………………… [1] (b) reacts with warm aqueous sodium hydroxide to form a gas which turns damp red litmus paper blue ………………………………………..……………………………………………… [1] (c) has a molecule which only has 18 protons ………………………………………..……………………………………………… [1] (d) forms a white precipitate in aqueous ammonia ………………………………………..……………………………………………… [1] (e) is soluble in organic solvents? ………………………………………..……………………………………………… [1] [Total:5]

3 [Turn over For Examiner's Use A2 Hydrogen is used as an alternative energy source as it is a clean fuel. The process of making hydrogen has several stages. The equations show two stages in the process. Stage 1: CH4(g) + H2O(g) ⇌ CO(g) + 3H2(g) Stage 2: CO(g) + H2O(g) ⇌ CO2(g) + H2(g) (a) Both stages require the use of catalyst s to increase the rate of reaction. Catalysts are expensive to buy but reduce costs in the long run. (i) Explain, in terms of collisions and energy, why using a catalyst increases the rate of reaction. ………………………………………………………………………………….. ………………………………………………………………………………….. ………………………………………………………………………………….. ………………………………………………………………………………….. ………………………………………………………………………………….. [2] (ii) Give two reasons to explain why catalysts reduce costs in the long run. ………………………………………………………………………………….. ………………………………………………………………………………….. ………………………………………………………………………………….. ………………………………………………………………………………….. [2] (b) The forward reaction in Stage 2 has a benefit to human health. Use the equation in Stage 2 to explain the benefit of this stage. ……………………………………………………………………………………….. ……………………………………………………………………………………….. ……………………………………………………………………………………….. [2] (c) Deduce the change in oxidation state of hydrogen in Stage 2. ……………………………………………………………………………………….. [1]

4 For Examiner's Use (d) Explain with the aid of a chemical equation, why hydrogen is considered a ‘clean fuel’. ……………………………………………………………………………………….. ……………………………………………………………………………………….. ……………………………………………………………………………………….. [2] (e) The enthalpy change when 1 mole of hydrogen is completely burned is −286 kJ/mol. Calculate the enthalpy change when 1 kg of hydrogen is completely burned in kJ/kg. [2] [Total: 11]

5 [Turn over For Examiner's Use A3 Iodine can be extracted from natural sources through a variety of methods. The flowchart in Fig. 3.1 summarises one such method. Fig. 3.1 (a) In Process 1, aqueous sodium iodide was reacted with aqueous silver nitrate. Write an ionic equation for this reaction. ……………………………………………………………………………………….. [2] (b) Processes 2 and 3 occur via displacement reactions. Explain the reactions that occur in each process. Identify Product A and B in your answer. ……………………………………………………………………………………….. ……………………………………………………………………………………….. ……………………………………………………………………………………….. ……………………………………………………………………………………….. ……………………………………………………………………………………….. ……………………………………………………………………………………….. [4] (c) Solid iodine collected in Step 3 was found to be impure. State a method to obtain a pure sample of solid iodine. ……………………………………………………………………………………….. [1] [Total: 7]

6 For Examiner's Use A4 The first chemical source of current electricity was the voltaic pile . It consists of a stack of alternating copper and zinc discs, with a moistened cloth soaked in an aqueous electrolyte placed on top of each copper disc. Fig. 4.1 shows a voltaic pile. The electrolyte is made up of aqueous copper(II) ions and zinc ions. Fig. 4.1 (a) Complete Table 4.1. Table 4.1 metal positive or negative electrode cathode anode [2] (b) When a current is drawn for some time, changes take place for the metal discs. Describe and explain how the mass of copper and zinc discs will change. ………………………………………..……………………………………………… ………………………………………..……………………………………………… ………………………………………..……………………………………………… ………………………………………..……………………………………………… ………………………………………..……………………………………………… ………………………………………..……………………………………………… [3]

7 [Turn over For Examiner's Use (c) Explain why a higher voltage was produced when a combination of silver and zinc discs were used instead. ……………………………………………………………………………………….. ……………………………………………………………………………………….. [1] (d) The electrolysis of concentrated hydrochloric acid was conducted using platinum electrodes as shown in Fig. 4.2. Fig. 4.2 (i) Give half-equations for the reaction at each electrode. positive electrode …………………………………………………………… negative electrode ……………………………..…………………………… [2] (ii) Using your answer in (d)(i), explain if the expected volume of gases collected at the gas syringe will be the same or different. ………………………………………………………………………………… ………………………………………………………………………………… ………………………………………………………………………………… [1] (iii) In the actual experiment, the volume of gas collected in gas syringe X was always less than that collected in gas syringe Y. Suggest why this was observed. ………………………………………………………………………………… ………………………………………………………………………………… [1]

8 For Examiner's Use (iv) The platinum electrodes were replaced with silver electrodes. A white precipitate was observed at one of the electrodes. Identify the white precipitate and explain why this was observed. ………………………………………………………………………………… ………………………………………………………………………………… ………………………………………………………………………………… ………………………………………………………………………………… [2] [Total: 12]

9 [Turn over For Examiner's Use A5 Malachite is an ore of copper. The formula of malachite is CuCO 3•Cu(OH)2. In this formula, one formula unit of copper(II) carbonate combines with one formula unit of copper(II) hydroxide. Malachite undergoes reactions in a similar manner as a mixture of copper(II) carbonate and copper(II) hydroxide. A small solid sample of malachite is added to excess dilute nitric acid. The carbon dioxide formed is collected and has a volume of 96 cm3 at room temperature and pressure.