Copy of 2024 CCHM Chemistry 6092 P2

[Turn over Name: Class: Class Register Number: PRELIMINARY EXAMINATION 2024 SECONDARY 4 CHEMISTRY 6092/02 Paper 2 21 August 2024 1 hour 45 minutes Candidates answer on the Question Paper. No Additional Materials are required. READ THESE INSTRUCTIONS FIRST Write your name, class and register number clearly 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 graphs. Do not use staples, paper clips, glue or correction fluid. Section A Answer all questions 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 / 70 Section B / 10 Total / 80 This document consists of 23 printed pages and 1 blank page.

2 2024 Preliminary Exam/CCHMS/Secondary 4/Chemistry/6092/02 Section A Answer all questions. 1 The electronic structures of five atoms, A, B, C, D and E, are shown. A B C D E (a) Answer the following questions about these electronic structures. Each electronic structure may be used once, more than once or not at all. State which electronic structure, A, B, C, D or E represents: (i) an atom of an element in Group 2 of the Periodic Table ………………………...…………………………………………………………,……..[1] (ii) an atom of a very reactive metal …………………………………………………...…………………………………,…..[1] (iii) an atom with a proton number of 17 …………………………………………………...………………………………,……..[1] (iv) an atom that forms a stable ion with a charge of 2− ……………………………………………………...……………………………,……..[1] (b) Atoms B and C reacts to form a compound. Draw a ‘dot -and-cross’ diagram to show the bonding between atoms B and C. Show outer electrons only. [2] [Total: 6]

3 [Turn over 2024 Preliminary Exam/CCHMS/Secondary 4/Chemistry/6092/02 2 Silver dichromate, Ag2Cr2O7, is a red insoluble salt. Silver dichromate can be made by reacting silver nitrate solution with ammonium dichromate solution as shown by the equation below. 2AgNO3 + (NH4)2Cr2O7 → 2NH4NO3 + Ag2Cr2O7 (a) (i) Describe how you can obtain pure and dry solid silver dichromate after mixing silver nitrate solution and ammonium dichromate solution. ……………………………………………………………………………………………... ……………………………………………………………………………..…….……..[2] (ii) Describe the steps that you would take to determine if silver nitrate solution is present in the reaction mixture after the reaction stops. ………………………………………………………………………………………..….... ………………………………………………………………………………………..….... …………………………………………………………………………………………...... ………………………………………………………………………………………..…[3] (b) (i) Deduce the oxidation state of chromium in Ag2Cr2O7. ……………………………………………………………………………..…….……..[1] (ii) Write the ionic equation, with state symbols, for the formation of silver dichromate in this reaction. ……………………………………………………………………………...…….…..…[2] (c) The apparatus shown below is set up. After five minutes, a red solid appeared at the position marked S on the diagram. (i) Explain why a red solid appeared at the position marked S. ……………………………………………………………………………..……….……... …………………………………………………………………………………..…….…... ………………………………………………………………………………..….……..[2]

4 2024 Preliminary Exam/CCHMS/Secondary 4/Chemistry/6092/02 (ii) The experiment is then repeated at a higher temperature. What effect, if any, would this have on the time taken for the red solid to appear? Explain your answer. …………………………………………………………………………………..………… …………………………………………………………………………………………..[1] [Total: 11]

5 [Turn over 2024 Preliminary Exam/CCHMS/Secondary 4/Chemistry/6092/02 3 A student investigated the change in mass when hydrated cobalt chloride is heated. The chemical equation for the reaction is: CoCl2•6H2O → CoCl2 + 6H2O This is the method used. 1. Add 2.0 g of hydrated cobalt chloride to an empty test tube. 2. Measure the mass of the test tube and contents. 3. Heat the test tube and contents gently for 30 seconds. 4. Allow the test tube and contents to cool. 5. Measure the mass of the test tube and its contents. 6. Repeat steps 3 to 5 until the mass of the test tube and its contents do not change. (a) Predict if the mass of the test tube and its contents increase or decrease after heating. Give a reason for your answer. ……………………………………………………………………………………………............... ……………………………………………………………………………………………...........[1] (b) Suggest why the test tube and its contents were heated until the mass did not change. ……………………………………………………………………………………………….......[1] (c) (i) When 238 g of hydrated cobalt chloride is heated until the mass does not change, 88.1 kJ of energy is taken in. Calculate the energy taken in when the student heated 2.00 g of hydrated cobalt chloride until the mass did not change. Energy taken in = ………………………..kJ [2]

6 2024 Preliminary Exam/CCHMS/Secondary 4/Chemistry/6092/02 (ii) Complete the energy profile diagram for the decomposition of hydrated cobalt chloride. Your diagram should show: • chemical formula of the products of the reaction, • labels to show the activation energy and enthalpy change of the reaction. [3] [Total: 7] energy CoCl2•6H2O progress of reaction

7 [Turn over 2024 Preliminary Exam/CCHMS/Secondary 4/Chemistry/6092/02 4 The diagram shows a Group in a Periodic Table designed by John Newlands in 1864. The Group contains elements found in Group 17 (the halogens) of the modern Periodic Table and other elements. H F Cl Co/Ni Br Pd I Pt/Ir (a) Use the modern Periodic Table to suggest why Newlands put cobalt and nickel in the same place. …………………….…………………………………………………………………..…….…...[1] (b) Cobalt, nickel, palladium, platinum and iridium are now classified as transition elements. State two ways in which the properties of transition elements are different from halogens. ………………………………………………………………………………………….................. …………………………………………………………………………………………….............. …………………………………………………………………………………………….............. …………………………………………………………………………………………….…......[2] (c) Hydrogen is difficult to be placed in the modern Periodic Table. (i) State one way in which hydrogen is similar to the elements in Group 1. …………………………………………………………………………………….…......... ………………………………………………………………………………………......[1] (ii) State one property of hydrogen which makes it similar to the elements in Group 17. …………………………………………………………………………………….…......... …………………………………………………………………………………………...[1] [Total: 5]

8 2024 Preliminary Exam/CCHMS/Secondary 4/Chemistry/6092/02 5 A car manufacturer is planning to sell hybrid cars powered by a type of hydrogen fuel cell that uses acid electrolyte. A representation of the hydrogen fuel cell is given below. The overall cell reaction is 2H2(g) + O2(g) → 2H2O(g) (a) State if oxidation or reduction has occurred at electrode A. Explain your answer. ………….………….………………………….………………………………………………...[1] (b) Identify product C. …………………….…………………………………………….………………….…………...[1] (c) Write an equation for the reaction that occurs at electrode B when the switch is closed. ……………………………………………………………………………………………...…...[1] (d) Identify one advantage and one disadvantage of using this fuel cell instead of a petrol engine to power the car. advantage………………………………………………..……………………………