Bowen 5105 Sci Chemistry Paper 4

Class Full Name Index Number PRELIMINARY EXAMINATION 2023 I believe, therefore I am SCIENCE (CHEMISTRY) Paper 4 Secondary 4 Normal Academic Papers 3 and 4: 1 hour 15 minutes Candidates answer on the Question Paper No Additional Materials are required. 28 July 2023 READ THESE INSTRUCTIONS FIRST Write your name, class and index number on all the work you hand in. Write in dark blue or black pen on both sides of the writing paper. You may use an HB pencil for any diagrams or graphs. Do not use staples, paper clips, glue or correction fluid. Answer all questions in Section A and any two questions in Section B. The use of an approved scientific calculator is expected, where appropriate. In calculations, you should s how all the steps in your working, giving your answer at each stage. You are advised to spend no longer than 30 minutes on Paper 3. You may proceed to answer Paper 4 as soon as you have completed Paper 3. A copy of the Periodic Table is printed on page 12. At the end of the examination hand in your a nswers to Paper 3 and Paper 4 separately. Enter the numbers of Section B questions you have answered on the dotted line in the grid below. The numb er of marks is given in brackets [ ] at the end of each q uestion or part question. DO NOT OPEN THIS PAPER UNTIL YOU ARE TOLD TO DO SO For Examiner’s Use Section A Section B ………..... ………….. Total This document consists of 12 printed pages, including the cover page. 30 N 5105/5107/04

2 [Turn over Section A Answer all the questions in the spaces provided. A1 The diagrams below represent the particles of six different substances at room temperature and pressure. Complete the table below to show which diagrams, A to F, best represent each of the following descriptions. You may use each letter once, more than once or not at all. Substance Diagram (a) Water (b) Oxygen gas (c) Mercury (d) Mixture [4] [Total:4] For Examiner’s Use

3 [Turn over A2 In Singapore, it is an offence for the driver of a motor vehicle to leave the engine of a vehicle idlin g while it is s tationary. This measure is implemented to control the emissions generated by motor vehicles and safeguard public health. Nitrogen monoxide and carbon monoxide are the most polluting emissions from vehicle combustion engines. The concentration of each of these components depends on the mode of operation and the air-fuel ratio of the vehicle. The table below shows some information on these pollutants. scenario mode of operation air-fuel ratio concentration of NO/ppm concentration of CO/ppm 1 idling engine 12:1 10 8500 2 idling engine 15:1 14 4500 3 accelerating 12:1 1000 5000 4 accelerating 15:1 3700 1000 (a) Using the information from the table, (i) state the relationship between the air -fuel ratio and the concentration of CO emitted. ………………………………………………………………………………………………. ……………………………………………………………………………………………. [1] (ii) suggest why the concentration of NO is higher in accelerating mode, which has higher temperature, as compared to idling mode. ………………………………………………………………………………………………. ……………………………………………………………………………………………. [1] (b) Name the type of chemical reaction that occurs when fuels are burnt in limited supply of air. ……………………………………………………………………………………………. [1] (c) Briefly describe how NO and CO can affect the public health. ………………………………………………………………………………………………. ………………………………………………………………………………………………. ……………………………………………………………………………………………. [2] [Total: 5] For Examiner’s Use

4 [Turn over A3 The diagram below shows how an organic compound pentadecane, C 15H32, breaks down in the presence of aluminium oxide. (a) Name the process shown in the diagram. …………………………………………………………………………………………….. [1] (b) 5.30g of pentadecane was used for the process. Calculate the amount, i n moles, of pentadecane used. [relative atomic masses Ar: C, 12; H, 1] amount of pentadecane = ………………….. mol [2] (c) The chemical equation for the process that occurs is given below. C15H32 → 2C2H4 + C3H6 + C8H18 Draw a ‘dot and cross’ diagram of one molecule of C2H4. Show only the outer-shell electrons. [2] [Total: 5] For Examiner’s Use Mineral wool soaked with pentadecane e aluminium oxide granules mixture of smaller hydrocarbons

5 [Turn over Section B Answer any two questions in the spaces provided. B4 The table below show s the reactions of alkali metals ( lithium, sodium and potassium ) with oxygen. metal reaction with oxygen lithium burns quickly with a red flame to give a white solid residue sodium burns very quickly with a bright yellow fl ame to give a white solid residue potassium burns violently with a lilac flame to give a white solid residue (a) Using M as the symbol to represent an alkali metal, write a general equation for the reaction between an alkali metal and oxygen. …………………………………………………………………………………………….. [1] (b) Using the information from the table, state the trend in the reactivity of the alkali metals towards oxygen. …………………………………………………………………………………………….. [1] (c) The reactivit y of the alkali metals towards water is similar to that of alkali me tals towards oxygen. Rubidium is placed below potassium in the Periodic Table. Suggest one possible observation when rubidium reacts with water. …………………………………………………………………………………………….. [1] (d) The relative atomic masses and the melting points of th e alkali metals are given below. metal relative atomic mass melting point/°C lithium 7 181 sodium 23 98 potassium 39 ? rubidium 85 39 (i) Plot a graph of melting point against relative atomic mass, marking each point with a cross (X). [1] (ii) Draw a curved line of best fit, taking into account all your plotted points. [1] For Examiner’s Use

6 [Turn over