Serangoon Prelim P2

1 SERANGOON SECONDARY SCHOOL PRELIMINARY EXAMINATION SECONDARY 4 EXPRESS CANDIDATE NAME ( ) CLASS CENTER NUMBER S INDEX NUMBER CHEMISTRY 6092/02 Paper 2 22 Aug 2024 1 hour 45 minutes Candidates answer on the Question Paper. Setter(s): 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 staplers, paper clips, glue or correction fluid. 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 27. The use of an approved scientific calculator is expected, where appropriate. This question paper consists of 26 printed pages, including this cover page. For examiner’s use Section A 70 Section B 10 9 10 Total 80

2 Section A [70 marks] Answer all questions. 1 Fig. 1.1 shows part of the Periodic Table. Li C N O A l Ca Fe Cu Zn Fig. 1.1 Select elements from Fig. 1.1 to answer the following questions. You may use each element once, more than once or not at all. Write down the symbol for an element which: (a) forms a stable ion by losing three electrons, ………………………………………………………………………………………..….…... [1] (b) exists as diatomic molecules, ………………………………………………………………………………………..….…... [1] (c) forms an ion which gives a red-brown precipitate on addition of aqueous ammonia, ………………………………………………………………………………………..….…... [1] (d) has chemical properties similar to those of magnesium, ………………………………………………………………………………………..….…... [1] (e) has a giant covalent structure, ………………………………………………………………………………………..….…... [1] (f) reacts with sodium to form an ionic compound with Mr less than 70. ………………………………………………………………………………………..….…... [1] [Total: 6]

3 2 A laboratory technician mixes red, blue and yellow dyes to make black dye for a paper chromatography experiment. A common solvent used to separate the dyes in black ink is a mixture of ethanol and water. The coloured dyes have different Rf values in solvents with different composition of ethanol as shown in Fig. 2.1. Fig. 2.1 (a) Predict the colours of the separated spots observed when the solvent used consists of 40% ethanol in the mixture. ………………………………………………………………………………………..….….. [1] (b) State the Rf value of the yellow dye on the chromatogram when the solvent is a mixture of 64 cm3 of ethanol and 136 cm3 of water. ………………………………………………………………………………………..….….. [1] (c) Explain why a pure solvent of water or ethanol is not suitable for the separation of the black ink using paper chromatography. ………………………………………………………………………………………..………..….. ………………………………………………………………………………………..….………... ………………………………………………………………………………………..….….. [2] Rf value percentage of ethanol in solvent mixture/ %

4 (d) A student carried out chromatography on the black ink using a mixture of ethanol and water as solvent. Only one spot was observed on the resulting chromatogram. What is the percentage of ethanol in the solvent mixture used? Explain why only one spot is observed. ………………………………………………………………………………………..………..….. ………………………………………………………………………………………..….………... ………………………………………………………………………………………..….….. [2] (e) Draw and label on the chromatography paper below the chromatogram obtained when a mixture containing 90% ethanol is used. [1] [Total: 7]

5 3 Until recently, arsenic poisoning, either deliberate or accidental, has been a frequent cause of death. The symptoms of arsenic poisoning are identical to those of a common illness, cholera. A reliable test was needed to prove the presence of arsenic in a body. In 1840, Marsh devised a reliable test for arsenic as shown in Fig 3.1. Fig 3.1 Hydrogen is formed in this reaction. (a) Any arsenic compound reacts with this hydrogen will form arsine which is arsenic hydride, a covalent compound. The mixture of hydrogen and arsine is burnt at the jet and arsenic forms as a black stain on the glass. (i) Write an equation for the reaction which forms hydrogen. ………………………………………………………………………………………. [1] (ii) Arsenic (As) is located in Group 15. Suggest the formula of arsine. ………………………………………………………………………………………. [1] hydrochloric acid cold surface black stain shows presence of arsenic pieces of zinc and arsenic compound H2 and arsine burning

6 (iii) Draw a ‘dot and cross’ diagram to show the bonding in the compound arsine. Show the outer shell electrons only. [2] (b) Table 3.1 shows the composition of another hydride of arsenic. Table 3.1 arsenic hydrogen 97.4% 2.6% (i) Determine the empirical formula of this hydride from the data above. empirical formula: …………………… [2] (ii) The mass of one mole of this hydride is 154 g. What is its molecular formula? molecular formula: …………………… [1] (iii) Draw the full structural formula of this hydride from (b)(ii). [1] [Total: 8]

7 4 This question is about halogens and their compounds. (a) Explain in terms of electron transfer why halogens behave chemically as non- metals. ……………………………………………………………………………………………..….……. ………………………………………………………………………………………….……. [1] (b) Complete Table 4.1 to show the results of experiments where aqueous halogens are added to the solutions of aqueous halides. Use the following legend: a reaction occurs no reaction occurs Table 4.1 At 2 (aq) Br 2 (aq) Cl2 (aq) At – (aq) Br – (aq) Cl – (aq) [2] (c) Two students commented on the use of potassium iodide. Student 1: “Potassium iodide can be very useful because when it is oxidised, a colour change is produced.” Student 2: “Aqueous potassium iodide can be used to test for the presence of an oxidising agent.” (i) Describe the colour change when potassium iodide is oxidised. ……………………………………………………………………………………… [1] (ii) Explain why the reaction between aqueous potassium iodide and oxidising agents is a redox reaction. ………………………………………………………………………………..…………… ………………………………………………………………………………..…………… ……………………………………………………………………………………… [2]

8 (d) Concentrated aqueous hydrochloric acid releases fumes of hydrogen chloride gas. A long glass tube is set up as shown in Fig. 4.1. Fig. 4.1 Use the kinetic particle model to explain why the blue litmus paper turns red after a short while. ………………………………………………………….…………………………..……………… ………………………………………………………….…………………………..……………… ………………………………………………………….…………………………..……………… ………………………………………………………………………………..……………… [3] [Total: 9] 5 Ozone does not come directly from factories and vehicles. Ozone is formed when heat and sunlight cause chemical reactions between oxides of nitrogen (NOX) and Volatile Organic Compounds (VOC). This reaction can occur both near the ground and high in the atmosphere. (a) (i) Predict the effect of each factor on the ozone level by completing Table 5.1. Table 5.1 Factor Ozone levels (Increase or Decrease) Smaller population density More electrical cars Sunny skies [1] (ii) Ozone levels in a city are usually at their peak in mid-afternoon. Suggest two reasons for this. ……………………………………………………………………………………………….. ……………………………………………………………………………………………….. ………………………………………………………………………………………… [2] cotton wool soaked in concentrated hydrochloric acid damp blue litmus paper

9 (b) In