NJC Prelim CHEM P2

NJC Preliminary Examination 9647/02/15 NATIONAL JUNIOR COLLEGE SH2 PRELIMINARY EXAMINATION Higher 2 CANDIDATE NAME SUBJECT CLASS REGISTRATION NUMBER CHEMISTRY Paper 2 Structured Questions Candidates answer on the Question Paper. Additional Materials: Data Booklet 9647/02 Friday 28 August 2015 2 hours READ THESE INSTRUCTIONS FIRST Write your subject class, registration number and name on all the work you hand in. Write in dark blue or black pen. You may use a soft pencil for any diagrams, graphs or rough working. Do not use paper clips, highlighters, glue or correction fluid/tape. Answers all questions. A Data Booklet is provided. The number of marks is given in brackets [ ] at the end of each question or part question. For Examiner’s Use 1 /12 2 /12 3 / 7 4 /15 5 / 8 6 /13 7 / 5 Total /72 This document consists of 20 printed pages

2 NJC Preliminary Examination 9647/02/15 For Examiner’s Use Answer all the questions 1 Planning (P) The label on a bottle in your school chemistry laboratory is found to be missing and you are to help identify the organic compound in the bottle. The compound in the bottle is one of the following:  ethanal  propanamide  1-iodopentan-2-one  benzaldehyde  phenylamine (a) Plan a series of simple chemical tests that would allow you to confirm the identity of the compound in the bottle through a positive test. You are reminded that most of the compounds listed are flammable liquids. Your plan must include the following: ‐ the reagents and conditions to be used, but not the quantities of reagent used. ‐ observation(s) for each test. [6]

3 NJC Preliminary Examination 9647/02/15 [Turn over For Examiner’s Use (b) Assuming the unknown compound to be ethanal, it can react with 2,4-dinitrophenylhydrazine (2,4-DNPH) to fo rm a crystalline solid derivative (melting point 165 C). (i) Draw the displayed formula of the derivative formed between ethanal and 2,4-DNPH. [1] (ii) Write a plan for the preparation of the 2,4-DNPH derivative of ethanal. In your plan you should: − give a full description of the procedure you would use to prepare and purify the derivative; − explain how you would check the purity of your sample. …………….……………………………………………………………………………………… …………….……………………………………………………………………………………… …………….……………………………………………………………………………………… …………….……………………………………………………………………………………… …………….……………………………………………………………………………………… …………….……………………………………………………………………………………… …………….……………………………………………………………………………………… …………….……………………………………………………………………………………… …………….……………………………………………………………………………………… …………….……………………………………………………………………………………… …………….……………………………………………………………………………………… …………….……………………………………………………………………………………… …………….……………………………………………………………………………………… ...………………………………………………………………………………………………. [4] (c) Identify one potential safety hazard and state how you would minimise this risk. …………….……………………………………………………………………………………… ...………………………………………………………………………………………………. [1] [Total: 12]

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5 NJC Preliminary Examination 9647/02/15 [Turn over For Examiner’s Use (b) The van der Waals’ equation as shown below is often used to account for the discrepancies between experimental and theoretical behaviour of real gases. (p + 2 2 V an )(V – nb) = nRT where p is the pressure, V is the volume, T is the temperature, n is the amount of substance (in mol), and R is the gas constant. The van der Waals’ constants a and b are characteristic of the substance and are independent of temperature. (i) Given that the van der Waals’ constants a and b for SO2 are 0.687 Pa m 6 mol–2 and 5.68  10–5 m3 mol–1 respectively, calculate the pressure exerted by 1 mol of SO2 in a 0.50 dm3 container at 25 oC. [1] (ii) Calculate the pressure exerted by SO 2 as described in (b)(i) if it obeys the ideal gas law. [1] (iii) Suggest a reason for the discrepancy in the pressures obtained in (b)(i) and (b)(ii). ...…………………………………………………………………………………………... …...………………………………………………………………………………………... ……..…………………………………………………………………………………… [1]

6 NJC Preliminary Examination 9647/02/15 For Examiner’s Use (c) The type of bonding (covalent, ionic or me tallic) present in a substance can be determined and predicted using the van Arkel triangle based on the values of electronegativity of the element. Difference in electronegativity between the element(s) is plotted along the y–axis and the average electronegativity of the element(s) is plotted along the x–axis. The electronegativity data for oxygen and germanium, Ge, and some selected elements from Period 3 of the Periodic Table are given below. element electronegativity Na 0.93 Al 1.61 Si 1.90 Ge 2.01 S 2.58 Cl 3.16 O 3.61 In addition, some of the Period 3 elements and their compounds have been plotted on the van Arkel triangle given below. average electronegativity

7 NJC Preliminary Examination 9647/02/15 [Turn over For Examiner’s Use (i) Using your knowledge of the Period 3 elements and their compounds plotted on page 6, state the type of bonding present at each of these bonding extremes, labelled as A, B and C, on the triangle. A: ………………………… B: ………………………… C: ………………………… [2] (ii) I On the van Arkel triangle of page 6, plot the point corresponding to the oxide of germanium. Use this point together with your knowledge of the properties of Period 3 elements and their compounds, decide whet her the oxide of germanium is best described as an/a acidic, basic or amphoteric oxide. Nature of germanium oxide: ………………………… [2] II Hence explain if the melting point of the oxide of germanium would be lower or higher than that of the oxide of silicon. ……...…………………………………………………………………………….….. ………...………………………………………………………………………….….. …………...………………………………………………………………………... [2] [Tot