SJI 2020 Year 3 EOY Chemistry 6092 P2

1 ST JOSEPH’S INSTITUTION END-OF-YEAR EXAMINATION 2020 (YEAR 3) CANDIDATE NAME CLASS INDEX NUMBER CHEMISTRY Paper 2 Additional Materials: NIL 6092 / 02 1 OCTOBER 2020 1 hour 40 minutes (0800 - 0940) READ THESE INSTRUCTIONS FIRST Write your name, class and index number on all the work you hand in. Write in dark blue or black ink pen. You may use a 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 all questions in the spaces provided. At the end of the examination, fasten all your work securely together. The number of marks is given in brackets [ ] at the end of each question or part question. The use of an approved scientific calculator is expected, where appropriate. A copy of the Periodic Table is printed on page 2. For Examiner’s Use Section A / 40 Section B / 30 Total / 70 This document consists of 21 printed pages including this cover page.

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3 Section A Answer ALL questions in the spaces provided. The total mark for this section is 40. A1 An ester is a substance formed between the reaction of two organic compounds, an alcohol and an organic acid. An example of an ester is propyl ethanoate formed by the reaction of propanol (alcohol, C3H7OH, boiling point 97 °C) and ethanoic acid (organic acid, CH3COOH, boiling point 120 °C) with a small amount of concentrated sulfuric acid as a catalyst. (a) The glassware, as shown in Figure 1.1 and Figure 1.2 below, can be used for the formation of an ester, both using the same quantities of chemicals from the start. Figure 1.1 Figure 1.2 (i) Suggest a reason for using a water bath instead of direct heating. …………………....….……………………………………………………………. ………..…………………………………………………..…………………….[1] HEAT water bath test tube Liebig condenser Mixture of propanol, ethanoic acid and concentrated acid water bath HEAT

4 (ii) After heating the reaction mixture for a while, a student discovered that the percentage yield of ester from the set up in Figure 1.2 is less than that from the set up in Figure 1.1. Explain why. ………….….……………………………...………………………………………. ………….….…………………………………...…………………………………. ………….….………………………………...……………………………………. ………..……………………………………..………………………………….[2] (b) Esters can be used as solvents in chromatography. The following shows a chromatogram of plant acids which is drawn to scale. An ester was used as the solvent and the chromatogram was sprayed with a locating agent, bromothymol blue. sample 1 sample 2

5 (i) Suggest why it was necessary to spray the chromatogram with bromothymol blue. ..................................................................................................................... …………………………………................................................................. [1] (ii) Using evidence from the chromatogram, state which sample is more soluble in the ester. ..................................................................................................................... ………………………………….................................................................. [1] (iii) Explain what is meant by the Rf value of a sample. ..................................................................................................................... …………………………………….............................................................. [1]

6 (iv) Calculate the Rf values of the two samples and use the data in the table to identify the plant acids. sample 1 Rf = ................................................................. It is .............................. acid. sample 2 Rf = ............................................ It is .............................. acid. [2] [Total : 8]

7 A2 Pure stearic acid melts at 69.3⁰C and boils at 361⁰C. A solid sample of stearic acid was heated to 80⁰C and allowed to cool to 30⁰C. The graph of temperature versus time for the cooling process is shown below. (a) Describe the changes in movement and arrangement of the stearic acid particles as temperature decreases from 80⁰C to 68⁰C. ………......................................................................................................................... ………......................................................................................................................... ………......................................................................................................................... ……………….……………………………..……….....................................................[2] (b) Draw, on the same axes in the graph above, the expected graph of temperature versus time if the sample of stearic acid was impure. [1] Temperature / ⁰C Time / s 80 69.3 30

8 (c) A pure sample of stearic acid was heated from 350⁰C to 370⁰C. State and explain, in terms of kinetic particle theory, the change in state that occurred. ………......................................................................................................................... ………......................................................................................................................... ………......................................................................................................................... ……………….………………………….................................................................... [2] [Total: 5] A3 The table shows some information about atoms of the elements P, Q, R and S. (The letters do not represent the atomic symbols of the elements.) Element Number of protons Number of neutrons Nucleon number Electronic configuration P 16 16 32 2,8,6 Q 12 12 24 2,8,2 R 18 22 S 17 18 35 2,8,7 (a) Complete the table above by filling in the nucleon number and electronic configuration for element R. [1] (b) Explain why element R tends to be monatomic. ……………………………………………………………………………………….…...….. ……..…...................................................................................................................[1]

9 (c) Describe the change in electronic configuration of an atom of element Q when it combines with an atom of element P. ………......................................................................................................................... ……………….………………………….................................................................... [1] (d) Elements P and S combine to form a compound. Draw a ‘dot-and-cross’ diagram to show the bonding in this compound. Your diagram should show only valence electrons. [2] (e) Another isotope of element S has a nucleon number of 37. Isotopes of elements have different physical properties but similar chemical properties. (i) Define the term ‘isotope’. ………............................................................................................................... ……………….…………………………............................................................[1]

10 (ii) Explain why the isotopes of elements possess similar chemical properties. ………............................................................................................................... ……………….…………………………............................................................[1] [Total: 7] A4