ACJC H1 CHEM P2 Qns

Index No. Name Form Class Tutorial Class Subject Tutor ANGLO-CHINESE JUNIOR COLLEGE DEPARTMENT OF CHEMISTRY Preliminary Examination CHEMISTRY 8872/02 Higher 1 Paper 2 16 August 2016 2 hours Candidates answer Section A on the Question Paper Additional Materials: Writing Paper Data Booklet READ THESE INSTRUCTIONS FIRST Write your name, index number, form class, tutorial class and subject tutor’s 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 staples, paper clips, glue or correction fluid. The use of an approved scientific calculator is expected, where appropriate. Section A Answer all the questions. Section B Answer two questions on separate answer paper. 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. For Examiner's Use Question no. Marks Section A B4 B5 B6 TOTAL This document consists of 16 printed pages. 8872/02/Prelim/16 ANGLO-CHINESE JUNIOR COLLEGE © ACJC 2016 Department of Chemistry [Turn over

2 © ACJC 2016 8872/02/Prelim/2016 [Turn over Section A Answer all questions in this section in the spaces provided. 1 The element chromium was discovered in 1797 by French chemist Louis Nicolas Vauquelin. A number of naturally occurring isotopes of chromium have been identified as listed below. isotope relative isotopic mass natural abundance (%) 50Cr 49.95 4.34 52Cr 51.94 83.79 53Cr 52.94 9.50 54Cr 53.94 2.37 (a) Use the above data to calculate the relative atomic mass of chromium to two decimal places. [2] Chromium is a transition metal. (b) (i) Describe the bonding in the element chromium. Draw a diagram to illustrate your answer. ………………………………………………………………………………………….. ……………………………………………………………………………………… [1]

3 © ACJC 2016 8872/02/Prelim/2016 [Turn over (ii) State two physical properties that you would expect chromium metal to possess. Explain, in terms of the bonding present, why it possesses these properties. property ………………………………………………….……… explanation .…………………… …………………………………………………..... …………………………………………………………………………….................. …………………………………………………………………………………...…..... property ………………………………………………….……… explanation .…………………… …………………………………………………..... …………………………………………………………………………….................. …………………………………………………………………………………...…...[3] (iii) Chromium metal is produced by reducing chromium( III) oxide with aluminium or silicon. State the full electronic configuration of a chromium atom, Cr and a chromium ion, Cr 3+. Cr …………………………………………………………….………………………… Cr3+ …………………………………………………..……….………………………… [2] (c) A student put 5 cm 3 of dilute sulfuric acid in a boiling tube. He added 5 drops of potassium dichromate( VI) solution and then 2 drops of ethanol. He heated the mixture until it just boiled. (i) What colour change would the student see as he carried out this reaction? from …………………... to ………………………….. [1] (ii) Name the organic product formed and the type of reaction that has occurred. product ………………………………………………………………………………. type of reaction ……………….……………………………………........................ [2]

4 © ACJC 2016 8872/02/Prelim/2016 [Turn over (d) The students then carried out another reaction of ethanol using the apparatus shown in the diagram below. The broken porcelain used contains Al2O3. (i) What is the name of the gas collected in the gas jar? …………………………………………………………..………………………… [1] (ii) What type of reaction has the ethanol undergone? ………………………………………………………………………………………[1] (e) What reagent and conditions are necessary to convert propanone into propan-2-ol? …………………………………………………………………………………………......[1] [Total: 14] 2 Tin forms an oxide, A, that contains the metal in both oxidation states II and IV. The formula of A can be found by the following method. • A sample of A was dissolved in H2SO4(aq), producing solution B, which was a mixture of tin(II) sulfate and tin(IV) sulfate. First titration • A 25.0 cm3 sample of solution B was titrated with 0.0200 mol dm –3 KMnO4. 13.50 cm3 of KMnO4 was required to reach the end-point. Second titration • Another 25.0 cm3 sample of solution B was stirred with an excess of powdered zinc. This converted all the tin( IV) into tin( II). The excess of zinc powder was filtered off and the filtrate was also titrated with 0.0200 mol dm -3 KMnO4, as before. This time 20.30 cm 3 of KMnO4 was required to reach the end-point. The equation for the reaction occurring during the titration is as follows. 2MnO 4– + 16H+ + 5Sn2+ 2Mn2+ + 8H2O + 5Sn4+

5 © ACJC 2016 8872/02/Prelim/2016 [Turn over (a) (i) Write a balanced ionic equation with state symbols for the reaction between Zn and Sn4+. ………………………………………………………………………………………[1] (ii) Use the results of the two titrations to calculate • the number of moles of Sn2+ in the first titration sample, • the number of moles of Sn2+ in the second titration sample. [3] (iii) Use the results of your calculation in (ii) to deduce the Sn 2+/ Sn4+ ratio in the oxide A, and hence suggest the formula of A. [2]

6 © ACJC 2016 8872/02/Prelim/2016 [Turn over (b) A major use of tin is to make ‘tin plate’, which is composed of thin sheets of mild steel electroplated with tin, for use in the manufacture of food and drinks cans. A tin coating of 1.0 x 10–5 m thickness is often used. (i) Calculate the volume of tin needed to coat a sheet of steel 1.0 m x 1.0 m to this thickness, on one side only. [1] (ii) Calculate the number of moles of tin that this volume represents. [The density of tin is 7.3 g cm –3.] [2] [Total: 9] 3 (a) (i) Define the term standard enthalpy change of formation. …………………………………………………………………………………………… …………………………………………………………………………………………… ……………………………………………………………………………………….[1]

7 © ACJC 2016 8872/02/Prelim/2016 [Turn over (ii) Carbon, hydrogen and ethene each burn exothermically in an excess of air. C(s) + O2(g) CO 2(g) ∆Hc = –393.7 kJ mol–1 H2(g) + ½O2(g) H 2O(l) ∆Hc = –285.9 kJ mol–1 C2H4(g) + 3O2(g) 2CO 2(g) + 2H2O(l) ∆Hc = –1411.0 kJ mol–1 Write an equation for