ACJC H1 CHEM P2 Qn paper

Index No. Name Form Class Tutorial Class Subject Tutor ANGLO-CHINESE JUNIOR COLLEGE DEPARTMENT OF CHEMISTRY Preliminary Examination CHEMISTRY 8873/02 Higher 1 Paper 2 16 August 2018 2 hours Candidates answer on the Question Paper Additional Materials: 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. Section A Answer all the questions. Section B Answer one question. The use of an approved scientific calculator is expected, where appropriate. 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 B7 B8 Presentation of answers TOTAL This document consists of 22 printed pages and 2 blank pages. 8873/02/Prelim/18 ANGLO-CHINESE JUNIOR COLLEGE © ACJC 2018 Department of Chemistry [Turn over

2 © ACJC 2018 8873/02/Prelim/2018 [Turn over BLANK PAGE

3 © ACJC 2018 8873/02/Prelim/2018 [Turn over Section A Answer all the questions in this section, in the spaces provided. 1 (a) Hydrogen sulfide, H 2S, is a foul-smelling compound found in the gases from volcanoes. Hydrogen sulfide has a melting point at –85°C and boiling point at –60°C. (i) State the structure of hydrogen sulfide. ……………………………………………………………………………………[1] (ii) Draw a ‘dot-and-cross’ diagram to show the structure of H 2S. [1] (iii) State and explain the shape of H 2S. ……………………………………………………………………………………… ……………………………………………………………………………………[2] (iv) Oxygen and sulfur are both in Group 16 of the Periodic Table. Suggest why the melting and boiling points of water, H 2O, are much higher than those of H2S. ……………………………………………………………………………………… ……………………………………………………………………………………… ……………………………………………………………………………………… ……………………………………………………………………………………… ……………………………………………………………………………………[3]

4 © ACJC 2018 8873/02/Prelim/2018 [Turn over (b) Hydrogen sulfide burns with a blue flame in an excess of oxygen to form sulfur dioxide and water. (i) Write a balanced equation for the complete combustion of H2S. ……………………………………………………………………………………[1] (ii) What is the change in the oxidation number of sulfur in this reaction? ……………………………………………………………………………………[1] (iii) What volume of oxygen, measured at room temperature and pressure, is required for the complete combustion of 8.65 g of H2S? Give your answer to two decimal places. [2] (c) Hydrogen sulfide is a weak diprotic (dibasic) acid. (i) What is meant by the term weak acid? ……………………………………………………………………………………[1] (ii) Write an equation, with state symbols, for the first ionisation of H 2S when it dissolves in water. ……………………………………………………………………………………[1] [Total: 13]

5 © ACJC 2018 8873/02/Prelim/2018 [Turn over 2 (a) In 2010 the Nobel Prize for Physics was awarded to two researchers from Manchester University for their work on preparing graphene from graphite. (i) Graphene can be prepared from graphite by using sticky tape. Use your knowledge of the bonding in graphite to explain why it is possible to create graphene by this method. ……………………………………………………………………………………[1] (ii) State one physical property of graphene and explain the reason. ……………………………………………………………………………………… ……………………………………………………………………………………[2] (b) A graphene sheet is a layer of graphite. A recent development has been the synthesis of graphene ribbons (reported in Nature, 2010). A reaction scheme is shown. (i) When monomer A is polymerised to make B there is also another product, X. Give the molecular formula of X. [1] (ii) In the transformation of polymer B into polymer C, another product, Y, is produced. Give the molecular formula of Y. [1]

6 © ACJC 2018 8873/02/Prelim/2018 [Turn over (iii) Deduce the number of moles of X and Y produced per mole of monomer A. [2] (iv) Boron nitride, BN, forms sheets similar to graphene except they contain dative covalent bonds as well as covalent bonds. Add all the possible dative covalent bonds between the atoms shown in the structure below. [1] (v) Boron nitride can also form a giant covalent structure in which each atom has four single bonds. Suggest the name of another substance which has this type of structure. ……………………………………………………………………………………[1] [Total: 9]

7 © ACJC 2018 8873/02/Prelim/2018 [Turn over 3 Chemists have recently found a way of making the strong, light-weight and thermally stable polymer, Kevlar®, to be antibacterial (reported in Industrial & Engineering Chemistry Research, 2008). This was achieved by coating it with another polymer, a fragment of which is shown below. O HN Cl O HN Cl O HN Cl polymer (a) Draw the repeat unit of the polymer structure shown above. [1] (b) The polymer shown above is made by the following reactions: reaction 1 an addition polymerisation reaction of a monomer known as MAA reaction 2 the substitution of a hydrogen atom in the polymer with a chlorine atom using bleach Draw the structure of the monomer MAA. [1]

8 © ACJC 2018 8873/02/Prelim/2018 [Turn over (c) Not all the nitrogen atoms in the polymer end up bonded to a chlorine atom. The quantity of chlorine actually present in the polymer can be determined using reactions 3, 4 and 5. A known mass of polymer (written as XCONH–Cl) is reacted to convert the chlorine content of the polymer to chloric(I) acid, HOCl: reaction 3 XCONH–Cl + H2O XCONH 2 + HOCl (where X = remainder of polymer) The chlorine content is then ‘converted’ to iodine: reaction 4 HOCl + 2K I + H+ I2 + KCl + H2O + K+ The quantity of iodine is determined using a titration with sodium thiosulfate: reaction 5 I2 + 2Na2S2O3 2Na I + Na2S4O6 (i)