2016 HCI H1 Chemistry Prelims P2 Questions

HCI H1 Chemistry Prelim 2016 HWA CHONG INSTITUTION Preliminary Examination Higher 1 CANDIDATE NAME CT GROUP 15S CHEMISTRY Paper 2 Candidates answer Section A on the Question Paper. Additional Materials: Data Booklet Writing paper; Graph paper 8872/02 30 August 2016 2 h READ THESE INSTRUCTIONS FIRST Write your name and CT group on all the work you hand in. Write in dark blue or black pen. You may use a pencil for any diagrams, graphs or rough working. Do not use staples, paper clips, highlighters, glue, correction fluid or tapes. Section A Answer all 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 EXAMINERS’ USE ONLY Paper 1 Paper 2 TOTAL Multiple Choice Section A (Structured) Section B (Free Response) Q1 /10 Q4 / 20 Q2 /14 Q5 / 20 Q3 /16 Q6 / 20 / 30 Subtotal / 40 Subtotal / 40 This question booklet consists of 13 printed pages. 110

H1 Chemistry Prelim 2016 2 Section A Answer all the questions in this section in the spaces provided. 1 (a) An equilibrium exists between aqueous chromate (VI) ions and dichromate (VI) ions as shown by the expression below: 2CrO 42-(aq) + 2H+(aq)  Cr2O72-(aq) + H2O(l) Yellow orange (i) State the meaning of the term dynamic equilibrium. ………………………………………………………………………………………. ………………………………………………………………………………………. ……………………………………………………………………………………[1] (ii) Write an expression for the equilibrium constant, K c, for this reaction. [1] (iii) The initial concentration of CrO 42- ions and H+ ions are 0.850 mol dm−3 and 1.20 mol dm−3 respectively. After equilibrium is reached, the concentration of Cr2O72- ions is 0.200 mol dm−3. Calculate the value of K c for this equilibrium and state its units. Kc = ……………………. units = ……………………. [3]

H1 Chemistry Prelim 2016 3 (b) (i) State Le Chatelier’s Principle. ………………………………………………………………………………………. ……………………………………………………………………………………… …………………………………………………………………………………….. …………………………………………………………………………………[1] (ii) Describe and explain what happens to the colour in the beaker when aqueous sodium hydroxide is added. ………………………………………………………………………………………. ………………………………………………………………………………………. ………………………………………………………………………………………. ………………………………………………………………………………………. ……………………………………………………………………………………[2] (iii) When the beaker containing aqueous chromate (VI) and dichromate (VI) ions in equilibrium is heated, the solution becomes more yellow. Explain whether the equilibrium is exothermic or endothermic. ………………………………………………………………………………………. ………………………………………………………………………………………. ………………………………………………………………………………………. ………………………………………………………………………………………. …………………………………………………………………………………… [2] [Total: 10]

H1 Chemistry Prelim 2016 4 2 (a) A, B, C, D, E and F are all structural isomers with the molecular formula C4H8O A, B and C all give an orange precipitate when treated with 2,4- DNPH but only A and B give a brick-red precipitate when warmed with Fehling’s solution. (i) Draw the structural formulae of A, B and C A B C (ii) Name the type of structural isomerism shown by A and B …………………………………………………………………………………………….. (iii) State what you would see when a sample of A is warmed with Tollens’ reagent. …………………………………………………………………………………………….. …………………………………………………………………………………………….. …………………………………………………………………………………………….. (iv) State the reagents used that give a positive test for C but not A and B. ……………………………………………………………………………………………… [6]

H1 Chemistry Prelim 2016 5 (b) (c) D, E and F (all with molecular formulae C 4H8O) all decolourise bromine and effervescence slowly with sodium metal. E shows geometrical isomerism. Only D has branched chain. None of these isomers contains C=O (i) Give the structures of D, E and F. Show the two stereoisomers of E and label the stereoisomerism shown. D E …………… E ……………….. F (ii) Write balanced equation showing how one of these isomers react with sodium metal. ………………………………………………………………………………………………. [6] Another compound, G, C3H6O, has the same functional group as A. Give equations for the reactions of G with acidified potassium dichromate(VI) and sodium tetrahydridoborate, NaBH4, using [O] or [H] as appropriate. (i) reaction with acidified potassium dichromate(VI) ……………………………………………………………………………………………….. (ii) reaction with sodium tetrahydridoborate NaBH 4 ……………………………………………………………………………………………….. [2] [Total: 14]

H1 Chemistry Prelim 2016 6 3 ‘Water gas’ is an equimolar mixture of hydrogen and carbon monoxide. It is used as a gaseous fuel in the industry. It is produced when steam is blown through white-hot coke in the following reaction. H 2O(g) + C(s)  H2(g) + CO(g) Another widely-used industrial fuel is natural gas, which consists mainly of methane. Hoc values are given in the table below. Substance Standard enthalpy change of combustion, Hoc/ kJ mol–1 CH4 -890 H2 -242 CO -283 C -394 (a) (i) Define the term standard enthalpy change of combustion,Hoc …………………………………………………………………………………….. …………………………………………………………………………………….. ……………………………………………………………………………………… ……………………………………………………………………………………. .[2] (ii) Using the data given, calculate the volume of methane required to produce 1 MJ of heat energy when burned. [2] (iii) Calculate the volume of “water gas” required to produce the same amount of heat energy as methane. (1 mole of gas occupies 22400 cm 3 at stp) [2]

H1 Chemistry Prelim 2016 7 (b) In recent years, there has been worldwide interest in the extraction of ‘shale gas’ as an important energy source. One of the problems associated with using shale gas is its variable composition. Table 1 shows the percentage composition of shale gas from four different sources J, K, L and M. Percentage composition Source of shale gas CH4 C2Hx C3Hy CO 2 N 2 J 80.3 8.1 2.3 1.4 7.9 K 82.1 14.0 3.5 0.1 0.3 L 88.0 0.8 0.7 10.4 0.1 M 77.5 4.0 0.9 3.3 14.3 Table 1 In the formulae above, x and y and variables. (i) Draw the structures of three possible compounds with the formula C 3Hy. [2] (ii) Which source of shale gas J, K, L or M, will provide the most energy when burned? Explain your answer. ………………………………………………………………………………….. ………………………………………………………………………………… …………………………………………………………………………………. ………………………………………………………………………………. ……[1] (iii) Suggest two methods (physical or chemical) by which carbon dioxide can be removed from shale gas. 1. ………………………………………………………………………….. …………………………………………………………………………………….