2024 DHS Y6 H1 Prelim Paper 2_Suggested Solutions

© DHS 2024 8873/02 [Turn over Suggested Solutions DUNMAN HIGH SCHOOL Preliminary Examination Year 6 H1 CHEMISTRY Paper 2 Structured Questions Candidates answer on the Question Paper. Additional Materials: Data Booklet 8873/02 11 September 2024 2 hours READ THESE INSTRUCTIONS FIRST Write your centre number, index number, name and class at the top of this page. Write in dark blue or black pen. You may use an HB pencil for any diagrams or graphs. Do not use staples, paper clips, glue or correction fluid. Answer all questions in the spaces provided on the Question Paper. Section A Answer all questions. Section B Answer one question. The use of an approved scientific calculator is expected, where appropriate. You may lose marks if you do not show your working or if you do not use appropriate units. 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 Section A 1 10 2 13 3 17 4 20 Section B 5 / 6 20 Total 80 This document consists of 20 printed pages.

2 © DHS 2024 8873/02 Section A Answer all the questions in the spaces provided. 1 (a) Petrol is a mixture of hydrocarbons that includes octane, C8H18. The density of petrol is typically 748.9 kg per litre and comprises 95% octane by mass. (i) Write an equation for the complete combustion of octane. [1] C8H18(l) + 25 2 O2(g) → 8CO2(g) + 9H2O(l) (ii) Calculate the volume of carbon dioxide gas that will be emitted at r.t.p., if a full tank carrying 50 litres of petrol is completely combusted. You should assume that only octane undergoes combustion. [3] Mass of octane combusted = 50 × 0.95 × 748.9 = 35572.75 kg No. of mol of octane combusted = 35572.75 ×1000 114 = 3.12 × 105 mol Since C8H18  8CO2, no of mol of CO2 emitted = 3.12 × 105 × 8 = 2.50 × 106 mol Volume of CO2 emitted at r.t.p. = 2.50 × 106 × 24 = 5.99 × 107 dm3 (iii) Ethanol is sometimes added to the petrol for internal combustion engine. The standard enthalpy change of combustion of ethanol, Hc, can be determined by applying Hess’ Law to the energy cycle in Fig. 1.1. Fig. 1.1 Express the standard enthalpy change of combustion of ethanol, Hc, in terms of x, y and z. [1] Hc = –x + y + z (iv) State the type of enthalpy change that x represents. [1] standard enthalpy change of formation of ethanol (b) Exhaust gases from internal combustion engine are harmful to the environment. These include oxides from carbon and nitrogen. (i) Write an equation to show the removal of carbon monoxide and nitrogen monoxide from the exhaust gases. [1] 2NO(g) + 2CO(g) → 2CO2(g) + N2(g) 7 2ൗ