SAJC_H1_CHEM_P2_student_solutions

Name: Class: ST ANDREW’S JUNIOR COLLEGE JC2 Preliminary Examination ANSWERS Chemistry Higher 1 8872/2 Paper 2 17th September 2015 1400 - 1600 2 hours Additional Materials: Writing paper, Data Booklet, OAS READ THESE INSTRUCTIONS FIRST Write your name and civics group 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, highlighters, glue or correction fluid. Section A: Answer all the questions in this section in the spaces provided. Section B: Answer two questions from this section on separate answer paper. You are reminded of the need for good English and clear presentation in your answers. The number of marks is given in brackets [ ] at the end of each question or part question. For Examiners use only: This document consists of 19 printed pages including this page. [Turn Over

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Section A Answer all the questions in this section in the spaces provided. 1 Jet airliners use kerosene as fuel. The formula of kerosene can be taken as C14H30. It can be converted into more useful small molecules by the process of cracking. (a) (i) To which homologous series does kerosene belong? [1] Alkane (ii) Write a balanced equation to show the cracking of kerosene into heptane, propene and ethene only. [1] C14H30 → C7H16 + C3H6 + 2 C2H4 (iii) Suggest a use of ethene during the cracking process. [1] Any one of the following:  form poly(ethene) used as plastic  form bromoethane to add to the petrol to remove lead  form ethanol which used as a solvent  form ethane-1,2-diol to act as anti freeze. (iv) With the aid of an equation, define standard enthalpy change of combustion of kerosene. [1] C14H30(l) + 43/2 O2 (g) → 14 CO2 (g) + 15 H2O (l) (b) Fill in the boxes with the appropriate structures and state the reagents and conditions of steps I and II.

[5] (c) The propene obtained from cracking of kerosene is bubbled into acidified potassium manganate(VII) solution to form ethanoic acid. 20 cm 3 of the ethanoic acid produced is titrated with 3.0 mol dm -3 aqueous NaOH using a suitable indicator. The average volume of NaOH used is 12.50 cm3. Another 20 cm 3 of the same ethanoic acid is placed into a plastic cup of negligible heat capacity. A 10.0 cm3 sample of 3.0 mol dm-3 aqueous NaOH, at the same initial temperature, is added into the plastic cup. The temperature of the mixture rises by 12.5 K. (i) Determine the concentration of the ethanoic acid. [1] CH3COOH + NaOH CH3COO−Na+ + H2O CaVa =CbVb Ca(20) =3.0(12.50)

Ca = 1.875 mol dm-3 (ii) If the specific heat capacity per unit volume of the mixture is 4.2 J K -1 cm-3, what is the enthalpy change of neutralization of ethanoic acid? [2] Heat release = mc∆T = 3