ACJC Chemistry Paper 3 Questions Prelims

Centre Number Index Number Name and Class ANGLO-CHINESE JUNIOR COLLEGE PRELIMINARY EXAMINATIONS Advanced Level CHEMISTRY 9746/03 Higher 2 Paper 3 Free response 18 August 2008 2 hours Candidates answer on separate paper. Additional Materials: Data Booklet READ THESE INSTRUCTIONS FIRST Write your name, Centre number and index number on all the work you hand in. Write in dark blue or black pen. You may use a soft pencil for any diagram, graphs or rough working. Do not use staples, paper clips, highlighters, glue or correction fluid. Answer any four questions. A Data Booklet is provided. 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. At the end of the examination, fasten all your work securely together including the cover page. Write down the question numbers that you have attempted in the table below. For Examiner's Use Question no. Marks TOTAL This question paper consists of 8 printed pages including the cover page.

Paper 3 (80 marks) Answer any four questions 1 (a) When aqueous bromine reacts with methanoic acid, carbon dioxide gas is produced. Br 2 (aq) + HCOOH (aq) 2 Br - (aq) + 2 H+ (aq) + CO2 (g) The rate of the reaction can be determined by measuring the rate of formation of carbon dioxide gas. In investigations of this reaction, the following results were obtained. Initial concentrations / mol dm -3 Experiment [Br2] [HCOOH] Initial rate of formation of CO2 (g) / mol dm-3 s-1 1 0.01 0.02 2.0 x 10-6 2 0.02 0.04 8.0 x 10-6 3 0.03 0.02 6.0 x 10-6 (i) Deduce the order of the reaction with respect to Br2 and HCOOH. Hence, write a rate equation for the reaction. [3] (ii) Using the data from Experiment 3 , calculate the rate constant for the reaction, stating its units. [2] (iii) What conclusions about the mechanism of the reaction can you draw from the rate equation? [2] (iv) In another experiment, equal volumes of 0.01 mol dm -3 of Br 2 and 0.02 mol dm -3 of HCOOH were mixed. What is the initial rate of this experiment? [2] (b) The relative molecular mass and the boiling point of methanal, methanol and methanoic acid are given in the table below. Compounds Relative Molecular Mass Boiling Point / °C Methanal 30.0 -21.0 Methanol 32.0 64.7 Methanoic Acid 46.0 100.7 (i) Explain the differences in their boiling points. [3] (ii) In benzene solution, the measured relative molecular mass of methanoic acid is approximately 92.0. Explain the observation and include relevant diagram in your answer. [2] (c) Suggest a simple chemical test to distinguish the following pairs of compounds. You should include the reagent, conditions, observations and relevant balanced equations for each test. [6] (i) Methanal and methanoic acid (ii) Methanoic acid and ethanoic acid [Total: 20] © ACJC 2008 9746/03/Prelim/08 2

2 (a) A cell consisting of a Cu2+ (aq) Cu (s) half-cell and a Fe3+ (aq), Fe2+ (aq) Pt (s) half cell is shown below, using conventional notation. Cu (s) Cu2+ (aq) Fe3+ (aq), Fe2+ (aq) Pt (s) (i) What do you understand by the term standard electrode potential? [2] (ii) Calculate the standard cell potential, Eθ, of this cell [1] (iii) Write the equation for the reaction occurring in each half cell, and hence write a balanced equation for the overall reaction which takes place when current flows. [2] (iv) If a current is drawn from the cell, what will happen to the concentration of the ions in the solution of Fe 3+ (aq), Fe2+ (aq) Pt (s) half cell? [1] (v) What is the change in mass of the copper electrode if a current of 1 ampere is drawn from the cell for 30 seconds? [2] (vi) State with reason what you expect to happen if the Cu 2+ (aq) Cu (s) half cell connected to Fe 3+ (aq), Fe 2+ (aq) Pt (s) half cell is replaced by Co3+ (aq), Co2+ (aq) Pt (s) half cell. [2] (b) An Fe/Fe 2O3 catalyst is used in the synthesis of ammonia in the Haber Process N2 (g) + 2 H2 (g) 2 NH 3 (g) ΔHo negative But no catalyst was used in the synthesis of nitrogen monoxide N 2 (g) + O2 (g) 2 NO (g) ΔHo positive Explain the observation of the usage of catalyst in one synthesis and not in the other. [4] (c) One substance which is responsible for the fragrance of roses is 2-phenylethanol, C 6H5CH2CH2OH. It can be synthesized from methylbenzene by the following series of reactions Cl2 II III IV C6H5CH3 → C6H5CH2Cl → C6H5CH2CN → P → C6H5CH2CH2OH (i) Suggest reagents and conditions for steps II and III. [2] (ii) Describe the mechanism of the reaction that will take place when methylbenzene is subjected to excess chlorine in the presence of iron filing. [2] (iii) Suggest an identity for compound P. [1] (iv) What types of reaction are steps III and IV? [2] [Total: 20] © ACJC 2008 9746/03/Prelim/08 3

3 Hydrogen halides result from the chemical reaction of hydrogen with one of the halogen elements (fluorine, chlorine, bromine, iodine). They are hydrohalic acids because of their ability to release hydronium (H 3O+) ions in aqueous solution. (a) HCl, HBr and HI form acidic white fumes in moist air under room temperature and pressure conditions. The addition of concentrated sulfuric acid to these three hydrogen halides separately can be used as a distinguishing test. You should state what you would observe for each compound when concentrated sulfuric acid is added. Write balanced equations with state symbols for any reactions that occur. [3] (b) Describe what is happening in the following phenomena. Write balanced equations with state symbols for the reactions that occur in each of the following phenomena. (i) Chlorine gas turns moist starch-iodide paper blue. [2] (ii) Reaction of chlorine with aqueous potassium hydroxide at different temperatures will produce different products. [2] (c) (i) X and Y are Period III elements. Element X forms a white oxide that is slightly soluble in cold water. Its chloride dissolves in water to form a weakly acidic solution. Element Y forms two oxides. 0.03 mol of one of the two oxides produces 6.99 g of white precipitate when shak