SAJC Prelim P3_Qns

1   [Turn over NAME Class ST ANDREW’S JUNIOR COLLEGE JC2 PRELIMINARY EXAMINATION Chemistry (9729) Paper 3 Free Response 15 September 2017 2 hours Additional Materials: Data Booklet, Writing Paper READ THESE INSTRUCTIONS: 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. Section A Answer all questions. Marks [60] Section B Answer one question. Marks [20] The use of an approved scientific calculator is expected, where appropriate. A Data Booklet is provided. 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. This document consists of 14 printed pages (including this page).

2   [Turn over Section A Answer all the questions in this section. 1 (a) Iodine is a lustrous purple-black solid at standard conditions that sublimes readily to form a violet gas. (i) Give the equation that represents the second ionisation energy of iodine. [1] (ii) The graph below shows the second ioni sation energies of eight elements with consecutive atomic number. Which of the above elements, A to H, is iodine? Explain your answer.   [2] (iii) Explain the trend in second ioni sation energies from elements A to G, including the irregularity for element B. [4] (iv) Suggest, with reason, which of the above elements, A to H, can form an amphoteric oxide. Hence, write an equation to show the reaction of this amphoteric oxide with hydrochloric acid. (You are not requi red to provide the identity of the element in the equation.) [2] A B C D E F G H Second Ionisation energy/ kJ mol-1 Proton number

3   [Turn over 1 (b) Hydrogen peroxide reacts with acidified iodide ions to liberate iodine, according to the following equation: H2O2(aq) + 2H+(aq) + 2I(aq)  2H2O(l) + I2(aq) The rate of reaction can be measured by the increase in the concentration of iodine formed over time. The reaction was determined to be zero order with respect to [H+]. The following results were obtained by va rying the concentrations of hydrogen peroxide and iodide ions. Expt Initial [H 2O2(aq)] / mol dm-3 Initial [I(aq)] / mol dm-3 Initial rate / mol dm3 min1 1 0.020 0.040 1.2 x 10 -4 2 0.020 0.050 1.5 x 10 -4 3 0.050 0.040 3.0 x 10 -4 4 0.020 0.500 1.5 x 10 -3 5 0.050 1.000 7.5 x 10 -3 (i) What is understood by the terms order of reaction and half-life. [2] (ii) Determine the order of the reaction with respect to [H 2O2] and [ I] and hence suggest the units of the rate constant of this reaction. [3] (iii) The half-life of hydrogen peroxide in experiment 4 was 9. 24 min. Predict the half-life of hydrogen peroxide in experiment 5. [1] To investigate the rate of the abov