2017 RVHS H2 Chemistry P3 Soln

River Valley High School 9729/03/PRELIM II/17 [Turn over 2017 Preliminary Examination II RIVER VALLEY HIGH SCHOOL YEAR 6 PRELIMINARY EXAMINATION II CANDIDATE NAME CLASS 6 CENTRE NUMBER S INDEX NUMBER H2 CHEMISTRY 9729/03 Paper 3 Free Response 19 September 2017 2 hours Candidates answer on separate paper. Additional Materials: Answer Paper Cover Page Data Booklet READ THESE INSTRUCTIONS FIRST Write your name, class, centre number and index number on all the work you hand in. Write in dark blue or black pen on both sides of paper. 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 questions. Section B Answer one question. Begin each question on a fresh sheet of paper. The use of an approved scientific calculator is expected, where appropriate. A Data Booklet is provided. Do not write anything on it. 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, with the cover page on top. This document consists of XX printed pages.

2 River Valley High School 9729/03/PRELIM II/17 2017 Preliminary Examination II Section A Answer all the questions in this section. 1 (a) Under suitable conditions, SCl2 reacts with water to produce a yellow solid and an acidic solution A. Solution A contains a mixture of SO 2(aq) and another compound. (i) State the oxidation number of S in SCl2 . [1] +2 (ii) Construct an equation for the reaction between SCl2 and water. [1] 2SCl2 + 2H2O → S + SO2 + 4HCl (iii) In the Contact Process, one important step is the conversion of SO2 to SO3 as shown below. 2SO2(g) + O2(g) ⇌ 2SO3(g) A 2.00 L flask was filled with 0.0400 mol SO 2 and 0.0200 mol O 2. At equilibrium, the flask contained 0.0296 mol of SO3. Determine the value of Kc, stating its unit. [3] 2SO2 + O2 ⇌ 2SO3 I / mol 0.04 0.02 0 C / mol −0.0296 0.0148 +0.0296 E / mol 0.0104 0.0052 0.0296 Kc = [0.0296 2⁄ ]2 [0.0104 2⁄ ]2[0.0052 2⁄ ] = 3116 = 3120 mol–1 dm3

3 River Valley High School 9729/03/PRELIM II/17 [Turn over 2017 Preliminary Examination II (b) During the electrolysis of dilute sulfuric acid using a current of 0.75 A for 90 min and platinum electrodes, the volume of oxygen gas collected wa s recorded and is shown in the Table 1.1 below. Table 1.1 Time / min Volume of O2 gas / cm3 20 55 40 110 60 165 80 220 (i) Plot a graph of volume of O2 gas over time. Use x axis: 2 cm for 10 min ; y axis: 2 cm for 50 cm3 [2] See graph paper (ii) Give equations for the reactions that occur at each electrode in the electrolysis of sulfuric acid. [2] Cathode: 2H2O(l)