JJC H2 Chem 2012 Prelim P3 QP

JURONG JUNIOR COLLEGE JC 2 PRELIMINARY EXAMINATION Higher 2 CANDIDATE NAME CLASS EXAM INDEX NUMBER CHEMISTRY 9647/03 Paper 3 Free Response 27 August 2012 2 hours Candidates answer on separate paper. Additional Materials: Answer Paper Data Booklet READ THESE INSTRUCTIONS FIRST Write your name and class on all the work you hand in. Write in dark blue or black pen on both sides of the 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. Answer any four questions. Begin your answer to each new question on a fresh sheet of writing paper. At the end of the examination, arrange the answers in numerical order and attach the cover sheet on top. A Data Booklet is provided. Do not write anything on the Data Booklet. 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. 1 2 3 4 5 This document consists of 10 printed pages and 0 blank pages. [Turn over

Answer any four questions. 1. Use of the Data Booklet is relevant to the question. (a) Hydrogen can play an important role in the future by replacing the petroleum currently used in automobiles. For example, electric cars can be powered by hydrogen-oxygen fuel cells, with its hydrogen fuel kept at extremely high pressures in thick-walled storage tanks. (i) State the half equations for the reactions occurring at each of the electrodes in a hydrogen-oxygen fuel cell operating under acidic conditions. (ii) Describe one disadvantage of using a hydrogen-oxygen fuel cell over internal combustion engines in automobiles. (iii) A quantity of hydrogen gas is confined in a chamber of constant volume. When the chamber is placed at a temperature of 20°C, the pressure of the gas is 3.29  105 Pa. What will be the pressure of the gas, in Pa, if the chamber is now placed in a water bath of boiling water to simulate the operating temperature of a certain automobile? [5] (b) A student designed an ion-specific probe to determine the concentration of H + ions in solution. He connected a hydrogen electrode to a calomel reference electrode, which comprises a paste of mercury( I) chloride and mercury in a saturated chloride electrolyte solution. The porous glass frit acts as a salt bridge. The hydrogen electrode, sensitive to H+ ion concentration, is the measuring electrode. Therefore, this galvanic cell acts as a pH meter. When both electrodes are in contact with the test solution, an electric current flows through the wire and mercury(I) chloride reacts to form liquid mercury and chloride ion at the reference electrode. Under standard conditions, the Ecell of the pH meter is +0.28 V. (i) Construct the half equation for the reaction occurring at the r