RI Prelim P3_QP

© Raffles Institution 2015 9647/03/S/15 [Turn Over RAFFLES INSTITUTION 2015 YEAR 6 PRELIMINARY EXAMINATION Higher 2 CHEMISTRY 9647/03 Paper 3 Free Response September 2015 Candidates answer on separate paper. 2 hours Additional Materials: Writing Paper Data Booklet Cover Page READ THESE INSTRUCTIONS FIRST DO NOT open this question booklet until you are told to do so. Write your name, class and index number in the spaces provided on the cover page. 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 each question on a fresh sheet of paper. 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 examina tion, fasten all your work securely together, with the cover page on top. ______________________________________________________________________________ This document consists of 13 printed pages.

2 © Raffles Institution 2015 9647/03/S/15 Answer any four questions. Begin each question on a fresh sheet of paper. 1 Calcium is the fifth most abundant element found in the Earth’s crust. It is commonly found in the form of salts and oxides as limestone, marble and chalk. (a) Finely powdered calcium metal can cause spontaneous explosions in air. Explain briefly why this is so, writing chemical equations where appropriate. [2] (b) Calcium metal is produced mainly by the electrolysis of molten calcium chloride at 800 °C. (i) Determine the mass (in tonnes ) of calcium metal that can be obtained when 1 x 10 5 A of current is passed through an electrolytic cell for 3 hours. [1 tonne = 1000 kg] [2] (ii) With the use of the Data Booklet, explain why the electrolysis of calcium chloride cannot be conducted in aqueous medium. [1] (c) When 2.0 g of calcium ethanoate, Ca(CH3CO2)2, was heated to 450 °C, only propanone and a white solid, M, were produced. (i) Write a balanced equation for the thermal decomposition of calcium ethanoate and state the identity of the white solid M. [1] (ii) On further heating, partial decomposition of solid M occurs to give off carbon dioxide and a white residue. The white residue contains 70% by mass of solid M. Calculate the mass of carbon dioxide evolved from the partial decomposition.