CJC H2 Chem 2012 Prelim P3 QP

CATHOLIC JUNIOR COLLEGE JC2 PRELIMINARY EXAMINATIONS Higher 2 CHEMISTRY 9647/03 Paper 3 Free Response Friday 24 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. [PILOT FRIXION ERASABLE PENS ARE NOT ALLOWED] 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. 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 of the question. At the end of the examination, fasten all your work securely together. This document consists of 14 printed pages and 0 blank page. [Turn over

2 9647/03/CJC JC2 Preliminary Exam 2012 Answer any four questions. 1 This question relates to the chemistry of Be, Mg, Al and their compounds. (a) Beryllium compounds are toxic air pollutants. Inhalation of high levels of beryllium can cause inflammation of the lungs in humans and long-term exposure may cause chronic beryllium disease (berylliosis), in which granulomatous lesions develop in the lung. (i) Given that charge density ∝ ionic charge ionic radius , calculate the relative charge densities of Be2+, Mg2+ and Al3+, using relevant data from the Data Booklet. (ii) Hence, predict what is observed when aqueous sodium hydroxide is gradually added to aqueous beryllium sulfate until the sodium hydroxide is in an excess . Write equations for all reactions that have taken place. (iii) Suggest the pH of the solution formed when beryllium chloride is dissolved in water. Give your reasoning. (iv) Magnesium ions are essential for the action of some enzymes (e.g. alkaline phosphatase found in the liver) by receiving electron pairs from oxygen and nitrogen atoms in the protein. It is thought that beryllium compounds are poisonous because they displace magnesium ions from these enzymes. Suggest a reason why beryllium ions should behave in this way. (v) Beryllium chloride may be used as a catalyst in the chlorination of benzene. Suggest a reason why this is possible. O utline the mechanism to show how beryllium chloride is involved in this reaction. [10]

3 9647/03/CJC JC2 Preliminary Exam 2012 [Turn over (b) A student carried out a kinetics experiment using a roll of magnesium ribbon that had been exposed to air for some time. He placed a piece of magnesium ribbon of mass 0.12 g into a flask containing 15.0 cm 3 of 1.0 mol dm–3 hydrochloric acid. The progress of the reaction was followed by measuring the pressure of the system at different times. The graph below shows the results of the experiment. (i) Determine, by calculation, the limiting r