HCI H2 Chem 2013 Prelim P3 QP

This document consists of 11 printed pages and 1 blank page. HWA CHONG INSTITUTION C2 Preliminary Examinations Higher 2 CANDIDATE NAME CT GROUP 12S CENTRE NUMBER INDEX NUMBER CHEMISTRY Paper 3 Free Response Candidates answer on separate paper. Additional Materials: Answer Paper Data Booklet 9647/03 20 September 2013 2 hours INSTRUCTIONS TO CANDIDATES Write your name and class on all the work you hand in. Write in dark blue or black pen. 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 new piece of paper. 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 question. At the end of the examination, fasten all your work securely together. Write down the question numbers for the questions that you have attempted on the cover page provided. 646

2 © Hwa Chong Institution 2013 9647 / 03 / C2 Prelim 2013 Answer any four questions. 1 (a) Sodium chloride and sodium iodide react differently when warmed with concentrated sulfuric acid. Describe what you would observe when these reactio ns are carried out, write equations for the reactions that occur and suggest an explanation for these different reactions. Include state symbols in your equations. [5] Solvent extraction is an analytical technique which involves extracting a solute dissolved in one solvent with another solvent. The two solvents must be immiscible with each other. The ratio of the concentrations of the solute in the two solvents at equilibrium is a constant value called the partition coefficient. For this partition law to hold true, the solute must exist in the same molecular form in both solvents. (b) At room tem perature, an aqueous solution of iodine containing 1.20 × 10 −3 mol dm −3 of iodine was found to be in equilibrium with a solution in tetrachloromethane containing 0.102 mol dm−3 of iodine. Calculate the partition coefficient of iodine betwe en tetrachlor omethane and water, and comment on the significance of the value obtained. [2] (c) When iodine is dissolved in aqueous potassium iodide, it forms the triiodide complex ion according to the following equilibrium. I2(aq) + I−(aq) ⇌ I3 −(aq) reaction 1 To determine the equilibrium constant of the above reaction, a solution of iodine dissolved in 0.100 mol dm −3 aqueous potassium iodide was shaken with tetrachloromethane until equili