SRJC H2 Chem 2013 Prelim P2 QP

1   SRJC 9647/02/Prelim/2013 Turn Over]   SERANGOON JUNIOR COLLEGE General Certificate of Education Advanced Level Higher 2 CANDIDATE NAME CLASS CHEMISTRY 22 Aug 2013 9647/02 2 hours Preliminary Examination Paper 2 Structured Questions (SPA) Additional Materials: 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 work. Answer all questions in the space provided. You are advised to spend 30 minutes on question 1. At the end of the examination, fasten all your work securely together. The number of marks is given in the brackets [ ] at the end of each question or part questions.                       This document consists of 16 printed pages For Examiner’s Use 1(P) /12 2 /12 3 /17 4 /12 5 /7 6 /12 TOTAL P2 /72 For Examiner’s Use P1 /40 P2 /72 P3 /80 GRAND TOTAL /192 % GRADE 1251

2   SRJC 9647/02/Prelim/2013 Turn Over]   Answer all questions in the space provided Planning 1 Hard water, or water that contains high mineral content, such as calcium ions, pose serious problems in many industries. Other potential ions that could be present include zinc (through corrosion of pipings) and aluminium ions (whereby aluminium salts are added during the water purification process to start certain precipitation reactions). You are provided with a water sample that may contain the cations Ca 2+, Al3+ and Zn2+. The solution may also contain carbonate ions, CO 3 2–, and halide ions (either bromide or iodide). You are given only the following to conduct your test. Reagent Apparatus  aqueous ammonia  tests tubes  aqueous sodium hydroxide  funnel  dilute sulfuric acid  filter paper (a) Using the above only, write out a plan to separate each cation into three separate solutions. In your plan you should:  give a full description of the procedures you would use;  indicate the expected observations in each step. .................................................................................................................................... .................................................................................................................................. .................................................................................................................................... .................................................................................................................................. .................................................................................................................................... .................................................................................................................................. .................................................................................................................................... .................................................................................................................................. .................................................................................................................................... .................................................................................................................................. .................................................................................................................................... .................................................................................................................................. .................................................................................................................................... .................................................................................................................................. [5] For Examiners’ Use 1252

3   SRJC 9647/02/Prelim/2013 Turn Over]   (b) A student proposed to use concentrated sulfuric acid instead of dilute sulfuric acid in (a). (i) Discuss how this change may affect the expected observations in (a). ........................................................................................................................ ........................................................................................................................ (ii) Identify one potential safety hazard when the student make this change and state how you would minimise this risk. ........................................................................................................................ ........................................................................................................................ [4] (c) You are also required to identify the anions present in the solution. (i) Propose two reagents to identify and distinguish between CO 3 2– and halide ion. ........................................................................................................................ (ii) Outline how you would use your chosen reagents, including conditions, to determine the anions present in the solution. In your plan you should:  give a full description of the of the order of adding the reagent;  quantity of reagent and apparatus used;  indicate the expected observations. ........................................................................................................................ ........................................................................................................................ ........................................................................................................................ ........................................................................................................................ ........................................................................................................................ ........................................................................................................................ [3] [Total: 12] For Examiners’ Use 1253

4   SRJC 9647/02/Prelim/2013 Turn Over]   2 Iodometry is a technique used to analyse the concentration of an oxidising agent. To a sample of hydrogen peroxide, excess but known amount of iodide is used which the oxidising agent oxidises the iodide to triiodide ion. The triiodide ion solution is then titrated against standard thiosulfate solution using starch indicator. The reactions are illustrated below. Reaction 1 : H 2O2 + 3I- + 2H+  I3 - + 2H2O Reaction 2 : I3 - + 2S2O3 2-  3I - + S4O6 2- (a) Iodine exists as a black solid at standard conditions. An aqueous solution of iodine can only be prepared by dissolving iodine in excess potassium iodide, KI (aq) to form a dark reddish-brown solution. (i) Suggest a reason for the insolubility of iodine in water. ......................................................................................................................... ................................