2021 JPJC Prelim P4 Answer Scheme

¤ Jurong Pioneer Junior College [Turn Over NAME CLASS 20S JURONG PIONEER JUNIOR COLLEGE JC2 PRELIMINARY EXAMINATION 2021 CHEMISTRY (Ans Scheme) 9729/04 Higher 2 Paper 4 Practical 17 August 2021 2 hours 30 minutes Candidates answer on the Question paper. Additional Materials: As listed in the Confidential Instructions READ THESE INSTRUCTIONS FIRST Write your name, class and exam index number on all the work you hand in. Give details of the practical shift and laboratory where appropriate, in the boxes provided. Write in dark blue or black pen. You may use a HB pencil for any diagrams, graphs. Do not use staples, paper clips, glue or correction fluid. Answer all questions in the spaces provided on the Question Paper. The use of an approved scientific calculator is expected, where appropriate. You may lose marks if you do not show your working or if you do not use appropriate units. Qualitative Analysis Notes are printed on pages 17 and 18. Shift At the end of the examination, fasten all your work securely together. Laboratory The number of marks is given in brackets [ ] at the end of each question or part question. For Examiner’s Use 1 2 3 Total This document consists of 17 printed pages and 1 blank page.

2 ¤ Jurong Pioneer Junior College 9729/04/J2 PRELIMINARY EXAM/2019 Answer all the questions in the spaces provided. 1 Determination of the solubility product of calcium iodate Calcium iodate, Ca(IO3)2, is a sparingly soluble salt and can dissociate in water according to the following equation. equation 1 Ca(IO3)2(s) Ca2+(aq) + 2IO3(aq) In this experiment you will determine the solubility product of calcium iodate, Ca(IO3)2. A saturated solution of calcium iodate was prepared, the concentration of iodate ions, IO3, in this saturated solution can be determined by reacting IO3 ions with an excess of I ions to form iodine, I2. equation 2 IO3– + 5I– + 6H+ → 3I2 + 3H2O The amount of iodine formed may be titrated against a standard solution of Na2S2O3 as shown in equation 3. equation 3 I2 + 2S2O32– → 2I – + S4O62– FA 1 is a filtered saturated solution of calcium iodate, Ca(IO3)2. FA 2 is an aqueous strong acid FA 3 is 0.500 mol dm3 potassium iodide, KI. FA 4 is 0.150 mol dm3 sodium thiosulfate, Na2S2O3. (a) (i) Titration of FA 1 against FA 4 1. Fill the burette with FA 4. 2. Use a pipette to transfer 25.0 cm3 of FA 1 into a 250 cm3 conical flask. 3. Use a measuring cylinder to add 25 cm3 of FA 2 to the conical flask. 4. Use another measuring cylinder to add 10 cm3 of FA 3 to the conical flask. The solution will turn brown as iodine is produced. 5. Run FA 4 from the burette into this flask. Near the end-point, when the yellow solution becomes pale, add about 1 cm3 of starch in