2021_RI_H2_Chem_Prelims_P4_Questions

1 © Raffles Institution 2021 9729/04/A/21 [Turn Over CANDIDATE NAME ( ) CLASS 21S0 RAFFLES INSTITUTION 2021 YEAR 6 PRELIMINARY EXAMINATION Higher 2 CHEMISTRY Paper 4 Practical 9729/04 25 August 2021 2 hours 30 minutes Do NOT turn over the Question Booklet until you are told to do so. READ THESE INSTRUCTIONS FIRST. Write your name and class on the space provided when instructed to do so. Give details of the practical shift and laboratory where appropriate, in the space provided. Write in dark blue or black pen. You may use a HB pencil for any diagrams or graphs. Do not use staples, paper clips, glue or correction fluid. Answer all questions in the spaces provided on the Question Paper. The number of marks is given in brackets [ ] at the end of each question or part question. 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 23 and 24. Shift Laboratory Bench Number For Examiner’s Use Question Marks 1 / 16 2 / 11 3 / 14 4 / 14 Total / 55 This Question Paper consists of 23 printed pages and 1 blank page.

2 © Raffles Institution 2021 9729/04/A/21 1 Determination of the solubility product of calcium iodate(V) Calcium iodate(V), Ca(IO3)2, has low solub ility in water. When a sample of this salt is mixed with water, a small amount dissolves and the following equilibrium is established in a saturated solution of Ca(IO3)2. Ca(IO3)2(s) ⇌ Ca2+(aq) + 2IO3–(aq) You are to perform an experiment to determine the solubility product, Ksp, of Ca(IO3)2(s). When a sample of solid Ca(IO3)2 is added to a mixture containing specific volumes of aqueous potassium iodate(V), KIO3(aq), and aqueous potassium nitrate, KNO3(aq), both of known concentrations, a small amount of solid dissolves and the above equilibrium is established after some time. The mixture is then filtered and the amount of iodate(V) ions, IO3, in the filtrate is determined as described below.  Excess potassium iodide is added to an acidified solution of the filtrate containing IO3 ions and iodine is liberated, as shown in equation 1. equation 1 IO3–(aq) + 5I–(aq) + 6H+(aq)  3I2(aq) + 3H2O(l)  The liberated iodine is then titrated wit