RVHS Prelim P4 QP

River Valley High School Pg 1 of 24 JC 2 H2 Chemistry 9729 2020 Prelim Practical Examination RIVER VALLEY HIGH SCHOOL JC 2 PRELIM PRACTICAL EXAMINATION H2 CHEMISTRY 9729 Paper 4 25 AUGUST 2020 2 HOURS 30 MINUTES NAME CLASS INDEX NO. INSTRUCTIONS TO CANDIDATES DO NOT OPEN THIS BOOKLET UNTIL YOU ARE TOLD TO DO SO. Read these notes carefully. Write your name, class and index number in the spaces at the top of this page. 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 2B pencil for any diagrams or graph. Do not use staples, paper clips, highlighters, 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. Shift Laboratory For Examiner’s Use s.f. / d.p. units total 55 _________________________________________________________________________________ This Question Paper consists of 23 printed pages and 1 blank page.

River Valley High School Pg 2 of 24 JC 2 H2 Chemistry 9729 2020 Prelim Practical Examination Answer all the questions in the space provided. 1 Determination of a value for the solubility product, Ksp, of calcium iodate(V), Ca(IO3)2 For Examiner’s Use Calcium iodate (V), Ca(IO3)2, is a colourless salt that occurs naturally as the mineral, lautarite. It is used in the manufacture of disinfectants, antiseptics, deodorants and as iodine supplement in chicken feed. Ca(IO3)2 has low solubility in water. When a sample of this salt is mixed with water, the following equilibrium is established. 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). Ca(IO3)2(s) is added to a specific volume of aqueous potassium iodate(V), KIO3, with known concentration. The mixture is then filtered after leaving to stand for some time. The total amount of IO3(aq) is determined as described below. Excess potassium iodide, K I, is added to an acidified solution of the filtrate, liberating iodine. Reaction 1 IO3(aq) + 5I(aq) + 6H+(aq)  3I2(aq) + 3H2O(l) The liberated iodine is then titrated with a standard solution of sodium thiosulfate. Reaction 2 2S2O32(aq) + I2(aq)  2I(aq) + S4O62(aq) (a) Write an expression for the solubility product, Ksp, of calcium iodate(V). 1 (b) The following procedure is used to prepare a saturated solution of calcium iodate(V) in aqueous potassium iodate(V), FA 1. You do not need to perform this part of the experiment. 1. Using a measuring cylinder, transfer 100.0 cm3 of 0.0100 mol dm3 KIO3 to a clean, dry beaker. 2. Add 2 spatulas of solid Ca(IO3)2 to the same beaker. 3. Stir the mixture thoroughly. There should be undissolved solid Ca(IO3)2 present. Leave the mixture to stand for several minutes to allow equilibrium to be reached. 4. Filter the mixture through a dry filter paper into a dry conical flask to collect the filtrate, FA 1 for titration in (c).

River Valley High School Pg 3 of 24 JC 2 H2 Chemistry 9729 2020 Prelim Practical Examination (c) You are provided with FA 1 filtrate from (b), a saturated solution of Ca(IO3)2 in KIO3(aq) FA 2 0.100 mol dm3 sodium thiosulfate, Na2S2O3 FA 3 aqueous solution of potassium iodide, KI FA 4 dilute sulfuric acid, H2SO4 Starch indicator Titration of filtrate, FA 1 1. Pipette 25.0 cm3 of FA 1 into a conical flask. 2. Using a measuring cylinder, add about 10 cm3 of FA 4 to the conical flask. 3. Using a nother measuring cylinder, add about 10 cm3 of FA 3 to the conical flask. 4. Add FA 2 from the burette into the conical flask until a pale yellow solution is obtained. 5. Add about 5 drops of starch indicator and continue adding FA 2 until the blue-black colour just disappears. 6. Record your titration results, to an appropriate level of precision, in the space below. 7. Repeat the titration as many times as necessary until consistent results are obtained. For Examiner’s Use Supervisor’s mean Student’s mean Difference 2 3 4 5 6 Results

River Valley High School Pg 4 of 24 JC 2 H2 Chemistry 9729 2020 Prelim Practical Examination (c) (i) From your titrations, obtain a suitable volume of FA 2 (VFA 2) to be used in your calculations. Show clearly how you obtained this volume. For Examiner’s Use VFA 2 = …………………………… 7 (ii) Use the volume of FA 2 obtained in (c)(i) to calculate the amount of IO3(aq) present in 25.0 cm3 of FA 1. amount of IO3(aq) present in 25.0 cm3 of FA 1 = …………..…………… 8 (iii) Calculate the amount of IO3(aq) in the mixture from (b) at equilibrium. amount of IO3(aq) in the mixture = ……..………………… 9

River Valley High School Pg 5 of 24 JC 2 H2 Chemistry 9729 2020 Prelim Practical Examination (d) (i) Calculate the amount of IO3 ions from the dissolved Ca(IO3)2 in (b). For Examiner’s Use amount of IO3(aq) from the dissolved Ca(IO3)2 = .................................. 10 (ii) Calculate the amount of Ca2+(aq) in the mixture from (b) at equilibrium. amount of Ca2+(aq) in the mixture = .............................. 11

River Valley High School Pg 6 of 24 JC 2 H2 Chemistry 9729 2020 Prelim Practical Examination (e) Use your answer in parts (c)(iii) and (d)(ii) to calculate a value for the solubility product, Ksp, of Ca(IO3)2 and give its units in your answer. For Examiner’s Use Ksp = .................................................................. 12 13 (f) In part (b) step 4, dry apparatus and dry filter paper are used in the preparation of FA 1. Suggest and explain the likely consequences on your mean titre value in part (c)(i) if the apparatus and filter paper were not dry. 14 (g) Another student prepared a solution of FA 1 and performed the titration. He obtained a value for the solubility product, Ksp, of 7.96  107. A literature value for this solubility product is 6.47  106 at 25 °C. You should assume that apparatus of the same precision were used in both cases. State a possible reason for the lower value of Ksp obtained by the student. 15 [Total: 15]

River Valley High School Pg 7 of 24 JC 2 H2 Chemistry 9729 2020 Prelim Practical Examination 2 To investigate the effect of concentration changes on the rate of reaction between iodate(V) ion and sulfate(IV) ion. For Examiner’s Use Iodate(V), IO3, undergoes redox reaction with sulfate(IV), SO32, according to the equation below: 2IO3 + 5SO32 + 2H+  I2 + 5SO42 + H2O However, t he iodine formed reacts immediately with sulfate (IV) ions to give iodide ions. I2 + SO32 + H2O  2I + SO42 + 2H+ When sulfate( IV) ions are completely consumed, the liberated iodine would react with starch solution to give the dark blue colour of the starch -iodine complex. By measuring the time it takes for the solution to turn dark blue, it is possible to determine the effect of the concentrations of H+ and IO3 on the initial rate of the reaction between IO3 and SO32. FA 5 is 0.0160 mol dm3 aqueous potassium iodate(V), KIO3. FA 6 is 0.100 mol dm3 sulfuric acid, H2SO4. FA 7 is 0.0400 mol dm3 aqueous sodium sulfate(IV), Na2SO3. You are to perform a series of three experiments, in which the concentration of either H+, or IO3 is varied, and measure the time, t, taken for the dark blue colour to appear. For each experiment, you will require two solutions, solution A and solution B, in which