2021_TJC_H2Chemistry Prelim_P4

1 [Turn over DO NOT WRITE IN THIS MARGIN DO NOT WRITE IN THIS MARGIN DO NOT WRITE IN THIS MARGIN 9729 / TJC Prelim / 2021 CANDIDATE NAME CIVICS GROUP / CENTRE NO. / INDEX NO. / CHEMISTRY 9729/04 Paper 4 Practical 26 August 2021 2 hours 30 minutes Candidates answer on the Question Paper. READ THESE INSTRUCTIONS FIRST Write your Civics Group and name 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 an 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 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 19 and 20. At the end of the examination, fasten all your work securely together. The number of marks is given in brackets [ ] at the end of each question or part question. This document consists of 20 printed pages. For Examiner’s Use 1 / 12 2 / 17 3 / 14 4 / 12 Total / 55 Shift Laboratory 2021 JC2 PRELIMINARY EXAMINATIONS HIGHER 2

2 [Turn over DO NOT WRITE IN THIS MARGIN DO NOT WRITE IN THIS MARGIN DO NOT WRITE IN THIS MARGIN 9729 / TJC Prelim / 2021 Answer all the questions in the spaces provided. 1 Determination of water of crystallisation in a hydrated iron(III) salt A variety of hydrated iron(III) sulfates are known. Solutions of iron(III) sulfate are used in dyeing as a mordant, and as a coagulant for industrial wastes. FA 1 is hydrated iron(III) sulfate with formula Fe2(SO4)3.nH2O. The addition of excess zinc to a solution of FA 1 reduces the Fe3+ ions to Fe2+ ions. The amount of Fe2+ ions can be determined quantitatively by titration against a standard solution of potassium manganate(VII), KMnO4. The reaction is shown below. 5Fe2+ + MnO4- + 8H+ ® 5Fe3+ + Mn2+ + 4H2O In this experiment, you are to prepare a standard solution using FA 1 and perform titrations to determine the value of n, the water of crystallisation in FA 1. You are provided with FA 2, dilute sulfuric acid, FA 3, 0.0200 mol dm-3 potassium manganate(VII), KMnO4, zinc powder. (a) Preparation of standard solution of hydrated iron(III) salt 1. Weigh accurately about 6.5 g of the FA 1 provided using the weighing bottle. Transfer all the solid into a 250 cm3 beaker. Determine the mass of solid FA 1 used and record all your weighings, to an appropriate level of precision, in the space below. [1] 2. Use a measuring cylinder to add about 100 cm3 of FA 2 to the beaker. Stir the mixture with a glass rod for 3 minutes. Ignore any c