2020 RI Prelim P4 Question paper

© Raffles Institution 2020 9729/04/A/20 [Turn Over CANDIDATE NAME ( ) CLASS 20S0 RAFFLES INSTITUTION 2020 YEAR 6 PRELIMINARY EXAMINATION Higher 2 CHEMISTRY Paper 4 Practical 9729/04 26 August 2020 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 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 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 19 and 20. Shift Laboratory Bench Number For Examiner’s Use Question Marks 1 / 17 2 / 15 3 / 12 4 / 11 Total / 55 This document consists of 18 printed pages and 2 blank pages.

2 © Raffles Institution 2020 9729/04/A/20 [Turn Over Answer all the questions in the spaces provided. 1 Determination of the concentration of hydrogen peroxide and the relative formula mass of hydrated halotrichite Halotrichite is a mineral which is formed by the weathering and decomposition of pyrite commonly found near volcanic vent s. Halotrichite contains Fe2+, one other cation and one anion. Both potassium manganate(VII) and hydrogen peroxide are oxidising agents which will oxidise the Fe2+ in halotrichite to Fe3+ under acidic conditions. equation 1 MnO4−(aq) + 5Fe2+(aq) + 8H+(aq) ⎯→ Mn2+(aq) + 5Fe3+(aq) + 4H2O(l) equation 2 2Fe2+(aq) + H2O2(aq) + 2H+(aq) ⎯→ 2Fe3+(aq) + 2H2O(l) You may assume that the other cation and the anion present in halotrichite do not react with potassium manganate(VII) and hydrogen peroxide. FA 1 is a solution formed by dissolving 22.26 g of hydrated halotrichite in 100 cm3 of water. FA 2 is 0.0200 mol dm−3 potassium manganate(VII), KMnO4. FA 3 is aqueous hydrogen peroxide, H2O2. FA 4 is 0.800 mol dm–3 sulfuric acid, H2SO4. Note: FA 1 and FA 4 are also used in questions 3 and 2 respectively. In Exp