2022 DHS Y6 H2 Prelim Paper 4_Suggested Solutions

This document consists of 16 printed pages. © DHS 2022 9729/04 [Turn over Suggested Solutions DUNMAN HIGH SCHOOL Preliminary Examination Year 6 H2 CHEMISTRY Paper 4 Practical Candidates answer on the Question Paper. 9729/04 25 August 2022 2 hours 30 minutes READ THESE INSTRUCTIONS FIRST Write your centre number, index number, name and class 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 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 sci entific 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 21 and 22. 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. Shift Laboratory For Examiner’s Use 1 16 2 10 3 14 4 15 Total 55

2 © DHS 2022 9729/04 Answer all questions in the spaces provided. 1 Determination of solubility product, Ksp, of magnesium carbonate The solubility of solid magnesium carbonate, MgCO3, in water is low. In this experiment, you will determine the solubility product, Ksp, of magnesium carbonate using volumetric analysis. MgCO3(s) ⇌ Mg2+(aq) + CO32–(aq) A saturated solution of magnesium carbonate was prepared by collecting the filtrate after mixing aqueous solutions of magnesium sulfate and sodium carbonate. You will then determine the amount of carbonate ions left in the filtrate using hydrochloric acid. FA 1 is a saturated solution of magnesium carbonate, MgCO3. FA 2 is 0.003 mol dm–3 hydrochloric acid, HCl. methyl orange indicator Note: • Read the procedures given in part (a) and part (b)(i). • Part (a) has been done for you. You are not required to carry out part (a), but you will still need to read part (a) to know how FA 1 is prepared. (a) Preparation of FA 1 1. Use a measuring cylinder to transfer 20 cm 3 of 0.100 mol dm–3 magnesium sulfate to a clean and dry 250 cm3 beaker. 2. Use a measuring cylinder to transfer 50 cm3 of 0.0400 mol dm–3 sodium carbonate to the same beaker. A white precipitate forms. 3. Stir the mixture thoroughly. Leave this mixture to stand for 15 minutes to allow equilibrium to be reached. 4. Filter the reaction mixture into a dry 250 cm3 conical flask, using dry filter funnel and filter paper. The filtrate is labelled as FA 1. Do not wash the white precipitate with water. (b) (i) Titration of FA 1 against FA 2 1. Fill a burette with FA 2. 2. Pipette 10.0 cm3 of FA 1 into a 100 cm3 conical flask. 3. Add a few drops of methyl orange indicat